Bibliografia sobre Agachamento

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1: Eur Spine J. 2007 May;16(5):687-99. Epub 2006 Nov 14.

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Analysis of squat and stoop dynamic liftings: muscle forces and internal spinal loads.

Bazrgari B, Shirazi-Adl A, Arjmand N.

Department of Mechanical Engineering, Ecole Polytechnique, Montreal, QC, Canada.

Despite the well-recognized role of lifting in back injuries, the relative biomechanical merits of squat versus stoop lifting remain controversial. In vivo kinematics measurements and model studies are combined to estimate trunk muscle forces and internal spinal loads under dynamic squat and stoop lifts with and without load in hands. Measurements were performed on healthy subjects to collect segmental rotations during lifts needed as input data in subsequent model studies. The model accounted for nonlinear properties of the ligamentous spine, wrapping of thoracic extensor muscles to take curved paths in flexion and trunk dynamic characteristics (inertia and damping) while subject to measured kinematics and gravity/external loads. A dynamic kinematics-driven approach was employed accounting for the spinal synergy by simultaneous consideration of passive structures and muscle forces under given posture and loads. Results satisfied kinematics and dynamic equilibrium conditions at all levels and directions. Net moments, muscle forces at different levels, passive (muscle or ligamentous) forces and internal compression/shear forces were larger in stoop lifts than in squat ones. These were due to significantly larger thorax, lumbar and pelvis rotations in stoop lifts. For the relatively slow lifting tasks performed in this study with the lowering and lifting phases each lasting approximately 2 s, the effect of inertia and damping was not, in general, important. Moreover, posterior shift in the position of the external load in stoop lift reaching the same lever arm with respect to the S1 as that in squat lift did not influence the conclusion of this study on the merits of squat lifts over stoop ones. Results, for the tasks considered, advocate squat lifting over stoop lifting as the technique of choice in reducing net moments, muscle forces and internal spinal loads (i.e., moment, compression and shear force).

PMID: 17103232 [PubMed - indexed for MEDLINE]

PMCID: PMC2213554

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2: Phys Ther. 2000 Jun;80(6):570-7.

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Effects of squat lift training and free weight muscle training on maximum lifting load and isolinetic peak torque of young adults without impairments.

Yeung SS, Ng GY.

Department of Rehabilitation Sciences, The Hong Kong Polytechnic University, Hung Hom, Kowloon, Hong Kong.

BACKGROUND AND PURPOSE: Manual lifting is a frequent cause of back injury, and there is no evidence as to which training mode can provide the best training effect for lifting performance and muscle force. The purpose of this study was to examine the effects of a squat lift training and a free weight muscle training program on the maximum lifting load and isokinetic peak torque in subjects without known neuromuscular or musculoskeletal impairments. SUBJECTS: Thirty-six adults (20 male, 16 female) without known neuromuscular or musculoskeletal impairments participated. The subjects' mean age was 21.25 years (SD=1.16, range=20-24). METHODS: Subjects were divided into 3 groups. Subjects in group 1 (n=12) performed squat lift training. Subjects in group 2 (n=12) participated in free weight resistance training of their shoulder abductors, elbow flexors, knee extensors and trunk extensors. Subjects in group 3 (n=12) served as controls. The maximum lifting load and isokinetic peak torques of the trunk extensors, knee extensors, elbow flexors, and shoulder abductors of each subject were measured before and after the study. Training was conducted on alternate days for 4 weeks, with an initial load of 80% of each subject's maximum capacity and with the load increased by 5% weekly. RESULTS: All groups were comparable for all measured variables before the study. After 4 weeks, subjects in groups 1 and 2 demonstrated more improvement in maximum lifting load and isokinetic peak torque of the back extensors compared with the subjects in group 3, but the 2 training groups were not different. CONCLUSION AND DISCUSSION: The findings demonstrate that both squat lift and free weight resistance training are equally effective in improving the lifting load and isokinetic back extension performance of individuals without impairments.

Publication Types:

• Clinical Trial
• Randomized Controlled Trial

PMID: 10842410 [PubMed - indexed for MEDLINE]

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3: Spine. 2001 Aug 15;26(16):1794-8.

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The effect of wearing a back belt on spine kinematics during asymmetric lifting of large and small boxes.

Giorcelli RJ, Hughes RE, Wassell JT, Hsiao H.

Division of Safety Research, National Institute for Occupational Safety and Health, Morgantown, West Virginia 26505, USA.

STUDY DESIGN: A crossover design was used to evaluate kinematic measurements collected with an infrared-based motion measurement system. OBJECTIVES: To evaluate belt effects on spine kinematics during asymmetric lifting of large and small boxes and to test for carryover effects between trials from belts. SUMMARY OF BACKGROUND DATA: Conflicting evidence in the literature exists regarding whether belts are beneficial or detrimental to manual material handlers. Studies have not examined belt effects when lifting different sized boxes, nor carryover effects from belts. METHODS: Twenty-eight subjects with manual-handling experience (17 male and 11 female) were randomly assigned to lift either a large or small box (weighing 9.4 kg), from a sagittally symmetric origin at pallet height to a 79 cm height, 60 degrees to the right. Spine flexion, lateral bending and twisting, hip and knee flexion, and angular velocity measurements of the torso with respect to the pelvis were collected for each of three lifting periods, 50 lifts each at 3 lifts per minute, with 18-minute breaks between periods. RESULTS: Belts significantly reduced maximum spine flexion, spine flexion and extension angular velocities, and torso left lateral bending angular velocity, and increased hip and knee flexion, regardless of box size. When lifting large boxes, belts significantly reduced torso right lateral bending and torso left twisting. No significant differential carryover effects were detected from belts. CONCLUSIONS: Subjects with belts lifted more slowly and used more of a squat-lift technique, regardless of box size. Belts reduced more torso motions while lifting large boxes.

Publication Types:

• Clinical Trial
• Randomized Controlled Trial

PMID: 11493853 [PubMed - indexed for MEDLINE]

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4: Phys Ther. 1987 Sep;67(9):1329-34.

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Electromyographic analysis of two techniques for squat lifting.

Delitto RS, Rose SJ, Apts DW.

The purpose of this study was to examine the effects of two different alignments of the lumbar spine and three different loads on electromyographic activity of the erector spinae (ES) and oblique abdominal (OA) muscles during squat lifting. Nineteen healthy subjects (8 men, 11 women) participated in this study. Each subject performed squat lifts both with the lumbar spine aligned in "back-bowed-in" (BBI), or normal, lordosis and with the lumbar spine aligned in "back-bowed-out" (BBO), or relatively less, lordosis. Based on total duration, the lift was divided into two equal phases. Electromyographic activity of each muscle was quantified for each half of the lift and normalized to the total EMG produced by the muscle during a maximal voluntary isometric contraction. A three-way analysis of variance for repeated measures was used to analyze the effects of position of the lumbar spine, timing, and load on the amount of EMG activity during lifting. For all loads, ES muscle activity was greater during the first half of the BBI lift, whereas OA muscle activity was greater during the first half of the lift, regardless of the lifting style (p less than .01). The greater ES and OA muscle activity occurring during the crucial initial period in the BBI lift may provide the best protection for the lumbar spine.

Publication Types:

• Comparative Study
• Research Support, Non-U.S. Gov't

PMID: 2957703 [PubMed - indexed for MEDLINE]

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5: Ergonomics. 1998 Jun;41(6):790-7.

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Effect of semi-rigid lumbosacral orthosis use on oxygen consumption during repetitive stoop and squat lifting.

Duplessis DH, Greenway EH, Keene KL, Lee IE, Clayton RL, Metzler T, Underwood FB.

US Army-Baylor University Graduate Program in Physical Therapy, Medical Science Department, Fort Sam Houston, Texas 78234-6138, USA.

The use of back belts in industry has increased despite the lack of scientific evidence supporting their efficacy. The purpose of this study was to investigate the effect of a semi-rigid lumbosacral orthosis (SRLSO) on oxygen consumption during 6-min submaximal repetitive lifting bouts of 10 kg at a lifting frequency of 20 repetitions min-1. Fifteen healthy subjects (13 men, two women) participated in this study. Each subject performed squat and stoop lifting with and without an SRLSO for a total of four lifting bouts. Lifting bouts were performed in random order. Oxygen consumption during the final minute of each lifting bout was used for analysis. A two-way analysis of variance with repeated measures was used to analyse the effects of lift and belt conditions. The stoop and squat methods were significantly different, with the squat lift requiring 23% more oxygen on average than the stoop lift for equal bouts of work. No significant difference was found between the belt and no belt condition within the same lifting technique and no interaction was present. These data suggest that an SRLSO does not passively assist the paravertebral muscles (PVM) in stabilizing the spine during submaximal lifting bouts.

Publication Types:

• Clinical Trial
• Randomized Controlled Trial

PMID: 9629064 [PubMed - indexed for MEDLINE]

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6: Spine. 2007 Jul 1;32(15):1599-604.

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Regional changes in spine posture at lift onset with changes in lift distance and lift style.

Gill KP, Bennett SJ, Savelsbergh GJ, van Dieën JH.

Institute for Biophysical and Clinical Research into Human Movement, Department of Exercise and Sport Science, Manchester Metropolitan University, Alsager, UK. p.gill@salford.ac.uk

STUDY DESIGN: Repeated measures experiment. OBJECTIVE: To determine the effect of changes in horizontal lift distance on the amount of flexion, at lift onset, in different spine regions when using different lift styles. SUMMARY OF BACKGROUND DATA: By approximating spine bending during lifting as a pure rotation about a single revolute joint, the differential effects of task constraints and instructions on motions of different spine levels will be obscured. METHODS: Eight participants lifted a 10-kg crate from the floor, 10 times at each of five distances. Participants were instructed to use freestyle (a participant's preferred lift style), squat, or stoop lift styles. Kinematic data were collected from the mid thoracic spine, lower thoracic/upper lumbar spine, mid lumbar spine, and the lower lumbar spine at lift onset. A whole spine angle was also calculated. RESULTS: Flexion of the lower lumbar spine was not affected by lift distance and style. Differences between lift styles occurred mainly in the mid thoracic and the lower thoracic/upper lumbar regions. With increasing horizontal distance, changes in lift style occurred in the upper three spine regions. CONCLUSIONS: These results suggest that the tensile strain on tissues in the lower lumbar spine, which can be a cause of injury in lifting, was not affected by lift style or horizontal lift distance when lifting from floor level.

PMID: 17621206 [PubMed - indexed for MEDLINE]

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7: Spine. 2005 Oct 15;30(20):2265-73.

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Torso flexion loads and the fatigue failure of human lumbosacral motion segments.

Gallagher S, Marras WS, Litsky AS, Burr D.

National Institute for Occupational Safety and Health, Pittsburgh, PA 15236-0070, USA. sgallagher@cdc.gov

STUDY DESIGN: Spine loads associated with lifting a 9-kg weight were estimated at three torso flexion angles (0 degrees, 22.5 degrees, and 45 degrees), and lumbosacral motion segments were cyclically loaded using these loads until failure or to a maximum of 10,020 cycles. OBJECTIVES: To simulate the postures and loads experienced by the lumbar spine during repetitive lifting of moderate weights in different torso flexion postures, and to analyze the fatigue failure response of lumbosacral motion segments. SUMMARY OF BACKGROUND DATA: Previous fatigue failure studies of lumbar motion segments have not reproduced the combination of spinal postures, loads, and load rates anticipated in different torso flexion postures during lifting tasks characteristic of those in occupational settings. METHODS: Twelve fresh human lumbosacral spines were dissected into three motion segments each (L1-L2, L3-L4, and L5-S1). Motion segments within each spine were randomly assigned to a simulated torso flexion angle (0 degrees, 22.5 degrees, or 45 degrees) using a partially balanced incomplete block experimental design. Spinal load and load rate were determined for each torso flexion angle using previously collected data from an EMG-assisted biomechanical model. Motion segments were creep loaded for 15 minutes, then cyclically loaded at 0.33 Hz. Fatigue life was taken as the number of cycles to failure (10 mm displacement after creep loading). Specimens were inspected to determine failure mechanisms. RESULTS: The degree of torso flexion had a dramatic impact on cycles to failure. Motion segments experiencing the 0 degrees torso flexion condition averaged 8,253 cycles to failure (+/-2,895), while the 22.5 degrees torso flexion angle averaged 3,257 (+/-4,443) cycles to failure, and motion segments at the 45 degrees torso flexion angle lasted only 263 cycles (+/-646), on average. The difference was significant at P < 0.0001, and torso flexion accounted for 50% of the total variance in cycles to failure. CONCLUSIONS: Fatigue failure of spinal tissues can occur rapidly when the torso is fully flexed during occupational lifting tasks; however, many thousands of cycles can be tolerated in a neutral posture. Future lifting recommendations should be sensitive to rapid development of fatigue failure in torso flexion.

Publication Types:

• Research Support, U.S. Gov't, Non-P.H.S.

PMID: 16227888 [PubMed - indexed for MEDLINE]

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8: Eur J Appl Physiol. 2008 Feb;102(3):299-305. Epub 2007 Oct 13.

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Peak lifting velocities of men and women for the reduced inertia squat exercise using force control.

Paulus DC, Reiser RF 2nd, Troxell WO.

Department of Mechanical Engineering, University of Arkansas-Fort Smith, P.O. Box 3649, Fort Smith, AR 72913-3649, USA. dpaulus@uafortsmith.edu

The purpose of the research was to determine peak velocities for the reduced inertia squat exercise at various resistance levels based on an isometric strength assessment for both men and women. On a Smith machine modified for pneumatic resistance, 12 males and 12 females previously trained college-age participants performed a maximal isometric strength assessment with knee angles of 90 degrees , 110 degrees , 130 degrees , 150 degrees and 170 degrees (180 degrees = full extension) followed by dynamic maximal effort squats with resistance maintained at 40, 50, 60, 70, and 80% of their lowest maximum isometric strength. No interaction existed between the men and women during isometric strength tests with the men stronger in every joint position (P < 0.05). The lowest isometric strength occurred at 90 degrees without variation. There was an interaction between men and women for peak lifting velocity during the dynamic lifts (P = 0.021) with the men producing higher velocities at all levels of resistance (P < 0.05). The difference in peak velocity between the sexes was greatest at the lowest resistance level and that difference was less significant at the higher resistance levels. The relationship between resistance force and peak lifting velocity is applicable to increasing the efficiency of the squat by maximizing force output per repetition by varying the resistance as the lifter approaches peak velocity similar to isokinetics with preloading and active instead of reactive resistance.

Publication Types:

• Research Support, Non-U.S. Gov't
• Research Support, U.S. Gov't, Non-P.H.S.

PMID: 17934755 [PubMed - indexed for MEDLINE]

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9: Phys Ther. 1995 Feb;75(2):133-44.

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Neuromuscular coordination of squat lifting, II: Individual differences.

Scholz JP, McMillan AG.

Physical Therapy Department, University of Delaware, Newark 19716.

BACKGROUND AND PURPOSE. This article reports individual differences in the coordination (ie, the relative timing of joint movements and muscle activity) of squat lifting identified by extended analysis of data reported in the authors' companion article in this issue. SUBJECTS. Two post hoc groups of 6 subjects each were identified from the original sample of 15 subjects based on qualitative differences in knee-lumbar spine relative motion plots during load acceleration. METHODS. Subjects lifted a crate containing 15% to 75% of their maximum lifting capacity using a symmetrical squat-lift technique. Movement kinematic data were obtained with videography, and the electromyographic (EMG) activity of the vastus lateralis and erector spinae muscles was recorded with surface EMG. Measurements of coordination derived both kinematically and via EMG and the kinematic data were examined for group differences. RESULTS. Subjects in group 2 limited lumbar spine motion during load acceleration for all loads lifted, whereas those in group 1 limited lumbar spine motion more when lifting the heaviest loads. These differences were obvious both qualitatively, via knee-lumbar spine relative motion plots, and quantitatively, via measures of the relative timing of joint motions early in the lift. The effect of load on the coordination of these joints was the same for both post hoc groups after initial load acceleration. Significant differences in other kinematic measurements were also found between these groups. CONCLUSION AND DISCUSSION. Despite specific instructions about how to lift the load, individual subjects coordinated their joints differently during the initial, accelerative phase of squat lifting. Individual differences in coordination in response to load increases could be categorized into two patterns, although the data of 2 subjects were difficult to categorize and thus not included in these analyses. Whether the two dominant patterns have consequences for stress to the joints during lifting remains to be determined.

Publication Types:

• Research Support, Non-U.S. Gov't

PMID: 7846133 [PubMed - indexed for MEDLINE]

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10: J Orthop Sports Phys Ther. 2001 Jun;31(6):316-23.

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Effect of soft lumbar support belt on abdominal oblique muscle activity in nonimpaired adults during squat lifting.

Warren LP, Appling S, Oladehin A, Griffin J.

Department of Allied Health, Chattanooga State Technical Community College, Tenn, USA.

STUDY DESIGN: A counterbalanced repeated measures design. OBJECTIVE: To determine the effect of a soft lumbar support on abdominal oblique muscle electromyography (EMG) during lifting. BACKGROUND: Use of a soft lumbar back support is a common preventive measure to reduce the incidence of back injuries. Because the abdominal oblique muscles stabilize the spine during lifting, wearing this support may alter the activity level of these muscles. METHODS AND MEASURES: Twenty nonimpaired subjects (14 women and 6 men, mean age 28.9 +/- 8.1 years) were tested using surface electrodes to record the EMG of the right abdominal oblique muscles during lifting with and without the support. RESULTS: A paired t test revealed a significant decrease in activity of the abdominal oblique muscles during lifting with the support (29.7 +/- 3.13 mV) compared to without it (33.3 +/- 3.05 mV). Of the 20 subjects, the 14 women showed decreased EMG amplitude during the lift with the lumbar support compared to without the support, while 5 of the men showed increased EMG amplitude with the support and 1 man showed no change. CONCLUSION: This finding suggests that the soft lumbar support may play some role in the stabilization of the lumbar region during lifting.

Publication Types:

• Clinical Trial
• Randomized Controlled Trial

PMID: 11411626 [PubMed - indexed for MEDLINE]

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11: Spine. 1998 Oct 1;23(19):2104-9.

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The effect of back belt use on isometric lifting force and fatigue of the lumbar paraspinal muscles.

Majkowski GR, Jovag BW, Taylor BT, Taylor MS, Allison SC, Stetts DM, Clayton RL.

United States Army-Baylor Graduate Program in Physical Therapy, San Antonio, Texas.

STUDY DESIGN: A repeated measures multivariate design to assess the effect of back belts on isometric lifting force and lumbar paraspinal muscle fatigue. OBJECTIVE: To determine the efficacy of lumbar back belts in minimizing a loss in isometric force production and fatigue of lumbar paraspinal muscles. SUMMARY OF BACKGROUND DATA: Increased prevalence of back belts in industry and lack of scientific evidence supporting them suggested additional research was needed. There has been no conclusive research to substantiate manufacturer claims that use of belts reduces fatigue of lumbar paraspinals. METHODS: Twenty-four subjects, 13 men and 11 women, were tested twice: once with and once without a belt. All subjects performed a dynamic lifting task at a rate of 10 lifts per minute for 20 minutes. Surface electromyograms from the lumbar paraspinals and isometric force measurements were recorded during a static maximal isometric lift at 0, 10, and 20 minutes. Load during the dynamic task was determined as 20% of initial maximum isometric force. Electromyographic data were used to detect changes in median power spectral frequencies. Muscular fatigue was indicated by a reduction in median power spectral frequency values or a decrease in isometric force-generating capacity. RESULTS: Multivariate and univariate analyses suggest that there is no effect on lumbar paraspinal muscle fatigue or isometric lifting force production as a result of back belt use. CONCLUSIONS: These findings do not support the use of back belts for the purpose of minimizing either lumbar paraspinal muscle fatigue or a loss in isometric lifting force production.

Publication Types:

• Clinical Trial
• Comparative Study
• Controlled Clinical Trial
• Research Support, U.S. Gov't, Non-P.H.S.

PMID: 9794055 [PubMed - indexed for MEDLINE]

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12: Spine. 2002 Nov 15;27(22):2514-20.

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Spine loading as a function of gender.

Marras WS, Davis KG, Jorgensen M.

Biodynamics Laboratory, Institute for Ergonomics, Ohio State University, Columbus, Ohio 43210, USA. marras.1@osu.edu

STUDY DESIGN: In vivo laboratory studies were conducted to investigate the spine loads imposed on men and women during a series of lifting tasks that varied in the degree of lifting control required by the subject. OBJECTIVE: To identify and understand differences in spine loading and musculoskeletal control strategies between men and women performing lifts of varying task complexity. SUMMARY OF BACKGROUND DATA: Few studies have examined differences in spine loading as a function of individual factors such as subject gender. Furthermore, no biomechanical studies have attempted to quantify and understand how differences in anthropometry between genders might influence muscle recruitment and subsequent spine loads. Because the modern workplace seldom discriminates between genders in job assignments, it is important to understand how differences in spine loading and potential low back disorder risk might be associated with gender differences. METHODS: For this study, 140 subjects participated in two separate experiments requiring different degrees of musculoskeletal motion control during sagittal plane lifting. The two experiments consisted of 35 men and 35 women performing lifts in which motion was isolated to the torso and 35 men and 35 women completing whole-body free-dynamic whole body lifts. An electromyography-assisted model was used to evaluate spine loading under these conditions. RESULTS: Absolute spine compression generally was greater for the men. Under the highly controlled (isolated torso) conditions, most differences were attributed solely to differences in body mass. Under a whole-body free-dynamic condition, significant differences in muscle coactivations resulted in greater relative compression and anterior-posterior shear spine loading for the women. CONCLUSIONS: Differences in spine loadings as a function of gender under the more controlled lifting conditions were primarily a function of different body masses. However, loading pattern differences existed between the genders under whole-body free-dynamic conditions as a result of kinematic compensations and increases in muscle cocontraction, with women generally experiencing greater relative loads. When spine tolerance differences are considered, one would expect that females would be at greater risk of musculoskeletal overload during lifting tasks.

Publication Types:

• Clinical Trial
• Research Support, U.S. Gov't, Non-P.H.S.

PMID: 12435984 [PubMed - indexed for MEDLINE]

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13: Clin Biomech (Bristol, Avon). 1995 Apr;10(3):122-127.

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Influence of weight and frequency on thigh and lower-trunk motion during repetitive lifting employing stoop and squat techniques.

Hagen K, Sørhagen O, Harms-Ringdahl K.

Norwegian Forest Research Institute, Ås, Norway.

Changes in kinematics as a function of lifting weight and frequency was investigated in sagittal symmetric repetitive lifting. For every lift cycle (lowering and lifting) the motion range between the upright position (0 degrees ) and the maximum angular displacement of the thigh and lower-trunk body segments was recorded. Ten subjects performed five repetitive lifting bouts with different weight/frequency combinations, using both stoop and squat lifting techniques. In total, 6384 lifts were analysed. The lifting weight or frequency did not influence the motion ranges in stoop lifting. In squat lifting the weight lifted did not appear to have any influence on the motion ranges, while the thigh motion range was significantly smaller at lifting frequency of 20 lifts min(-1) than at a frequency of 10. A significant gradual decrease in the thigh motion range and corresponding increase in the lower-trunk motion range were seen for a majority of the subjects during squat lifting at frequency 20. These changes suggest that quadriceps muscle strength is the limiting factor in repetitive squat lifting. Also the variation in motion ranges was greater in squat lifting than in stoop lifting. RELEVANCE: Forestry work involves frequent lifting. However, compliance in using squat lifting technique, which is recommended for safe lifting, is sometimes poor. Fatigue may be one of the determinants for changes in kinematics and choice of technique in lifting tasks.

PMID: 11415542 [PubMed - as supplied by publisher]

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14: Spine. 1995 Jun 1;20(11):1271-8; discussion 1278.

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The effect of back belts on lumbar muscle fatigue.

Ciriello VM, Snook SH.

Liberty Mutual Research Center for Safety and Health, Hopkinton, Massachusetts, USA.

STUDY DESIGN. An experiment was conducted to investigate the effect of wearing a weight lifting belt on the endurance and fatigue characteristics of the extensor muscles of the spine. OBJECTIVE. To evaluate the effectiveness of back belts in preserving the endurance characteristics of the spinal musculature. SUMMARY OF BACKGROUND DATA. Previous studies have investigated the use of back belts in increasing intra-abdominal pressure and thus increasing the stabilization of the spine. Other studies have looked at the association of low back disability and wearing back belts. No study has examined the relationship between wearing back belts and measures of spinal muscle fatigue and endurance. METHODS. Thirteen male industrial workers performed a lifting and lowering task from the floor to a 76.2 cm height at 4.3 min-1 2 days a week for 4 weeks. The load was psychophysically determined and averaged 28.1 kg for a total of 28.9 metric tons moved in 4 hours. Subjects lifted for 1, 2, 3, and 4 hours, respectively, for the first 4 days of the experiment. These were considered training days. During the last 4 days, subjects lifted for 4 hours per day; 2 days with a back belt, and 2 days without a back belt. Maximum isokinetic endurance of the extensors was measured for 50 repetitions (5 sets of 10 repetitions) at the end of 4 hours of lifting. Median frequencies of the electromyographic signal from six locations over the back extensors were measured for 30 seconds at 80% of maximum isometric voluntary contraction after 4 hours of lifting. RESULTS. There were no significant differences in maximum isokinetic endurance, or in the slope of median frequency, between lifting with a back belt and lifting without a back belt. Similarly, a modified Borg scale and a postexperiment survey question were unable to distinguish between wearing a back belt and not wearing a back belt. CONCLUSION. There were no significant differences in maximum isokinetic endurance and electromyographic spectral parameters of the back extensor muscles as a result of wearing a back belt during heavy lifting and lowering tasks.

PMID: 7660236 [PubMed - indexed for MEDLINE]

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15: Spine. 1995 Jan 1;20(1):68-73.

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Comment in:

• Spine. 1995 Aug 15;20(16):1847.

The effect of lumbar belts on isolated lumbar muscle. Strength and dynamic capacity.

Reyna JR Jr, Leggett SH, Kenney K, Holmes B, Mooney V.

Department of Orthopaedic Surgery, University of New Mexico.

STUDY DESIGN. This study analyzed the effect of lumbar support belts on functional performance. OBJECTIVE. To compare lumbar muscle strength and lifting capacity with and without a lumbar belt. SUMMARY OF BACKGROUND DATA. Industrialized settings have begun to encourage the use of lumbar support belts for their employees. It is believed that the belts may decrease the risk of injury and enhance the functional performance of the individual. METHODS. Twenty-two subjects (average age, 27.5 years) were tested on four separate days to evaluate the effect of a commercially available belt on isolated lumbar isometric strength and functional dynamic lifting capacity. All subjects had no history of low back problems. The order of testing with and without a belt was randomized for both conditions. On the first 2 days, subjects performed a seven-angle isometric lumbar extension strength test, 1 day with and 1 day without a lumbar belt. On the following 2 days, subjects were tested to evaluate functional capacity with and without a lumbar belt. The functional capacity evaluation was performed by progressively lifting weighted canisters from various levels. Heart rates were monitored to ensure that a maximum effort was achieved over the different days. RESULTS. T tests revealed that isometric lumbar strength and functional lifting capacity was not significantly affected by the belt. CONCLUSION. The use of a lumbar belt does not enhance isometric lumbar muscle strength or dynamic lifting capacity.

Publication Types:

• Clinical Trial
• Randomized Controlled Trial

PMID: 7709282 [PubMed - indexed for MEDLINE]

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16: J Strength Cond Res. 2003 Nov;17(4):634-7.

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Effect of rest interval length on repeated 1 repetition maximum back squats.

Matuszak ME, Fry AC, Weiss LW, Ireland TR, McKnight MM.

Human Performance Laboratories, The University of Memphis, Memphis, Tennessee 38152, USA.

To examine the effects of different rest intervals on the repeatability of 1 repetition maximum (1RM) efforts in the free-weight back squat exercise, 17 weight-trained men served as subjects (mean age 22.0 years). One repetition maximum was tested on each of the first 2 days of testing to establish a stable baseline (1RM = 184.9 kg). Each of the next 3 sessions involved performing 2 1RM back squats, with the rest interval between attempted lifts being either 1, 3, or 5 minutes, assigned in a counterbalanced fashion. For the 1-minute rest interval, 13 of 17 subjects successfully completed the second lift; for the 3-minute rest interval, 16 of 17 were successful; and for the 5-minute rest interval, 15 of 17 were successful. Cochran Q analysis determined no significant difference (p > 0.05) in the ability to repeat a successful maximal-effort back squat when different rest intervals were used. These findings are consistent with the literature for the bench-press exercise and indicate that 1-minute rest intervals are sufficient for recovery between attempted lifts during 1RM testing or training for the free-weight back squat when involving lifters of this caliber.

Publication Types:

• Clinical Trial
• Controlled Clinical Trial

PMID: 14636099 [PubMed - indexed for MEDLINE]

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17: Ergonomics. 1993 Dec;36(12):1489-93.

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The influence of load knowledge on lifting technique.

Butler D, Andersson GB, Trafimow J, Schipplein OD, Andriacchi TP.

Department of Orthopedic Surgery, Rush-Presbyterian-St Luke's Medical Center, Chicago, IL 60612.

The purpose of this study was to analyse the influence of load knowledge on lifting technique. Ten men lifted a box containing either no weight or weights of 150, 250 or 300 N with and without knowledge of what was inside the box. The kinetics and kinematics of the lift were analysed using a force plate, an optoelectronic motion analysis system, and a rigid body link model. At 0 N lifting, the unknown load resulted in a jerk-like motion and a significantly increased peak L5-S1 flexion-extension moment. At 150 N there was also a significant increase in the speed of trunk extension with unknown weights, but the L5-S1 moment remained unchanged. At higher load levels there were only minor differences between lifting techniques when knowing and not knowing the load. We conclude that lifts are approached assuming a certain weight, and that when the assumption is wrong and the load lighter than anticipated lifting is performed with a 'jerking' motion, creating unnecessary loads on the lower back.

Publication Types:

• Research Support, U.S. Gov't, P.H.S.

PMID: 8287855 [PubMed - indexed for MEDLINE]

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18: Ergonomics. 2000 May;43(5):653-68.

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Effect of foot movement and an elastic lumbar back support on spinal loading during free-dynamic symmetric and asymmetric lifting exertions.

Marras WS, Jorgensen MJ, Davis KG.

Department of Industrial, Welding, and Systems Engineering, The Ohio State University, Columbus 43210, USA.

The aim of this study was to assess the effect of an elastic lumbar back support on spinal loading and trunk, hip and knee kinematics while allowing subjects to move their feet during lifting exertions. Predicted spinal forces and moments about the L5/S1 intervertebral disc from a three-dimensional EMG-assisted biomechanical model, trunk position, velocities and accelerations, and hip and knee angles were evaluated as a function of wearing an elastic lumbar back support, while lifting two different box weights (13.6 and 22.7 kg) from two different heights (knee and 10 cm above knee height), and from two different asymmetries at the start of the lift (sagittally symmetric and 60 degrees asymmetry). Subjects were allowed to lift using any lifting style they preferred, and were allowed to move their feet during the lifting exertion. Wearing a lumbar back support resulted in no significant differences for any measure of spinal loading as compared with the no-back support condition. However, wearing a lumbar back support resulted in a modest but significant decrease in the maximum sagittal flexion angle (36.5 to 32.7 degrees), as well as reduction in the sagittal trunk extension velocity (47.2 to 40.2 degrees s(-1)). Thus, the use of the elastic lumbar back support provided no protective effect regarding spinal loading when individuals were allowed to move their feet during a lifting exertion.

Publication Types:

• Clinical Trial
• Randomized Controlled Trial

PMID: 10877482 [PubMed - indexed for MEDLINE]

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19: J Strength Cond Res. 2003 Feb;17(1):68-71.

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Acute effects of plyometric exercise on maximum squat performance in male athletes.

Masamoto N, Larson R, Gates T, Faigenbaum A.

Departments of Exercise Science and Physical Education, and Athletics, University of Massachusetts, Boston, Massachusetts 02125, USA.

This study examines the acute effects of plyometric exercise on 1 repetition maximum (RM) squat performance in trained male athletes. Twelve men (mean age +/- SD: 20.5 +/- 1.4 years) volunteered to participate in 3 testing sessions separated by at least 6 days of rest. During each testing session the 1RM was assessed on back squat exercise. Before all 3 trials subjects warmed up on a stationary cycle for 5 minutes and performed static stretching. Subjects then performed 5 submaximal sets of 1-8 repetitions before attempting a 1RM lift. Subjects rested for at least 4 minutes between 1RM trials. During the first testing session (T1) subjects performed a series of sets with increasing load until their 1RM was determined. During the second and third testing sessions subjects performed in counterbalanced order either 3 double-leg tuck jumps (TJ) or 2 depth jumps (DJ) 30 seconds before each 1RM attempt. The average 1RM lifts after T1 and testing sessions with TJ or DJ were 139.6 +/- 29.3 kg, 140.5 +/- 25.6 kg, and 144.5 +/- 30.2 kg, respectively (T1 < DJ; p < 0.05). These data suggest that DJ performed before 1RM testing may enhance squat performance in trained male athletes.

Publication Types:

• Research Support, Non-U.S. Gov't

PMID: 12580658 [PubMed - indexed for MEDLINE]

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20: Arch Phys Med Rehabil. 2002 Jan;83(1):48-59.

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Balance loss when lifting a heavier-than-expected load: effects of lifting technique.

Heiss DG, Shields RK, Yack HJ.

Physical Therapy Division, College of Medicine and Public Health, Ohio State University, Columbus, OH 43210-1234, USA. Heiss.8@osu.edu

OBJECTIVES: To compare the lifting techniques of subjects who did and did not maintain their balance with an unexpectedly heavy load, and to examine whether the balance loss increased low back loading. DESIGN: Repeated-measures design. SETTING: A research laboratory. PARTICIPANTS: Fourteen healthy volunteers were assigned to 2 groups in the post hoc analysis. Group 1 (7 men; mean age, 25.6 +/- 4.2yr; height, 1.78 +/-.08m; weight, 83.0 +/- 8.5kg; lifting capacity, 63.2 +/- 8.0kg) maintained balance and was matched to group 2 (7 men; mean age, 26.3 +/- 4.1yr; height, 1.75 +/-.06m; weight, 78.2 +/- 5.3kg; lifting capacity, 64.7 +/- 4.9kg) who lost balance. INTERVENTIONS: Subjects lifted boxes of 5%, 20%, and 35% of their lifting capacity. Load magnitude was expected or unexpected. MAIN OUTCOME MEASURES: Center of mass (COM), lower body mechanics, ground reaction forces, and angular and horizontal momentum. RESULTS: Group 1 consistently showed greater lumbar flexion, less knee flexion, and a higher COM just before and after load liftoff. During the heavier-than-expected 35% lift, the trunk angular velocities lifts indicated that both groups experienced eccentric trunk extensor muscle contractions. CONCLUSIONS: The semisquat technique may protect against balance loss when lifting unexpectedly heavy loads. Eccentric muscle contractions and rapid increases in lumbar joint reaction moments may increase the risk of low back injury when there is a large, unexpected increase in the weight of the lifted load. Copyright 2002 by the American Congress of Rehabilitation Medicine and the American Academy of Physical Medicine and Rehabilitation

Publication Types:

• Comparative Study
• Research Support, Non-U.S. Gov't
• Research Support, U.S. Gov't, Non-P.H.S.

PMID: 11782833 [PubMed - indexed for MEDLINE]

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21: Clin Biomech (Bristol, Avon). 2000 Aug;15(7):469-77.

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Lifting an unexpectedly heavy object: the effects on low-back loading and balance loss.

van der Burg JC, van Dieën JH, Toussaint HM.

Faculty of Human Movement Sciences, Institute for Fundamental and Clinical Human Movement Sciences, Vrije Universiteit Amsterdam, Van der Boechorststraat 9, 1081 BT, Amsterdam, Netherlands. pvvanvdervburg@fbw.vu.nl

OBJECTIVE. This study evaluates the effects of lifting an unexpectedly heavy object on low-back loading and loss of balance. BACKGROUND. It is often suggested that lifting an unexpectedly heavy object may be a major risk factor for low-back pain. This may lead to an increase in muscle activation, stretch of ligaments and posterior disc, and loss of balance.METHODS. Nine healthy male subjects were asked to pick up and lift a box as quickly as possible. The weight of the box was unexpectedly increased by 5 or 10 kg. Kinematics and force data were recorded throughout the experiment. RESULTS. Lifting of an unexpectedly heavy box led to a decrease in maximum torque of the low back compared to lifting the same box mass with correct expectation. The maximum lumbar angle did not increase compared to the light box condition. Only the threat to balance appeared to be somewhat increased.CONCLUSIONS. The lifting of an unexpectedly heavier box appeared not to lead to an increased balance loss or a clearly increased stress of the structures of the low back, although a burst of abdominal muscle activity was found in one condition. These results do not fully clarify the assumed relation between lifting unexpectedly heavy objects and low-back injury.RelevanceA commonly cited cause of low-back pain is the lifting of an unexpectedly heavy object. A study of the responses to such perturbation is important to an understanding of spine mechanics and the etiology of low-back injury.

Publication Types:

• Clinical Trial

PMID: 10831806 [PubMed - indexed for MEDLINE]

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22: Hum Factors. 1995 Dec;37(4):844-53.

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Effect of lifting belts, foot movement, and lift asymmetry on trunk motions.

Lavender SA, Thomas JS, Chang D, Andersson GB.

Department of Orthopedic Surgery, Rush-Presbyterian-St. Luke's Medical Center, Chicago, IL 60612, USA.

Whether or not lifting belts protect workers from injury is a topic of considerable interest in industry. Not only is the protective effect uncertain, but the biomechanical basis for belt function is unclear. The objective of this study was to determine if lifting belts provide a means for controlling trunk motions during asymmetric material-handling tasks. We recruited 16 nursing personnel as experienced lifters to participate in two lifting sessions. A lifting belt was worn in one session and for a week prior to this session during the subjects' routine work activities. Each session required 42 lifts, distributed across three asymmetry conditions (0, 45, and 90 deg) and temporally spaced 30 s apart. Foot motion was not permitted in half the lifts. Results indicated that during lifting, lateral bending and twisting motions were reduced by both the lifting belt and foot motion; the most pronounced effect was observed at 90 deg of asymmetry. Trunk motions in the sagittal plane during lifting were not affected by the lifting belt. These results appear to support the use of lifting belts in asymmetric lifting conditions, but more research is needed to determine whether the muscles in the torso benefit from the reduced motion or are working harder to overcome this resistance to motion, causing increased internal loads on the spine during asymmetric material-handling tasks.

Publication Types:

• Clinical Trial
• Randomized Controlled Trial

PMID: 8851780 [PubMed - indexed for MEDLINE]

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23: J Strength Cond Res. 2006 Feb;20(1):145-50.

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The effect of the direction of gaze on the kinematics of the squat exercise.

Donnelly DV, Berg WP, Fiske DM.

Department of Intercollegiate Athletics, Miami University, Oxford, Ohio 45056, USA.

The purpose of this study was to determine whether the direction of gaze influences the kinematics of the squat exercise. Ten men experienced in the squat exercise performed a total of 30 repetitions of the squat in the form of 2 sets of 5 repetitions under 3 different conditions. Conditions varied with respect to the direction of the subjects' gaze as they performed the exercise. Condition D entailed gazing downward at the intersection of the facing wall and the floor throughout the exercise. Condition S required subjects to gaze straight ahead at their own reflection (eyes) in the mirror on the wall directly in front of them. Condition U involved gazing upward at the intersection of the facing wall and the ceiling throughout the exercise. Dependent variables included the linear displacement of the bar and hip, linear velocity of the bar, and the angular displacement/position and velocity of the head, trunk, hip, and knee. The mean data were subjected to a repeated measures analysis of variance, and, where appropriate, pairwise comparisons using Tukey's Studentized Range Test. The results revealed overall similarity in movement kinematics when performing the squat exercise using the 3 different gaze directions. In particular, the upward and straight gaze conditions were not differentiated by the analysis. Conversely, the downward gaze was shown to increase the extent of hip flexion (F[2, 9] = 4.82, p < .05), especially relative to the upward gaze, and possibly trunk flexion as well (F[2, 9] = 3.02, p = .07). In terms of the practical application, because excessive hip and trunk flexion in the squat are contraindicated, cautioning athletes against allowing the head or direction of gaze to drop below a neutral position appears to be warranted.

PMID: 16503674 [PubMed - indexed for MEDLINE]

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24: Am J Occup Ther. 2000 Mar-Apr;54(2):166-75.

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Effects of body mechanics training on performance of repetitive lifting.

Lieber SJ, Rudy TE, Boston JR.

Department of Anesthesiology/CCM, University of Pittsburgh, Pennsylvania 15213, USA. liebersj@peti.sm.upmc.edu

OBJECTIVE: To measure the efficacy of body mechanics instruction (BMI) in patients with low back pain. METHOD: The effect of BMI was measured in four participants with back injuries using a standardized lifting protocol. Static strength, weight lifted, number of lifts completed, and motion analysis data to describe the body mechanics were measured before and after work hardening to evaluate treatment effects. The participants' performances were compared with 52 controls from an earlier study. RESULTS: Starting postures, characterized by degrees of hip and knee flexion, varied by participant but favored a squat lift in three participants when compared with the controls. Dynamic motion synchrony of the hip and knee joints was similar to controls in three of the four participants. Posttest data revealed significant changes in static strength, dynamic endurance, and lifting speed. CONCLUSION: Intensive instruction in body mechanics provided during the work-hardening treatment produced major changes in lifting styles, in terms of both starting postures and dynamic aspects of repetitive lifting. The computerized measurement procedures used in this study permitted more careful and detailed analyses of body mechanics, particularly dynamic aspects, than is possible with observational methods. This study demonstrated some of the inherent intricacies in isodynamic lifting and suggests additional areas of performance that may be important to address in BMI.

Publication Types:

• Comparative Study
• Research Support, U.S. Gov't, P.H.S.

PMID: 10732178 [PubMed - indexed for MEDLINE]

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25: J Sports Sci. 2005 Jul;23(7):687-92.

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Maximal strength and cortisol responses to psyching-up during the squat exercise.

McGuigan MR, Ghiagiarelli J, Tod D.

School of Biomedical and Sports Science, Edith Cowan University, Joondalup, WA, Australia. m.mcguigan@ecu.edu.au

We studied the effect of psyching-up on one-repetition maximum (1-RM) performance and salivary cortisol responses during the squat exercise. Ten men (age 21.6+/-1.4 years; mean+/-s) and ten women (age 22.4+/-2.8 years) with weight training experience of 4.5+/-2.0 years participated in this study. One-repetition maximum squats were performed on a Smith machine during each of two different intervention conditions that were counterbalanced and consisted of a free choice psych-up and a cognitive distraction. Saliva samples were obtained at the beginning of each test session and immediately after the final 1-RM attempt. No significant difference in 1-RM was identified between psyching-up (104+/-50 kg) and cognitive distraction (106+/-52 kg). Performing a 1-RM in the squat exercise significantly increased salivary cortisol concentrations during both conditions (P<0.05). There was no significant difference in salivary cortisol responses between conditions. These results suggest that psyching-up does not increase 1-RM performance during the squat exercise in strength-trained individuals.

Publication Types:

• Comparative Study

PMID: 16195018 [PubMed - indexed for MEDLINE]

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26: Spine. 2002 Jun 1;27(11):1208-12.

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The contribution of aerobic fitness and back strength to lift capacity.

Matheson LN, Leggett S, Mooney V, Schneider K, Mayer J.

Program in Occupational Therapy, Washington University School of Medicine, St. Louis, Missouri, USA. mathesonl@msnotes.wustl.edu

STUDY DESIGN: This study used a concurrent validation design with 45 healthy female participants. OBJECTIVE: To measure the relative contributions of aerobic capacity and back strength to lift capacity. SUMMARY OF BACKGROUND DATA: This was the first concurrent study of the relations among spine strength, aerobic capacity, and lift capacity. Previous research had demonstrated moderate to strong relations between spine strength and lift capacity and between aerobic capacity and lift capacity. METHODS: Multiple regression techniques were used on reliable and valid measures of each construct to study the individual and joint contributions of spine strength and aerobic capacity to lift capacity. RESULTS: Both spine strength and aerobic capacity make significant independent contributions to lift capacity, accounting for 11% and 27% of the variance, respectively. Taken together, the predictive power of these variables on lift capacity accounts for 43% of the variance. CONCLUSIONS: Lift capacity is dependent on both back strength and aerobic capacity. It may be inappropriate to use lift capacity as an indicator for the severity of spine impairment in a disability determination system without taking into account the individual's aerobic capacity. Treatment intended to improve the lift capacity of persons with spine impairment should anticipate that improvement in both back strength and aerobic capacity will improve lift capacity.

Publication Types:

• Clinical Trial

PMID: 12045519 [PubMed - indexed for MEDLINE]

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27: J Sports Med Phys Fitness. 1991 Jun;31(2):154-60.

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Weight training economy as a function of intensity of the squat and overhead press exercise.

Kalb JS, Hunter GR.

Department of Health Education and Physical Education, University of Alabama, Birmingham.

The purpose of this investigation was to study the relationship between exercise intensity and weight training economy. Seven subjects performed squat and seated behind the neck press exercises at 60% and 80% of one repetition maximum (1 RM). Addition of net exercise oxygen uptake (VO2) to net recovery VO2 provided an estimate of metabolic cost for the exercise. Estimation of work performed was accomplished by calculation of vertical external work (VEW). Weight training economy was calculated (weight training economy = kcals consumed x VEW-1). The squat was significantly more economical than the overhead press (p = 0.002), and exercise at 60% 1 RM was more economical than exercise at 80% 1 RM (p less than 0.001). Correlations between VEW and kcals consumed at each intensity ranged between 0.85-0.98. It was determined that estimation of metabolic cost of weight training exercise must take into account not only the vertical external work accomplished, but also the intensity of the exercise (% 1 RM). Vertical external work performed on the bar appears to be as accurate as the total vertical external work value in prediction of metabolic cost of the squat and overhead press exercises. Use of the weight training economy values obtained in this study for prediction of metabolic cost will provide values with 4.2%-15.8% prediction error.

PMID: 1753720 [PubMed - indexed for MEDLINE]

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28: Spine. 2006 Oct 15;31(22):E833-9.

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Effect of a stiff lifting belt on spine compression during lifting.

Kingma I, Faber GS, Suwarganda EK, Bruijnen TB, Peters RJ, van Dieën JH.

Institute of Fundamental and Clinical Human Movement Sciences, Faculty of Human Movement Sciences, Vrije Universiteit, Amsterdam, Netherlands. I_KINGMA@FBW.VU.NL

STUDY DESIGN: An in vivo study on weightlifters. OBJECTIVES: To determine if and how a stiff back belt affects spinal compression forces in weightlifting. SUMMARY OF BACKGROUND DATA: In weightlifting, a back belt has been reported to enhance intraabdominal pressure (IAP) and to reduce back muscle EMG and spinal compression forces. METHODS: Nine experienced weightlifters lifted barbells up to 75% body weight while inhaling and wearing a belt, inhaling and not wearing a belt, and exhaling and wearing a belt. IAP, trunk muscle EMG, ground reaction forces, and kinematics were measured. An EMG-assisted trunk model, including IAP effects, was used to calculate spinal compression and shear forces and to reveal the contribution of back muscles, abdominal muscles, and IAP to moment generation. RESULTS: The belt reduced compression forces by about 10%, but only when inhaling before lifting. The moment generated by IAP increased when wearing a belt and inhaling, but this moment was small and the increase was largely negated by the flexing moment generated by abdominal muscles. CONCLUSIONS: Wearing a tight and stiff back belt while inhaling before lifting reduces spine loading. This is caused by a moment generated by the belt rather than by the IAP.

PMID: 17047531 [PubMed - indexed for MEDLINE]

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29: Arch Phys Med Rehabil. 1995 May;76(5):457-62.

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Influence of breathing technique on arterial blood pressure during heavy weight lifting.

Narloch JA, Brandstater ME.

Department of Physical Medicine and Rehabilitation, Loma Linda University, CA 92354.

Arterial hypertension occurring during heavy resistance exercise may be a risk factor for stroke in healthy young adults. Any training method that ameliorates the pressor effect of exercise should reduce the risk of stroke. The objective of this study was to observe the influence of breathing technique on arterial blood pressure (BP) generated during heavy, dynamic weight lifting. BP was recorded in 10 male athletes by radial artery catheterization. Each subject then performed double-leg press sets at 85% and 100% of maximum. Each exercise was performed twice, once with closed glottis Valsalva, and then with slow exhalation during concentric contraction. The mean BP at 100% maximum with Valsalva was 311/284. The highest pressure recorded in an individual was 370/360. With slow exhalation, the mean BP was 198/175 when the same 100% maximum was lifted (p < .005). A reduced pressor response was also noted at 85% maximal lifting with slow exhalation. Arterial hypertension produced during heavy weight lifting with Valsalva is extreme and may be dramatically reduced when the exercise is performed with an open glottis (without Valsalva). It is concluded that heavy resistance exercise is safer when performed while the subject breathes with an open glottis.

Publication Types:

• Comparative Study

PMID: 7741618 [PubMed - indexed for MEDLINE]

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30: J Orthop Sports Phys Ther. 2000 May;30(5):237-47; discussion 258-61.

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Relationship between lifting capacity and anthropometric measures.

Gross MT, Dailey ES, Dalton MD, Lee AK, McKiernan TL, Vernon WL, Walden AC.

Program in Human Movement Science, Division of Physical Therapy, The University of North Carolina at Chapel, 27599-7135, USA mgross@css.unc.edu

STUDY DESIGN: Prospective analysis of relationship between lifting capacity and multiple anthropometric variables. OBJECTIVES: To determine the relationship between lifting capacity and anthropometric variables and to model this relationship quantitatively. BACKGROUND: Low-back injuries commonly occur in individuals who perform lifting tasks. Objective data are needed to determine preinjury lifting capacity that, in turn, might be used to guide decisions during rehabilitation of these injuries. METHODS AND MEASURES: We recorded age and sex and measured the following variables for 35 men and 23 women between the ages of 22 and 40: height, weight, percentage of body fat, torso height, pelvic width, pelvic girth, arm length, thigh girth, and calf girth. Variables were selected for the study on the basis of theoretical modeling or previous research regarding the relationship between study variables and lifting capacity. Subjects also were tested to determine their maximum lifting capacity by using a lordotic lumbar spine lifting technique. RESULTS: Stepwise regression analysis indicated that the combination of sex, age, thigh girth, pelvic girth, and percentage body fat was significantly related to maximum lift capacity (multiple R2 = 0.76). The mean absolute difference (+/- SD) between lifted amount predicted by the regression model and the actual amount lifted was 118.6 +/- 86 N (26 +/- 19.3 lb), which corresponded to an average absolute error of 16% (SD = 14%) of the actual weight lifted. CONCLUSION: The results may be useful in estimating 1 aspect of preinjury lifting capacity. Similar studies are needed to model the requirements of frequency of lift, duration of lifting efforts, variety of hand-object coupling, and combined lifting and reaching.

Publication Types:

• Comparative Study

PMID: 10817411 [PubMed - indexed for MEDLINE]

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31: Med Sci Sports Exerc. 1989 Jun;21(3):299-303.

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The effect of the squat exercise on knee stability.

Chandler TJ, Wilson GD, Stone MH.

Department of Health and Human Performance, Auburn University, AL 36849.

Past studies have produced conflicting results as to the effect of squat exercises on knee stability. One hundred male and female college students were measured using a knee ligament arthrometer on nine tests of knee stability. Over an 8-wk training program, full or half squats did not consistently affect knee stability compared to non-squatting controls. To measure the effect of long-term squat training 27 male powerlifters (14 Elite or Master Class) and 28 male weightlifters (8 Elite or Master Class) were measured on the same tests. Powerlifters were significantly tighter than controls on the anterior drawer at 90 degrees of knee flexion. Both powerlifters and weightlifters were significantly tighter than controls on the quadriceps active drawer at 90 degrees of knee flexion. Data on powerlifters and weightlifters were also analyzed by years of experience and skill level. No effect of squat training on knee stability was demonstrated in any of the groups tested.

PMID: 2733579 [PubMed - indexed for MEDLINE]

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32: Res Q Exerc Sport. 1997 Mar;68(1):56-61.

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Learning versus correct models: influence of model type on the learning of a free-weight squat lift.

McCullagh P, Meyer KN.

Department of Kinesiology, University of Colorado-Boulder, USA. mccullagh@colorado.edu

It has been assumed that demonstrating the correct movement is the best way to impart task-relevant information. However, empirical verification with simple laboratory skills has shown that using a learning model (showing an individual in the process of acquiring the skill to be learned) may accelerate skill acquisition and increase retention more than using a correct model. The purpose of the present study was to compare the effectiveness of viewing correct versus learning models on the acquisition of a sport skill (free-weight squat lift). Forty female participants were assigned to four learning conditions: physical practice receiving feedback, learning model with model feedback, correct model with model feedback, and learning model without model feedback. Results indicated that viewing either a correct or learning model was equally effective in learning correct form in the squat lift.

PMID: 9094763 [PubMed - indexed for MEDLINE]

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33: Br J Sports Med. 1979 Jun;13(2):58-61.

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A study of changes in the spine in weight lifters and other athletes.

Aggrawal ND, Kaur R, Kumar S, Mathur DN.

The present study was undertaken in sportsmen of those groups of sports activities where weight training exercises constitute a major part of the training. Two groups consisting of 25 weight-lifters and 25 track and field athletes were studied to find out the effect of sports activities and lifting weights on the spine. 84% weight-lifters and 72% track and field athletes suffered from varying abnormalities. Incidence of backache in 25 weight-lifters was 40% and in 25 track and field athletes 48%. Radiological changes were more common in weight-lifters (84%) than in athletes (72%). Reduction in lumbar lordosis was found in three cases (12%) in both the groups. Obtuse angle deformity of vertebral margins was found in 11 cases (44%) amongst weight-lifters and six cases (24%) amongst athletes. Osteophytic formation was found in six cases (24%) in weight-lifters and four cases (16%) in athletes. Schmorl's node were noticed in five cases (20%) amongst weight-lifters and seven cases (28%) amongst athletes. The incidences of spondylosis and Schmorl's node were found only in those cases who had been doing weight training exercises for more than four years.

PMID: 157179 [PubMed - indexed for MEDLINE]

PMCID: PMC1859682

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34: Clin Biomech (Bristol, Avon). 1999 Dec;14(10):685-96.

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Stoop or squat: a review of biomechanical studies on lifting technique.

van Dieën JH, Hoozemans MJ, Toussaint HM.

Amsterdam Spine Unit, Institute for Fundamental and Clinical Human Movement Sciences, Faculty of Human Movement Sciences, Vrije Universiteit, Amsterdam, The Netherlands. j_h_van_dieen@fbw.vu,nl

OBJECTIVE: To assess the biomechanical evidence in support of advocating the squat lifting technique as an administrative control to prevent low back pain. BACKGROUND: Instruction with respect to lifting technique is commonly employed to prevent low back pain. The squat technique is the most widely advised lifting technique. Intervention studies failed to show health effects of this approach and consequently the rationale behind the advised lifting techniques has been questioned. METHODS: Biomechanical studies comparing the stoop and squat technique were systematically reviewed. The dependent variables used in these studies and the methods by which these were measured or estimated were ranked for validity as indicators of low back load. RESULTS: Spinal compression as indicated by intra-discal pressure and spinal shrinkage appeared not significantly different between both lifting techniques. Net moments and compression forces based on model estimates were found to be equal or somewhat higher in squat than in stoop lifting. Only when the load could be lifted from a position in between the feet did squat lifting cause lower net moments, although the studies reporting this finding had a marginal validity. Shear force and bending moments acting on the spine appeared lower in squat lifting. Net moments and compression forces during lifting reach magnitudes, that can probably cause injury, whereas shear forces and bending moments remained below injury threshold in both techniques. CONCLUSION: The biomechanical literature does not provide support for advocating the squat technique as a means of preventing low back pain.RELEVANCE: Training in lifting technique is widely used in primary and secondary prevention of low back pain, though health effects have not been proven. The present review assesses the biomechanical evidence supporting the most widely advocated lifting technique.

Publication Types:

• Meta-Analysis

PMID: 10545622 [PubMed - indexed for MEDLINE]

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35: Ergonomics. 2001 Feb 10;44(2):202-14.

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Gender differences in lifting technique.

Lindbeck L, Kjellberg K.

The National Institute for Working Life, Stockholm, Sweden. Lars.Lindbeck@niwl.se

The importance of different motion patterns in the assessment of work technique is rarely addressed in the literature and even less information can be found regarding gender differences. In this study the possible gender differences in lifting technique from lifting experiments on 12 female and 10 male participants were examined. The participants performed squat and stoop lifts of a box. Movements were measured by means of opto-electronic measurement systems. Kinematic data derived from the measurements revealed some differences between the men and the women, e.g. in trunk motion and knee angle ranges. The hip-knee interjoint coordination was more synchronized for women than for men in terms of the relative phase angle. It is concluded that so far gender differences in motion patterns have not been sufficiently explored and that men and women need to be considered separately in the evaluation of work technique in manual handling tasks. Advantages and disadvantages of different coordination patterns need to be further investigated.

Publication Types:

• Research Support, Non-U.S. Gov't

PMID: 11209877 [PubMed - indexed for MEDLINE]

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36: Spine. 2004 Feb 15;29(4):464-9.

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The effects of breath control on intra-abdominal pressure during lifting tasks.

Hagins M, Pietrek M, Sheikhzadeh A, Nordin M, Axen K.

Division of Physical Therapy, Long Island University, Brooklyn, New York 11201, USA. mhagins@liu.edu

STUDY DESIGN: This was a repeated measures study examining 11 asymptomatic subjects while performing dynamic lifting using various postures, loads, and breath control methods. OBJECTIVES: To examine the effects of breath control on magnitude and timing of intra-abdominal pressure during dynamic lifting. SUMMARY OF BACKGROUND DATA: Intra-abdominal pressure has been shown to increase consistently during static and dynamic lifting tasks. The relationship between breath control and intra-abdominal pressure during lifting is not clear. METHODS: Eleven healthy subjects were tested using lifting trials consisting of two levels of posture and load and four levels of breath control (natural breathing, inhalation-hold, exhalation-hold, inhalation-exhalation). Intra-abdominal pressure was measured using a microtip pressure transducer placed within the stomach through the nose. Timing of intra-abdominal pressure was determined relative to lift-off of the weights. Repeated measures analysis of variance was used to determine the effect of breath control, posture, and load on intra-abdominal pressure magnitude and timing. RESULTS: There was a significant effect of breath control (P < 0.018) and load (P < 0.002), but not of posture (P < 0.434), on intra-abdominal pressure magnitude. The inhalation-hold form of breath control produced significantly greater peak intra-abdominal pressure than all other forms of breath control (P < 0.000 for all comparisons). No other comparisons among levels of breath were significantly different. No significant main effects of breath control were found relative to intra-abdominal pressure timing. CONCLUSIONS: Breath control is a significant factor in the generation of intra-abdominal pressure magnitude during lifting tasks. The effects of respiration should be controlled in studies analyzing intra-abdominal pressure during lifting.

PMID: 15094544 [PubMed - indexed for MEDLINE]

Power-time, force-time, and velocity-time curve analysis during the jump squat: impact of load.

Cormie P, McBride JM, McCaulley GO.

School of Exercise, Biomedical and Health Sciences, Edith Cowan University, Perth, Western Australia.

The purpose of this investigation was to examine the impact of load on the power-, force- and velocity-time curves during the jump squat. The analysis of these curves for the entire movement at a sampling frequency of 200-500 Hz averaged across 18 untrained male subjects is the most novel aspect of this study. Jump squat performance was assessed in a randomized fashion across five different external loads: 0, 20, 40, 60, and 80 kg (equivalent to 0 +/- 0, 18 +/- 4, 37 +/- 8, 55 +/- 12, 74 +/- 15% of 1RM, respectively). The 0-kg loading condition (i.e., body mass only) was the load that maximized peak power output, displaying a significantly (p <or=.05) greater value than the 40, 60, and 80 kg loads. The shape of the force-, power-, and velocity-time curves changed significantly as the load applied to the jump squat increased. There was a significantly greater rate of power development in the 0 kg load in comparison with all other loads examined. As the first comprehensive illustration of how the entire power-, force-, and velocity-time curves change across various loading conditions, this study provides extensive evidence that a load equaling an individuals body mass (i.e., external load = 0 kg) maximizes power output in untrained individuals during the jump squat.

PMID: 18579903 [PubMed - in process]

 

2: J Strength Cond Res. 2008 Mar;22(2):567-74.

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The effects of combining elastic and free weight resistance on strength and power in athletes.

Anderson CE, Sforzo GA, Sigg JA.

Exercise and Sport Sciences, Ithaca College, Ithaca, New York, USA.

This study was undertaken to determine whether combined elastic and free weight resistance (CR) provides different strength and power adaptations than free weight resistance (FWR) training alone. Forty-four young (age 20 +/- 1 years), resistance-trained (4 +/- 2 years' experience) subjects were recruited from men's basketball and wrestling teams and women's basketball and hockey teams at Cornell University. Subjects were stratified according to team, then randomly assigned to the control (C; n = 21) or experimental group (E; n = 23). Before and after 7 weeks of resistance training, subjects were tested for lean body mass, 1 repetition maximum back squat and bench press, and peak and average power. Both C and E groups performed identical workouts except that E used CR (i.e., elastic resistance) for the back squat and bench press, whereas the C group used FWR alone. CR was performed using an elastic bungee cord attached to a standard barbell loaded with plates. Elastic tension was accounted for in an attempt to equalize the total work done by each group. Statistical analyses revealed significant (P < 0.05) between-group differences after training. Compared with C, improvement for E was nearly three times greater for back squat (16.47 +/- 5.67 vs. 6.84 +/- 4.42 kg increase), two times greater for bench press (6.68 +/- 3.41 vs. 3.34 +/- 2.67 kg increase), and nearly three times greater for average power (68.55 +/- 84.35 vs. 23.66 +/- 40.56 watt increase). Training with CR may be better than FWR alone for developing lower and upper body strength, and lower body power in resistance-trained individuals. Long-term effects are unclear, but CR training makes a meaningful contribution in the short term to performance adaptations of experienced athletes.

PMID: 18550975 [PubMed - in process]

 

3: J Strength Cond Res. 2008 Mar;22(2):433-46.

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Force-time curve characteristics and hormonal alterations during an eleven-week training period in elite women weightlifters.

Haff GG, Jackson JR, Kawamori N, Carlock JM, Hartman MJ, Kilgore JL, Morris RT, Ramsey MW, Sands WA, Stone MH.

Division of Exercise Science, West Virginia University School of Medicine, Morgantown, West Virginia, USA. ghaff@hsc.wvu.edu

The purpose of this investigation was to study the effects of an 11-week training period performed by female weightlifters. Two weeks before this investigation, baseline measures for total testosterone, cortisol, and testosterone:cortisol ratio were collected. The 11-week training program consisted of the core exercises (i.e., clean, clean and jerk, and snatch) and other supplemental exercises (i.e., clean pull, snatch pull, squat, and front squat). Hormonal, isometric, and dynamic middle thigh pull force-time curve characteristics were assessed biweekly throughout the duration of the investigation, whereas volume load and training intensity were assessed weekly throughout the investigation. The testosterone:cortisol ratio of the baseline (1.19 +/- 0.64) was significantly different from the ratio of weeks 1 (0.67 +/- 0.36) and 9 (0.94 +/- 0.66). When the week-to-week values were compared, week 1 (0.67 +/- 0.36) was significantly different (P < 0.05; eta = 0.84) from week 3 (1.06 +/- 0.54). A very strong correlation (r = -0.83; r = 0.69) was found between the percentage change of the testosterone:cortisol ratio and volume load from weeks 1 to 11. Moderate to very strong correlations were noted between the percentage change in volume load and isometric peak force, peak force during the 30% isometric peak force trial, and peak force during the 100-kg trial during the 11 weeks of training. The primary finding of this study was that alterations in training volume load can result in concomitant changes in the anabolic-to-catabolic balance, as indicated by the testosterone:cortisol ratio, and the ability to generate maximal forces.

PMID: 18550958 [PubMed - in process]

 

4: J Strength Cond Res. 2008 Jul;22(4):1164-8.

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Online weight training.

McNamara JM, Swalm RL, Stearne DJ, Covassin TM.

Department of Physical Education, St. Francis College, Brooklyn Heights, New York, USA. jmcnamara@stfranciscollege.edu

The purpose of this study was to determine how a traditional weight training class compared to nontraditional classes that were heavily laden with technology. Could students learn resistance exercises by watching video demonstrations over the Internet? Three university weight training classes, each lasting 16 weeks, were compared. Each class had the same curriculum and workout requirements but different attendance requirements. The online group made extensive use of the Internet and was allowed to complete the workouts on their own at any gym that was convenient for them. Seventy-nine college-aged students were randomized into 3 groups: traditional (n = 27), hybrid (n = 25), and online (n = 27). They completed pretest and posttest measures on upper-body strength (i.e., bench press), lower-body strength (i.e., back squat), and knowledge (i.e., written exam). The results indicated that all 3 groups showed significant improvement in knowledge (p < 0.05). The online group did not require the students to attend class and may have resulted in significantly lower scores on the bench press (p < 0.05) and squats (p < 0.05). This study indicates that an online weight training course may improve knowledge but not strength. Possible reasons for a lack of improvement in the online group included lack of motivation, low accountability, and the possibility that the self-reported workouts were not accurate. These results suggest that there is a limit to how much technology can be used in a weight training class. If this limit is exceeded, some type of monitoring system appears necessary to ensure that students are actually completing their workouts.

PMID: 18545193 [PubMed - in process]

 

5: J Orthop Res. 2008 Jun 3. [Epub ahead of print]

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The influence of femoral internal and external rotation on cartilage stresses within the patellofemoral joint.

Besier TF, Gold GE, Delp SL, Fredericson M, Beaupré GS.

Department of Orthopedics, Sports Medicine Center, Arrillaga Recreation Center, 341 Galvez Street, Stanford University, Stanford, California 94305‐6175.

Internal and external rotation of the femur plays an important role in defining the orientation of the patellofemoral joint, influencing contact areas, pressures, and cartilage stress distributions. The purpose of this study was to determine the influence of femoral internal and external rotation on stresses in the patellofemoral cartilage. We constructed finite element models of the patellofemoral joint using magnetic resonance (MR) images from 16 volunteers (8 male and 8 female). Subjects performed an upright weight-bearing squat with the knee at 60 degrees of flexion inside an open-MR scanner and in a gait laboratory. Quadriceps muscle forces were estimated for each subject using an electromyographic-driven model and input to a finite element analysis. Hydrostatic and octahedral shear stresses within the cartilage were modeled with the tibiofemoral joint in a "neutral" position and also with the femur rotated internally or externally by 5 degrees increments to +/-15 degrees . Cartilage stresses were more sensitive to external rotation of the femur, compared with internal rotation, with large variation across subjects. Peak patellar shear stresses increased more than 10% with 15 degrees of external rotation in 75% of the subjects. Shear stresses were higher in the patellar cartilage compared to the femoral cartilage and patellar cartilage stresses were more sensitive to femoral rotation compared with femoral cartilage stress. Large variation in the cartilage stress response between individuals reflects the complex nature of the extensor mechanism and has clinical relevance when considering treatment strategies designed to reduce cartilage stresses by altering femoral internal and external rotation. (c) 2008 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res.

PMID: 18524000 [PubMed - as supplied by publisher]

 

6: J Int Soc Sports Nutr. 2006 Dec 13;3:12-8.

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Effect of protein intake on strength, body composition and endocrine changes in strength/power athletes.

Hoffman JR, Ratamess NA, Kang J, Falvo MJ, Faigenbaum AD.

The College of New Jersey, Ewing, NJ. hoffmanj@tcnj.edu.

ABSTRACT : Comparison of protein intakes on strength, body composition and hormonal changes were examined in 23 experienced collegiate strength/power athletes participating in a 12-week resistance training program. Subjects were stratified into three groups depending upon their daily consumption of protein; below recommended levels (BL; 1.0 - 1.4 g.kg-1.day-1; n = 8), recommended levels (RL; 1.6 - 1.8 g.kg-1.day-1; n = 7) and above recommended levels (AL; > 2.0 g.kg-1.day-1; n = 8). Subjects were assessed for strength [one-repetition maximum (1-RM) bench press and squat] and body composition. Resting blood samples were analyzed for total testosterone, cortisol, growth hormone, and insulin-like growth factor. No differences were seen in energy intake (3,171 +/- 577 kcal) between the groups, and the energy intake for all groups were also below the recommended levels for strength/power athletes. No significant changes were seen in body mass, lean body mass or fat mass in any group. Significant improvements in 1-RM bench press and 1-RM squat were seen in all three groups, however no differences between the groups were observed. Subjects in AL experienced a 22% and 42% greater change in Delta 1-RM squat and Delta 1-RM bench press than subjects in RL, however these differences were not significant. No significant changes were seen in any of the resting hormonal concentrations. The results of this study do not provide support for protein intakes greater than recommended levels in collegiate strength/power athletes for body composition improvements, or alterations in resting hormonal concentrations.

PMID: 18500968 [PubMed - in process]

PMCID: PMC2129168

 

7: J Strength Cond Res. 2008 May;22(3):874-82.

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Effect of a pre-exercise energy supplement on the acute hormonal response to resistance exercise.

Hoffman JR, Ratamess NA, Ross R, Shanklin M, Kang J, Faigenbaum AD.

Department of Health and Exercise Science, College of New Jersey, Ewing, New Jersey, USA. hoffmanj@tcnj.edu

The effect of a pre-exercise energy sport drink on the acute hormonal response to resistance exercise was examined in eight experienced resistance trained men. Subjects were randomly provided either a placebo (P: maltodextrin) or the supplement (S: combination of branched chain amino acids, creatine, taurine, caffeine, and glucuronolactone). Subjects performed 6 sets of no more than 10 repetitions of the squat exercise at 75% of their 1 repetition maximum (1RM) with 2 minutes of rest between sets. Blood draws occurred at baseline pre-exercise, immediately post- (IP), 15 minutes post- (15P), and 30-minutes post (30P) exercise for measurement of serum growth hormone, total and free testosterone, cortisol, and insulin concentrations. Although significant differences were seen only at set 5, the total number of repetitions and training volume tended (p = 0.08) to be higher with S compared to P. Serum growth hormone and insulin concentrations were significantly higher at 15P and IP, respectively, in S compared to P. Results suggest that a pre-exercise energy S consumed 10 minutes before resistance exercise can enhance acute exercise performance by increasing the number of repetitions performed and the total volume of exercise. The enhanced exercise performance resulted in a significantly greater increase in both growth hormone and insulin concentrations, indicating an augmented anabolic hormone response to this pre-exercise S.

Publication Types:

• Research Support, Non-U.S. Gov't

PMID: 18438227 [PubMed - in process]

 

8: J Sport Rehabil. 2008 Feb;17(1):1-10.

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Vastus medialis activation during knee extension exercises: evidence for exercise prescription.

Bolgla LA, Shaffer SW, Malone TR.

Medical College of Georgia, Dept of Phys Therapy, Augusta, GA, USA. LBolgla@mail.mcg.edu

CONTEXT: Knee extension exercise is an important part of knee rehabilitation. Clinicians prescribe non-weight bearing exercise initially and progress patients to weight bearing exercise once they can perform a straight leg raise (SLR). OBJECTIVE: Compare VM activation during a SLR and weight bearing exercises. DESIGN: One-way repeated measures design. Setting: University Laboratory. SUBJECTS: Fifteen healthy subjects. INTERVENTION: One SLR exercise and 6 weight-bearing knee extension exercises. MAIN OUTCOME MEASURES: Electromyographic amplitudes for the VM expressed as a percent maximum voluntary isometric contraction. RESULTS: The SLR had greater activation than the single leg stance and bilateral squat exercises. The step-up and unilateral leg press exercises had the greatest activation. CONCLUSIONS: SLR performance can be an important indicator for exercise progression. These results provide foundational knowledge to assist clinicians with exercise prescription.

Publication Types:

• Comparative Study

PMID: 18270382 [PubMed - indexed for MEDLINE]

 

9: J Strength Cond Res. 2007 Nov;21(4):1146-54.

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The acute effects of twenty-four hours of sleep loss on the performance of national-caliber male collegiate weightlifters.

Blumert PA, Crum AJ, Ernsting M, Volek JS, Hollander DB, Haff EE, Haff GG.

Exercise Physiology Laboratory, Midwestern State University, Wichita Falls, Texas 76308, USA.

Currently, the degree to which sleep loss influences weightlifting performance is unknown. This study compared the effects of 24 hours of sleep loss on weightlifting performance and subjective ratings of psychological states pre-exercise and postexercise in national-caliber male collegiate weightlifters. Nine males performed a maximal weightlifting protocol following 24 hours of sleep loss and a night of normal sleep. The subjects participated in a randomized, counterbalanced design with each sleep condition separated by 7 days. Testosterone and cortisol levels were quantified prior to, immediately after, and 1 hour after the resistance training session. Additionally, profile of mood states and subjective sleepiness were evaluated at the same time points. The resistance training protocol consisted of several sets of snatches, clean and jerks, and front squats. Performance was evaluated as individual exercise volume load, training intensity and overall workout volume load, and training intensity. During each training session the maximum weight lifted for the snatch, clean and jerk, and front squat were noted. No significant differences were found for any of the performance variables. A significant decrease following the sleep condition was noted for cortisol concentration immediately after and 1 hour postexercise. Vigor, fatigue, confusion, total mood disturbance, and sleepiness were all significantly altered by sleep loss. These data suggest that 24 hours of sleep loss has no adverse effects on weightlifting performance. If an athlete is in an acute period of sleep loss, as noticed by negative mood disturbances, it may be more beneficial to focus on the psychological (motivation) rather than the physiological aspect of the sport.

Publication Types:

• Research Support, Non-U.S. Gov't

PMID: 18076267 [PubMed - in process]

 

10: Med Sci Sports Exerc. 2007 Oct;39(10):1817-24.

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Effect of hydration state on strength, power, and resistance exercise performance.

Judelson DA, Maresh CM, Farrell MJ, Yamamoto LM, Armstrong LE, Kraemer WJ, Volek JS, Spiering BA, Casa DJ, Anderson JM.

Human Performance Laboratory, Department of Kinesiology, University of Connecticut, Storrs, CT, USA. djudelson@fullerton.edu

PURPOSE: Although many studies have attempted to examine the effect of hypohydration on strength, power, and high-intensity endurance, few have successfully isolated changes in total body water from other variables that alter performance (e.g., increased core temperature), and none have documented the influence of hypohydration on an isotonic, multiset, multirepetition exercise bout typical of resistance exercise training. Further, no investigations document the effect of hypohydration on the ability of the central nervous system to stimulate the musculature, despite numerous scientists suggesting this possibility. The purposes of this study were to examine the isolated effect of hydration state on 1) strength, power, and the performance of acute resistance exercise, and 2) central activation ratio (CAR). METHODS: Seven healthy resistance-trained males (age = 23 +/- 4 yr, body mass = 87.8 +/- 6.8 kg, body fat = 11.5 +/- 5.2%) completed three resistance exercise bouts in different hydration states: euhydrated (EU), hypohydrated by approximately 2.5% body mass (HY25), and hypohydrated by approximately 5.0% body mass (HY50). Investigators manipulated hydration status via exercise-heat stress and controlled fluid intake 1 d preceding testing. RESULTS: Body mass decreased 2.4 +/- 0.4 and 4.8 +/- 0.4% during HY25 and HY50, respectively. No significant differences existed among trials in vertical jump height, peak lower-body power (assessed via jump squat), or peak lower-body force (assessed via isometric back squat). CAR tended to decrease as hypohydration increased (EU = 95.6 +/- 4.9%, HY25 = 94.0 +/- 3.1%, HY50 = 92.5 +/- 5.1%; P = 0.075, eta(p)(2) = 0.41). When evaluated as a function of the percentage of total work completed during a six-set back squat protocol, hypohydration significantly decreased resistance exercise performance during sets 2-3 and 2-5 for HY25 and HY50, respectively. CONCLUSION: These data indicate that hypohydration attenuates resistance exercise performance; the role of central drive as the causative mechanism driving these responses merits further research.

Publication Types:

• Research Support, Non-U.S. Gov't

PMID: 17909410 [PubMed - indexed for MEDLINE]

 

11: Med Sci Sports Exerc. 2007 Aug;39(8):1291-301.

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Effect of explosive versus slow contractions and exercise intensity on energy expenditure.

Mazzetti S, Douglass M, Yocum A, Harber M.

Human Performance Center, Anderson University, Anderson, IN, USA. samazzetti@salisbury.edu

OBJECTIVE: The primary purpose of this study was to compare the effects of explosive versus slow contractions on the rate of energy expenditure during and after resistance exercise. METHODS: Nine men (20 +/- 2.5 yr) performed three exercise protocols using a plate-loaded squat machine, and a no-exercise (CONTROL) session in a randomly assigned, counterbalanced order. Subjects performed squats using either two second (SLOW) or explosive concentric contractions (EXPL), but identical repetitions (8), sets (4), and loads (60% 1RM). A secondary objective was to compare high- versus moderate-intensity exercise. Thus, a third protocol was performed that also used explosive contractions, with heavier loads (80% 1RM) and six sets of four reps (HEAVYEXPL). Eccentric reps (2 s), work (reps x sets x load), range of motion, and rest intervals between sets (90 s) were identical among all three protocols. Expired air was collected continuously for 20 min before, during, and 1 h after exercise and for about 1.5 h during CONTROL. Blood samples (25 microL) were collected before, immediately after, and 15, 30, 45, and 60 min after each protocol, and these samples were analyzed for blood lactate (mM). RESULTS: Average rates of energy expenditure (kcal.min) were significantly greater (P <or= 0.05) during (7.27 +/- 2.00 > 6.43 +/- 1.64 and 6.25 +/- 1.55, respectively) and after (2.54 +/- 1.44 > 2.38 +/- 1.31 and 2.21 +/- 1.08, respectively) EXPL compared with SLOW and HEAVYEXPL, despite significantly (P <or= 0.05) greater blood lactate after SLOW. CONCLUSION: Squat exercise using explosive contractions and moderate intensity induced a greater increase in the rate of energy expenditure than squats using slow contractions or high intensity in all subjects tested. Thus, by using explosive contractions and moderate exercise intensity, experienced recreational exercisers can increase their energy expenditure during and after resistance exercise, and this could enhance weight-loss adaptations.

Publication Types:

• Randomized Controlled Trial
• Research Support, Non-U.S. Gov't

PMID: 17762362 [PubMed - indexed for MEDLINE]

 

12: Br J Sports Med. 2008 Feb;42(2):99-102; discussion 102. Epub 2007 Jul 5.

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Open versus closed kinetic chain exercises for patellar chondromalacia.

Bakhtiary AH, Fatemi E.

Physiotherapy Department, Rehabilitation Faculty, Semnan University of Medical Sciences, Semnan, Iran. amir822@yahoo.com

SUBJECT: Conservative treatment of patellar chondromalacia has been the subject of several studies. One recommended treatment is a strengthening exercise of the quadriceps muscle, which may be performed in closed or open kinetic chains. This study was designed to compare the effect of straight leg raise (SLR) and semi-squat exercises on the treatment of patellar chondromalacia, which has not been done to date. MATERIAL AND METHODS: 32 female university students with a diagnosis of patellar chondromalacia were randomly assigned to two experimental groups: SLR and semi-squat exercise. Before starting exercise protocols, Q angle, maximal isometric voluntary contraction force (MIVCF) of quadriceps, crepitation, circumference of thigh 5 and 10 cm above the patella and patellofemoral pain according to the visual analogue scale (VAS) were assessed. Both groups then followed a 3-week programme of quadriceps muscle strengthening exercises (SLR or semi-squat) starting with 20 exercises twice a day and increasing each session by 5 exercises every 2 days. All measurements were repeated at the end of each week and then again 2 weeks after the 3-week exercise programme. RESULTS: Reduced Q angle (mean differences (SD) 0.8 (0.3), p = 0.016) and crepitation (19.9 (8.5), p = 0.04), and an increase in the MIVCF of the quadriceps (15.8 (5.6), p = 0.01) and thigh circumference (1.5 (0.3), p = 0.001) were found in semi-squat group compared with SLR group. However, patellofemoral pain was decreased significantly in both groups. CONCLUSION: The results of this study indicate that semi-squat exercises (closed kinetic chain) are more effective than SLR exercise (open kinetic chain) in the treatment of patellar chondromalacia. More studies are needed to investigate the long-term effect of these types of exercise.

Publication Types:

• Comparative Study
• Randomized Controlled Trial
• Research Support, Non-U.S. Gov't

PMID: 17615174 [PubMed - indexed for MEDLINE]

 

13: Int J Sports Med. 2008 Mar;29(3):225-31. Epub 2007 Jul 5.

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Coordination specificity in strength and power training.

Leirdal S, Roeleveld K, Ettema G.

Human Movement Science, NTNU, Trondheim, Norway. stig.leirdal@svt.ntnu.no

In this study, we tested the hypothesis that specificity of inter-joint coordination in power training improves training effects. We compared two different training regimes, one with and one without the possibility to exploit the coordination between knee and ankle, on performance and coordination in maximal vertical jumping and explosive squat movements. 22 subjects were divided into two groups for a 5-week training study. One group (Tsingle) trained squats (SQ) and plantar flexions (PL) in separate activities and the other group (Tmulti) trained squats ending with plantar flexion in one movement (SQPL), three times a week. Both groups increased their peak power during training movements between 2 - 15 % (depending on the training movement) but there were no group effects. There were no effects on vertical jumping performance. However, our data indicate different coordinative changes between groups in the vertical jump after the training period. The group specific training movements resulted in an increased power potential that is shown in the training movements themselves but did not transfer to an increased vertical jump performance in either group. However, some training movement specific coordination effects were seen during vertical jumping. In this study, these coordinative changes are specific to the training groups and may be a forerunner to improvements in vertical jumping.

PMID: 17614013 [PubMed - indexed for MEDLINE]

 

14: J Neurol Phys Ther. 2007 Mar;31(1):12-9.

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Weight-bearing exercise accuracy influences muscle activation strategies of the knee.

Madhavan S, Shields RK.

Graduate Program in Physical Therapy and Rehabilitation Science, The University of Iowa, Iowa City, IA, USA.

PURPOSE: Dynamic stability of the knee joint is a research topicof increasing focus after ACL injury, stroke, and incomplete spinal cord injury. Since rehabilitation programs use functional weightbearing tasks to improve neuromuscular control of the knee, it is important to understand the adaptability of muscle control strategies during weight-bearing exercise. The purpose of this study was to compare muscle activation patterns during a single leg squat (SLS) exercise performed before and after feedback-controlled training. METHODS: This was a cross-sectional comparative study. Fifteen young, healthy individuals performed the SLS exercise while tracking a sinusoidal target with flexion and extension of the knee. The SLS instrument provided bidirectional resistance that was normalized to body weight. Six trials of 10 repetitions of the SLSs were performed to quantify improved performance (learning). Electromyographic activity from five muscles that cross the knee was analyzed. Accuracy of performance was measured by calculating the error between the target and actual knee displacement. RESULTS: Reduction in error measurements verified that individuals increased the accuracy of performance in each trial and retained this improvement across trials (p < 0.05). Modulation in muscle activity as a result of learning was reflected mainly in the biceps femoris, rectus femoris, and vastus lateralis muscles. CONCLUSION: Increased accuracy with the SLS exercise was accompanied by a decrease in coactivation of selected musculature around the knee. This study presents a novel approach to quantify the effect of performance on muscle synergistic activation patterns during weight-bearing exercise. Controlled strengthening, as defined in this study, emphasizes accuracy of performance in conjunction with principles of strength training and has implications to knee control.

Publication Types:

• Controlled Clinical Trial

PMID: 17419885 [PubMed - indexed for MEDLINE]

 

15: J Strength Cond Res. 2007 Feb;21(1):123-30.

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Energy expenditure during bench press and squat exercises.

Robergs RA, Gordon T, Reynolds J, Walker TB.

Exercise Physiology Laboratories, University of New Mexico, Albuquerque 87131, USA. rrobergs@unm.edu

Despite the popularity of resistance training (RT), an accurate method for quantifying its metabolic cost has yet to be developed. We applied indirect calorimetry during bench press (BP) and parallel squat (PS) exercises for 5 consecutive minutes at several steady state intensities for 23 (BP) and 20 (PS) previously trained men. Tests were conducted in random order of intensity and separated by 5 minutes. Resultant steady state VO2 data, along with the independent variables load and distance lifted, were used in multiple regression to predict the energy cost of RT at higher loads. The prediction equation for BP was Y' = 0.132 + (0.031)(X1) + (0.01)(X2), R2 = 0.728 and S(xy) = 0.16; PS can be predicted by Y' = -1.424 + (0.022)(X1) + (0.035)(X2), R2 = 0.656 and S(xy) = 0.314; where Y' is VO2 X1 is the load measured in kg and X2 is the distance in cm. Based on a respiratory exchange ratio (RER) of 1.0 and a caloric equivalent of 5.05 kcal x L(-1), VO2 was converted to caloric expenditure (kcal x min(-1)). Using those equations to predict caloric cost, our resultant values were significantly larger than caloric costs of RT reported in previous investigations. Despite a potential limitation of our equations to maintain accuracy during very high-intensity RT, we propose that they currently represent the most accurate method for predicting the caloric cost of bench press and parallel squat.

PMID: 17313290 [PubMed - indexed for MEDLINE]

 

16: Am J Sports Med. 2007 Jun;35(6):927-32. Epub 2007 Feb 16.

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Three-dimensional motion analysis of the lumbar spine during "free squat" weight lift training.

Walsh JC, Quinlan JF, Stapleton R, FitzPatrick DP, McCormack D.

Cappagh National Orthopaedic Hospital, Finglas, Dublin, Republic of Ireland. james.walsh@ireland.com

BACKGROUND: Heavy weight lifting using a squat bar is a commonly used athletic training exercise. Previous in vivo motion studies have concentrated on lifting of everyday objects and not on the vastly increased loads that athletes subject themselves to when performing this exercise. HYPOTHESIS: Athletes significantly alter their lumbar spinal motion when performing squat lifting at heavy weights. STUDY DESIGN: Controlled laboratory study. METHODS: Forty-eight athletes (28 men, 20 women) performed 6 lifts at 40% maximum, 4 lifts at 60% maximum, and 2 lifts at 80% maximum. The Zebris 3D motion analysis system was used to measure lumbar spine motion. Exercise was performed as a "free" squat and repeated with a weight lifting support belt. Data obtained were analyzed using SAS. RESULTS: A significant decrease (P < .05) was seen in flexion in all groups studied when lifting at 40% maximum compared with lifting at 60% and 80% of maximum lift. Flexion from calibrated 0 point ranged from 24.7 degrees (40% group) to 6.8 degrees (80% group). A significant increase (P < .05) was seen in extension when lifting at 40% maximum was compared with lifting at 60% and 80% maximum lift. Extension from calibrated 0 point ranged from -1.5 degrees (40% group) to -20.3 degrees (80% group). No statistically significant difference was found between motion seen when exercise was performed as a free squat or when lifting using a support belt in any of the groups studied. CONCLUSION: Weight lifting using a squat bar causes athletes to significantly hyperextend their lumbar spines at heavier weights. The use of a weight lifting support belt does not significantly alter spinal motion during lifting.

PMID: 17307893 [PubMed - indexed for MEDLINE]

 

17: Br J Sports Med. 2007 Apr;41(4):264-8; discussion 268. Epub 2007 Jan 15.

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Biomechanical analysis of the single-leg decline squat.

Zwerver J, Bredeweg SW, Hof AL.

Center for Sports Medicine, University Center for Sport, Exercise and Health, University Medical Center Groningen, University of Groningen, The Netherlands. j.zwerver@sport.umcg.nl

BACKGROUND: The single-leg squat on a 25 degrees decline board has been described as a clinical assessment tool and as a rehabilitation exercise for patients with patellar tendinopathy. Several assumptions have been made about its working mechanism on patellar load and patellofemoral forces, but these are not substantiated by biomechanical evaluations. AIM: To investigate knee moment and patellofemoral contact force as a function of decline angle in the single-leg squat. METHODS: Five subjects performed single-leg eccentric squats at decline angles of 0 degrees, 5 degrees, 10 degrees, 15 degrees, 20 degrees and 25 degrees (with/without a backpack of 10 kg), and 30 degrees on a board that was placed over a forceplate. Kinematic and forceplate data were recorded by the Optotrak system. Joint moments of ankle, knee and hip were calculated by two-dimensional inverse dynamics. RESULTS: Knee moment increased by 40% at decline angles of 15 degrees and higher, whereas hip and ankle moment decreased. Maximum knee and ankle angles increased with steeper decline. With a 10 kg backpack at 25 degrees decline, the knee moment was 23% higher than unloaded. Both patellar tendon and patellofemoral forces increased with higher decline angles, but beyond 60 degrees, the patellofemoral force rose steeper than the tendon force. CONCLUSIONS: All single-leg squats at decline angles >15 degrees result in 40% increase in maximum patellar tendon force. In knee flexions >60 degrees, patellofemoral forces increase more than patellar tendon forces. Higher tendon load can be achieved by the use of a backpack with extra weight.

PMID: 17224441 [PubMed - indexed for MEDLINE]

 

18: J Strength Cond Res. 2006 Nov;20(4):915-8.

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Isometric squat force output and muscle activity in stable and unstable conditions.

McBride JM, Cormie P, Deane R.

Neuromuscular Laboratory, Department of Health, Leisure and Exercise Science, Applachian State University, Boone, NC 28607, USA. mcbridejm@appstate.edu

The purpose of this study was to assess the effect of stable vs. unstable conditions on force output and muscle activity during an isometric squat. Nine men involved in recreational resistance training participated in the investigation by completing a single testing session. Within this session subjects performed isometric squats either while standing directly on the force plate (stable condition, S) or while standing on inflatable balls placed on top of the force plate (unstable condition, U). Electromyography (EMG) was recorded during both conditions from the vastus lateralis (VL), vastus medialis (VM), biceps femoris (BF), and medial gastrocnemius (G) muscles. Results indicated peak force (PF) and rate of force development (RFD) were significantly lower, 45.6% and 40.5% respectively, in the U vs. S condition (p < or = 0.05). Average integrated EMG values for the VL and VM were significantly higher in the S vs. U condition. VL and VM muscle activity was 37.3% and 34.4% less in U in comparison to S. No significant differences were observed in muscle activity of the BF or G between U and S. The primary finding in this investigation is that isometric squatting in an unstable condition significantly reduces peak force, rate of force development, and agonist muscle activity with no change in antagonist or synergist muscle activity. In terms of providing a stimulus for strength gain no discernable benefit of performing a resistance exercise in an unstable condition was observed in the current study.

PMID: 17194253 [PubMed - indexed for MEDLINE]

 

19: J Sports Sci. 2007 Jan 15;25(2):193-200.

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The influence of squat depth on maximal vertical jump performance.

Domire ZJ, Challis JH.

University of Wyoming, Laramie, WY 82071, USA. zdomire@uwyo.edu

An increase in the period over which a muscle generates force can lead to the generation of greater force and, therefore, for example in jumping, to greater jump height. The aim of this study was to examine the effect of squat depth on maximum vertical jump performance. We hypothesized that jump height would increase with increasing depth of squat due to the greater time available for the generation of muscular force. Ten participants performed jumps from preferred and deep squat positions. A computer model simulated jumps from the different starting postures. The participants showed no difference in jump height in jumps from deep and preferred positions. Simulated jumps produced similar kinematics to the participants' jumps. The optimal squat depth for the simulated jumps was the lowest position the model was able to jump from. Because jumping from a deep squat is rarely practised, it is unlikely that these jumps were optimally coordinated by the participants. Differences in experimental vertical ground reaction force patterns also suggest that jumps from a deep squat are not optimally coordinated. These results suggest there is the potential for athletes to increase jump performance by exploiting a greater range of motion.

Publication Types:

• Research Support, Non-U.S. Gov't

PMID: 17127594 [PubMed - indexed for MEDLINE]

 

20: Eur Spine J. 2007 May;16(5):687-99. Epub 2006 Nov 14.

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Analysis of squat and stoop dynamic liftings: muscle forces and internal spinal loads.

Bazrgari B, Shirazi-Adl A, Arjmand N.

Department of Mechanical Engineering, Ecole Polytechnique, Montreal, QC, Canada.

Despite the well-recognized role of lifting in back injuries, the relative biomechanical merits of squat versus stoop lifting remain controversial. In vivo kinematics measurements and model studies are combined to estimate trunk muscle forces and internal spinal loads under dynamic squat and stoop lifts with and without load in hands. Measurements were performed on healthy subjects to collect segmental rotations during lifts needed as input data in subsequent model studies. The model accounted for nonlinear properties of the ligamentous spine, wrapping of thoracic extensor muscles to take curved paths in flexion and trunk dynamic characteristics (inertia and damping) while subject to measured kinematics and gravity/external loads. A dynamic kinematics-driven approach was employed accounting for the spinal synergy by simultaneous consideration of passive structures and muscle forces under given posture and loads. Results satisfied kinematics and dynamic equilibrium conditions at all levels and directions. Net moments, muscle forces at different levels, passive (muscle or ligamentous) forces and internal compression/shear forces were larger in stoop lifts than in squat ones. These were due to significantly larger thorax, lumbar and pelvis rotations in stoop lifts. For the relatively slow lifting tasks performed in this study with the lowering and lifting phases each lasting approximately 2 s, the effect of inertia and damping was not, in general, important. Moreover, posterior shift in the position of the external load in stoop lift reaching the same lever arm with respect to the S1 as that in squat lift did not influence the conclusion of this study on the merits of squat lifts over stoop ones. Results, for the tasks considered, advocate squat lifting over stoop lifting as the technique of choice in reducing net moments, muscle forces and internal spinal loads (i.e., moment, compression and shear force).

PMID: 17103232 [PubMed - indexed for MEDLINE]

PMCID: PMC2213554

 

21: J Appl Physiol. 2007 Jan;102(1):94-102. Epub 2006 Sep 7.

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Anticipatory responses of catecholamines on muscle force production.

French DN, Kraemer WJ, Volek JS, Spiering BA, Judelson DA, Hoffman JR, Maresh CM.

Human Performance Laboratory, Department of Kinesiology, Unit 1110, University of Connecticut, Storrs, CT 06269-1110, USA.

Few data exist on the temporal relationship between catecholamines and muscle force production in vivo. The purpose of this study was to examine the influence of preexercise arousal on sympathoadrenal neurohormones on muscular force expression during resistance exercise. Ten resistance-trained men completed two experimental conditions separated by 7 days: 1) acute heavy resistance exercise protocol (AHREP; 6 x 10 repetitions parallel squats, 80% 1 repetition maximum) and 2) control (Cont; rest). Peak force (F(peak)) was recorded during a maximal isometric squat preceding each set and mean force (F(mean)) was measured during each set. Serial venous blood samples were collected before the AHREP and immediately preceding each set. Blood collection times were matched during Cont. Preexercise epinephrine (Epi), norepinephrine (NE), and dopamine (DA) increased (P <or= 0.05) above Cont by 270, 255, and 164%, respectively. During exercise, Epi, NE, and DA continued to increase by 512, 271, and 38%, respectively, above preexercise values. F(peak) and F(mean) decreased by approximately 20-25% over the course of the AHREP. Post hoc data analysis revealed that five subjects (F(maintainers)) showed no decline (P >or= 0.05) in muscular performance (F(peak), F(mean)) during AHREP and that five subjects (F(reducers)) had significant reductions in F(peak) and F(mean). Integrated area under the curve for Epi, NE, and F(peak) were greater (P < 0.02) for F(maintainers) than F(reducers). In conclusion, an anticipatory rise in catecholamines existed, which may be essential for optimal force production at the onset of exercise.

Publication Types:

• Randomized Controlled Trial

PMID: 16959907 [PubMed - indexed for MEDLINE]

 

22: J Strength Cond Res. 2006 Aug;20(3):658-64.

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Peak power, ground reaction forces, and velocity during the squat exercise performed at different loads.

Zink AJ, Perry AC, Robertson BL, Roach KE, Signorile JF.

Department of Exercise and Sport Sciences, University of Miami, Coral Gables, FL 33124, USA. zink@gonzaga.edu

This study examined the changes in peak power, ground reaction force and velocity with different loads during the performance of the parallel squat movement. Twelve experienced male lifters (26.83 +/- 4.67 years of age) performed the standard parallel squat, using loads equal to 20, 30, 40, 50, 60, 70, 80, and 90% of 1 repetition maximum (1RM). Each subject performed all parallel squats with as much explosiveness as possible using his own technique. Peak power (PP), peak ground reaction force (PGRF), peak barbell velocity (PV), force at the time of PP (FPP), and velocity at the time of PP (VPP) were determined from force, velocity, and power curves calculated using barbell velocity and ground reaction force data. No significant differences were detected among loads for PP; however, the greatest PP values were associated with loads of 40 and 50% of 1RM. Higher loads produced greater PGRF and FPP values than lower loads (p < 0.05) in all cases except between loads equal to 60-50, 50-40, and 40-30% of 1RM for PGRF, and between loads equal to 70-60 and 60-50% of 1RM for FPP. Higher loads produced lower PV and VPP values than lower loads (p < 0.05) in all cases except between the 20-30, 70-80, and 80-90% of 1RM conditions. These results may be helpful in determining loads when prescribing need-specific training protocols targeting different areas of the load-velocity continuum.

PMID: 16937981 [PubMed - indexed for MEDLINE]

 

23: J Strength Cond Res. 2006 Aug;20(3):709-15.

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Analysis of biomechanical quantities during a squat jump: evaluation of a performance index.

Innocenti B, Facchielli D, Torti S, Verza A.

Dipartimento di Meccanica e Tecnologie Industriali, Università degli Studi di Firenze, Firenze, Italy. bernardo.innocenti@unifi.it

In this study, a procedure for evaluating the performance of an athlete in a squat jump has been developed. The athletes were divided into 2 categories according to their level of merit: elite athletes and non-elite athletes. In some of the subjects, the vertical component of acceleration during the squat jump was acquired with a uniaxial accelerometer. The acceleration-time curves obtained for each category of athletes were analyzed. Some analysis parameters suitable for establishing an athletic training level index were determined. A threshold value for this index that can be used to check gesture learning was also established, allowing the index to be used as a parameter for defining sport performance in a squat jump; thus it can also be used, during the training of an athlete, as the performance index to which reference should be made.

Publication Types:

• Research Support, Non-U.S. Gov't

PMID: 16937987 [PubMed - indexed for MEDLINE]

 

24: Ind Health. 2006 Jul;44(3):493-502.

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Effects of a new industrial lifting belt on back muscular activity, hand force, and body stability during symmetric lifting.

Chen HJ, Lin CJ, Huang CL.

Department of Industrial Engineering, Chung Yuan Christian University, Chung Li 32023, Taiwan.

This work investigated how wearing a new design of back belt affects erector spinae activity, hand force, and body stability. The belt was first tested with static holding tasks and found to significantly decrease the back muscle activity. Actual lifting tasks were further carried out to test the effect of the belt. Ten male subjects performed a symmetric lifting task of low-lying loads (11 and 16 kg) at natural toting velocity, using either a squat or stoop lifting posture, both with and without a belt. The study measured various independent variables using electromyography (EMG), load cells, and motion capture device. The results demonstrated that the belt reduced the load on the erector spinae, as well as the triceps brachii and biceps brachii. The overall mean values of the peak (hand) force did not appear significantly affected while wearing the belt, but the force peaks appeared postponed. The belt did not alter body stability while lifting. From the present findings, the belt effectively changed the force distribution during lifting, at least reducing the muscle load on the back. The belt may be a potentially useful device for symmetric industrial lifting tasks.

Publication Types:

• Research Support, Non-U.S. Gov't

PMID: 16922195 [PubMed - indexed for MEDLINE]

 

25: Med Sci Sports Exerc. 2006 Aug;38(8):1436-42.

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Oxidative stress response in trained men following repeated squats or sprints.

Bloomer RJ, Falvo MJ, Fry AC, Schilling BK, Smith WA, Moore CA.

Department of Health and Sport Sciences, The University of Memphis, Memphis, TN 38152, USA. rbloomer@memphis.edu

PURPOSE: The purpose of this investigation was to measure the oxidative stress response to similarly matched work bouts of squat and sprint exercise. METHODS: Twelve anaerobically trained men performed six 10-s sprints and, on a separate occasion, repeated barbell squats to approximately equal the amount of work performed during the sprints. Blood lactate, heart rate, and perceived exertion was measured before and following each exercise bout. Muscle soreness, muscle force, and creatine kinase activity was determined preexercise and through 48 h of recovery. Desmin cytoskeletal protein was determined via muscle biopsy of the vastus lateralis before and at 24 h following each exercise. Plasma protein carbonyls (PC) and malondialdehyde (MDA) were measured as biomarkers of oxidative stress. RESULTS: Heart rate and perceived exertion was not different between exercise sessions (P > 0.05), although lactate was higher following sprinting compared with squatting (P = 0.002). Muscle soreness was greater for squatting than sprinting (P = 0.003) and reached a peak immediately postexercise for both sessions (P = 0.0003). Muscle force was unaffected by either exercise session (P > 0.05), and creatine kinase activity was elevated to a similar extent following both sessions. Desmin-negative fibers were virtually nonexistent after either exercise bout, indicating no loss of this cytoskeletal protein. Neither PC nor MDA was affected by the exercise (P > 0.05). CONCLUSION: These results suggest that in anaerobically trained men, the oxidative stress and muscle injury response to similarly matched anaerobic exercise bouts is minimal, and not different between exercise modes. Furthermore, when compared with previous literature on untrained subjects, the response is significantly attenuated, possibly because of adaptations occurring as a result of chronic, strenuous anaerobic training.

PMID: 16888457 [PubMed - indexed for MEDLINE]

 

26: J Strength Cond Res. 2006 May;20(2):412-21.

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Adjusting powerlifting performances for differences in body mass.

Cleather DJ.

English Institute of Sport, St. Mary's College, Twickenham, UK. Daniel.Cleather@eis2win.co.uk

It has been established that, in the sports of Olympic weightlifting (OL) and powerlifting (PL), the relationship between lifting performance and body mass is not linear. This relationship has been frequently studied in OL, but the literature on PL is less extensive. In this study, PL performance and body mass, for both men and women, was examined by using data from the International Powerlifting Federation World Championships during 1995-2004. Nonlinear regression was used to apply 7 models (including allometric, polynomial, and power models) to the data. The results of this study indicate that the relationship between PL performance and body mass can be best modeled by the equation y = a - bx(-c), where y is the weight lifted (in kg) in the squat, bench press, or deadlift, x is the body mass of the lifter (in kg), and a, b, and c are constants. The constants a, b, and c are determined by the type of lift (squat, bench press, or deadlift) and the gender of the lifter and were obtained from the regression analysis. Inspection of the plots of raw residuals (actual performance minus predicted performance) vs. body mass revealed no body mass bias to this formula in contrast to research into other handicapping formulas. This study supports previous research that found a bias toward lifters in the intermediate weight categories in allometric fits to PL data.

PMID: 16686573 [PubMed - indexed for MEDLINE]

 

27: J Strength Cond Res. 2006 May;20(2):400-3.

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The effect of rest interval length on the sustainability of squat and bench press repetitions.

Willardson JM, Burkett LN.

Physical Education Department, Eastern Illinois University, Charleston, Illinois 61920, USA. cfjmw@eiu.edu

The purpose of this study was to compare the effect of 3 different rest intervals on the sustainability of squat and bench press repetitions over 5 consecutive sets performed with a 15 repetition maximum (RM)-load. Fifteen college-age men with previous resistance training experience were tested weekly over a period of 3 weeks. During each testing session, 5 consecutive sets of the squat and the bench press were performed with a 30-second, 1-minute, or 2-minute rest interval between sets. For each exercise, significant declines in repetitions occurred between the first and the fifth sets (p = 0.000). For the squat, a significant difference in the ability to sustain repetitions occurred between the 30-second and 2-minute rest condition (p = 0.003). However, differences were not significant between the 30-second and 1-minute rest conditions (p = 0.986) and between the 1-minute and 2-minute rest conditions (p = 0.042). For the bench press, significant differences in the ability to sustain repetitions occurred between the 30-second and 2-minute rest conditions (p = 0.000) and between the 1-minute and 2-minute rest conditions (p = 0.000). However, differences were not significant between the 30-second and 1-minute rest conditions (p = 0.019). For each exercise, the number of repetitions completed on the first set was not sustained over subsequent sets, irrespective of the rest condition. These results suggest that when short rest intervals are used to develop muscular endurance, the intensity should be lowered over subsequent sets to sustain repetitions within the range conducive to this training goal.

Publication Types:

• Comparative Study

PMID: 16686571 [PubMed - indexed for MEDLINE]

 

28: J Strength Cond Res. 2006 May;20(2):268-72.

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Effects of elastic bands on force and power characteristics during the back squat exercise.

Wallace BJ, Winchester JB, McGuigan MR.

Musculoskeletal Research Center, Department of Exercise and Sport Science, University of Wisconsin-La Crosse, La Crosse, Wisconsin 54601, USA.

Athletes commonly use elastic bands as a training method to increase strength and performance. The purpose of this study was to investigate the effect of elastic bands on peak force (PF), peak power (PP), and peak rate of force development (RFD) during the back-squat exercise (BSE). Ten recreationally resistance-trained subjects (4 women, 6 men, mean age 21.3 +/- 1.5 years) were tested for their 1 repetition maximum (1RM) in the BSE (mean 117.6 +/- 48.2 kg) on a Smith machine. Testing was performed on 2 separate days, with 2 sets of 3 repetitions being performed for each condition. Testing was conducted at 60% and 85% of 1RM with and without using elastic bands. In addition, 2 elastic band loading conditions were tested (B1 and B2) at each of the 2 resistances. No bands (NB) represents where all of the resistance was acquired from free-weights. B1 represents where approximately 80% of the resistance was provided by free-weights, and approximately 20% was provided by bands. B2 represents where approximately 65% of the resistance was provided by free-weights, and approximately 35% was provided from bands. The subjects completed the BSE under each condition, whereas PF, PP, and RFD was recorded using a force platform. There was a significant (p < 0.05) increase in PF between NB-85 and B2-85 of 16%. Between B1-85 and B2-85, PF was increased significantly by 5% (p < 0.05). There was a significant (p < 0.05) increase in PP between NB-85 and B2-85 of 24%. No significant differences were observed in RFD during the 85% conditions or for any of the measured variables during the 60% conditions (p < 0.05). The results suggest that the use of elastic bands in conjunction with free weights can significantly increase PF and PP during the BSE over free-weight resistance alone under certain loading conditions. The greatest differences are observed during the higher loading conditions, with the B1-85 condition appearing to be optimal for athletic performance of the ones we tested. The strength training professional could use variable resistance training (VRT) to increase PF and PP more than the traditional BSE can. VRT could also be used to train these 2 performance characteristics together, which might be especially useful in season, when weight-room training volume can sometimes be limited.

PMID: 16686552 [PubMed - indexed for MEDLINE]

 

29: Clin Biomech (Bristol, Avon). 2006 Aug;21(7):748-54. Epub 2006 May 3.

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Decline eccentric squats increases patellar tendon loading compared to standard eccentric squats.

Kongsgaard M, Aagaard P, Roikjaer S, Olsen D, Jensen M, Langberg H, Magnusson SP.

Institute of Sports Medicine, Bispebjerg Hospital, Department 8. Bispebjerg bakke 23, 2400 Copenhagen, Denmark. mk11@bbh.hosp.dk

BACKGROUND: Recent studies have shown excellent clinical results using eccentric squat training on a 25 degrees decline board to treat patellar tendinopathy. It remains unknown why therapeutic management of patellar tendinopathy using decline eccentric squats offer superior clinical efficacy compared to standard horizontal eccentric squats. This study aimed to compare electromyography activity, patellar tendon strain and joint angle kinematics during standard and decline eccentric squats. METHODS: Thirteen subjects performed unilateral eccentric squats on flat-and a 25 degrees decline surface. During the squats, electromyography activity was obtained in eight representative muscles. Also, ankle, knee and hip joint goniometry was obtained. Additionally, patellar tendon strain was measured in vivo using ultrasonography as subjects maintained a unilateral isometric 90 degrees knee angle squat position on either flat or 25 degrees decline surface. FINDINGS: Patellar tendon strain was significantly greater (P<0.05) during the squat position on the decline surface compared to the standard surface. The stop angles of the ankle and hip joints were significantly smaller during the decline compared to the standard squats (P<0.001, P<0.05). Normalized mean electromyography amplitudes of the knee extensor muscles were significantly greater during the decline compared to the standard squats (P<0.05). Hamstring and calf muscle mean electromyography did not differ, respectively, between standard and decline squats. INTERPRETATION: The use of a 25 degrees decline board increases the load and the strain of the patellar tendon during unilateral eccentric squats. This finding likely explains previous reports of superior clinical efficacy of decline eccentric squats in the rehabilitative management of patellar tendinopathy.

Publication Types:

• Controlled Clinical Trial

PMID: 16675081 [PubMed - indexed for MEDLINE]

 

30: Phys Ther. 2006 May;86(5):683-97.

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Neuromuscular activation in conventional therapeutic exercises and heavy resistance exercises: implications for rehabilitation.

Andersen LL, Magnusson SP, Nielsen M, Haleem J, Poulsen K, Aagaard P.

National Institute of Occupational Health, Lersø Parkalle 105, DK 2100 Copenhagen Ø, Denmark.

BACKGROUND AND PURPOSE: Central activation failure and muscular atrophy are common after knee joint injury. Thus, exercises that aim to stimulate muscular hypertrophy and increase neural drive to the muscle fibers should be used during rehabilitation. This study examined the level of knee joint neuromuscular activation during 4 conventional therapeutic exercises (quadriceps femoris muscle setting, manual lateralization of the patella, rhythmic stabilization, and the pelvic bridging exercise) and 4 heavy resistance exercises (free-weight squat with a barbell, horizontal seated leg press, isolated knee extension with a cam mechanism, and isolated hamstring muscle curl) in young, untrained men who were healthy. SUBJECTS: Thirteen male subjects (mean age=25.3 years, SD=3.0) with no previous history of knee injury participated in the study. METHODS: Neuromuscular activation during the exercises was defined as the root-mean-square (RMS) electromyographic (EMG) signal normalized to the peak RMS EMG signal of a maximal isometric muscle contraction. RESULTS: Low levels of neuromuscular activation were found during all conventional exercises (<35%). A limitation may be that only a few of many different conventional exercises were investigated. The highest level of neuromuscular activation (67%-79%) was observed during the open kinetic chain resistance exercises (isolated knee extension and hamstring muscle curl). None of the conventional exercises or heavy resistance exercises were found to preferentially activate the vastus medialis muscle over the vastus lateralis muscle. DISCUSSION AND CONCLUSION: The results indicate that heavy resistance exercises should be included in rehabilitation programs to induce sufficient levels of neuromuscular activation to stimulate muscle growth and strength.

Publication Types:

• Comparative Study

PMID: 16649892 [PubMed - indexed for MEDLINE]

 

31: J Athl Train. 1999 Oct;34(4):353-357.

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An Electromyographic Comparison of 4 Closed Chain Exercises.

Hopkins JT, Ingersoll CD, Sandrey MA, Bleggi SD.

Indiana State University, Terre Haute, IN.

OBJECTIVE: Closed chain exercises are used in the clinical setting to safely strengthen the muscles about the knee. We compared the EMG activity of 3 muscles (vastus lateralis, vastus medialis, and biceps femoris) during 4 closed chain exercises (unilateral one-quarter squat, lateral step-up, FlexCord front pull, and FlexCord back pull) to determine which exercise produced the most muscle activity. DESIGN AND SETTING: We used a 4 x 3 x 2 factorial design with repeated measures on exercise, muscle, and movement (knee flexion and extension). Muscle and movement were the control variables for post hoc comparisons. Data were collected in a sports injury research laboratory. SUBJECTS: Thirty-eight healthy, active female college students aged 21.97 +/- 2.8 years, with height 166.9 +/- 6.3 cm and weight 61.9 +/- 8.5 kg. Subjects had no history of lower extremity pathology that resulted in surgery and no lower extremity pathology within the last year. MEASUREMENTS: We placed surface electrodes on the vastus lateralis, vastus medialis, and biceps femoris muscles. Synchronized with a metronome, subjects performed 3 repetitions of 4 exercises between 5 degrees and 30 degrees of knee flexion. Electromyographic measurements were taken from the middle third of the flexion and extension phase of each repetition. RESULTS: The FlexCord front pull and back pull produced higher levels of biceps femoris activity than the quarter squat and step-up. The FlexCord front pull also produced a higher level of vastus medialis activity during knee extension than the quarter squat, lateral step-up, or FlexCord back pull. CONCLUSIONS: The high levels of biceps femoris activity during the FlexCord exercises indicate that a greater cocontraction exists. With a greater cocontraction, the FlexCord exercises could be safely used during ACL rehabilitation. The high levels of vastus medialis activity during the FlexCord front pull suggest that it may be a beneficial exercise for patellofemoral rehabilitation.

PMID: 16558588 [PubMed - as supplied by publisher]

PMCID: PMC1323346

 

32: J Strength Cond Res. 2006 Feb;20(1):145-50.

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The effect of the direction of gaze on the kinematics of the squat exercise.

Donnelly DV, Berg WP, Fiske DM.

Department of Intercollegiate Athletics, Miami University, Oxford, Ohio 45056, USA.

The purpose of this study was to determine whether the direction of gaze influences the kinematics of the squat exercise. Ten men experienced in the squat exercise performed a total of 30 repetitions of the squat in the form of 2 sets of 5 repetitions under 3 different conditions. Conditions varied with respect to the direction of the subjects' gaze as they performed the exercise. Condition D entailed gazing downward at the intersection of the facing wall and the floor throughout the exercise. Condition S required subjects to gaze straight ahead at their own reflection (eyes) in the mirror on the wall directly in front of them. Condition U involved gazing upward at the intersection of the facing wall and the ceiling throughout the exercise. Dependent variables included the linear displacement of the bar and hip, linear velocity of the bar, and the angular displacement/position and velocity of the head, trunk, hip, and knee. The mean data were subjected to a repeated measures analysis of variance, and, where appropriate, pairwise comparisons using Tukey's Studentized Range Test. The results revealed overall similarity in movement kinematics when performing the squat exercise using the 3 different gaze directions. In particular, the upward and straight gaze conditions were not differentiated by the analysis. Conversely, the downward gaze was shown to increase the extent of hip flexion (F[2, 9] = 4.82, p < .05), especially relative to the upward gaze, and possibly trunk flexion as well (F[2, 9] = 3.02, p = .07). In terms of the practical application, because excessive hip and trunk flexion in the squat are contraindicated, cautioning athletes against allowing the head or direction of gaze to drop below a neutral position appears to be warranted.

PMID: 16503674 [PubMed - indexed for MEDLINE]

 

33: J Strength Cond Res. 2006 Feb;20(1):141-4.

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Influence of exercise order in a resistance-training exercise session.

Spreuwenberg LP, Kraemer WJ, Spiering BA, Volek JS, Hatfield DL, Silvestre R, Vingren JL, Fragala MS, Häkkinen K, Newton RU, Maresh CM, Fleck SJ.

Department of Movement Sciences, University of Maastricht, Netherlands.

The order of resistance exercises within a training session may have a vital impact on the quality of the constituent exercises performed. However, very few studies have documented the specific influence of exercise order. Therefore, the purpose of this study was to examine the effect of exercise order on back squat performance in the context of a whole-body workout. Nine resistance-trained male subjects (age: 24 +/- 4 years, body mass: 81.5 +/- 15.3 kg, resistance-training experience: 7 +/- 4 years) performed the back squat exercise (4 sets at 85% of 1 repetition maximum) on 2 separate occasions in a balanced, crossover design. During one protocol, the squat exercise was performed first (protocol A); during the other protocol, it was performed after a whole-body resistance-exercise session (protocol B). Number of repetitions, average power, and rating of perceived exertion (RPE) were collected during each set of the squat exercise. All subjects performed significantly (p < 0.01) more repetitions during set 1 when they performed protocol A (8.0 +/- 1.9 repetitions) compared with protocol B (5.4 +/- 2.7 repetitions). The average power for each set was higher during protocol B compared with protocol A. There were no significant differences in RPE values between the 2 protocols. In conclusion, performing the barbell back squat first in an exercise session allowed the completion of more total repetitions. However, this study showed that performing the squat exercise after a whole-body workout session may result in greater power output if the squat is preceded by a power exercise (i.e., hang pull). This phenomenon may have been due to postactivation potentiation.

PMID: 16503673 [PubMed - indexed for MEDLINE]

 

34: Percept Mot Skills. 2005 Aug;101(1):195-202.

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Observation of action and autonomic nervous system responses.

Bolliet O, Collet C, Dittmar A.

Centre de Recherche et d'Innovation sur le Sport Université Claude Bernard Lyon 1, Villeurbanne Cedex, France.

Observing somebody performing an action has been shown to elicit neuronal activity in the premotor cortex. This paper investigated physiological effect of observing an effortful action at the peripheral level. As Autonomic Nervous System responses reflect central nervous system processes such as movement planning and programming, it was expected that observing an action would elicit a pattern of ANS responses matching those recorded during actual movement. 12 male subjects, ages 23 to 28 years (M = 25.5, SD = 1.9), were selected as they were experienced in weight lifting. They were asked to observe a squat movement followed by returning to the upright position under 3 different conditions: (i) observation of actual movement performed by somebody else, (ii) observation of a video of the subject himself (first-person video), and (iii) observation of a video of somebody else performing the same movement (third-person video). Moreover, each movement was observed when performed at 50% and 90% of each participant's personal best mark (% of the highest weight which could be lifted). Three ANS parameters were continuously recorded: skin resistance, temperature and heart rate. ANS responses varied as a function of movement intensity: autonomic responses recorded during movement observation at 90% were significantly higher and longer than those recorded during movement observation at 50%. Thus, autonomic responses were linked to the amount of observed effort. Conversely, no difference was found among the three conditions of observation. ANS responses from observation of actual movement were shown to resemble those recorded under the two conditions of video observation.

PMID: 16350624 [PubMed - indexed for MEDLINE]

 

35: J Sports Sci. 2005 Jul;23(7):687-92.

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Maximal strength and cortisol responses to psyching-up during the squat exercise.

McGuigan MR, Ghiagiarelli J, Tod D.

School of Biomedical and Sports Science, Edith Cowan University, Joondalup, WA, Australia. m.mcguigan@ecu.edu.au

We studied the effect of psyching-up on one-repetition maximum (1-RM) performance and salivary cortisol responses during the squat exercise. Ten men (age 21.6+/-1.4 years; mean+/-s) and ten women (age 22.4+/-2.8 years) with weight training experience of 4.5+/-2.0 years participated in this study. One-repetition maximum squats were performed on a Smith machine during each of two different intervention conditions that were counterbalanced and consisted of a free choice psych-up and a cognitive distraction. Saliva samples were obtained at the beginning of each test session and immediately after the final 1-RM attempt. No significant difference in 1-RM was identified between psyching-up (104+/-50 kg) and cognitive distraction (106+/-52 kg). Performing a 1-RM in the squat exercise significantly increased salivary cortisol concentrations during both conditions (P<0.05). There was no significant difference in salivary cortisol responses between conditions. These results suggest that psyching-up does not increase 1-RM performance during the squat exercise in strength-trained individuals.

Publication Types:

• Comparative Study

PMID: 16195018 [PubMed - indexed for MEDLINE]

 

36: Med Sci Sports Exerc. 2005 Jun;37(6):1037-43.

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Relationship of maximum strength to weightlifting performance.

Stone MH, Sands WA, Pierce KC, Carlock J, Cardinale M, Newton RU.

Coaching and Sports Science, United States Olympic Committee, Colorado Springs, CO 80909, USA. mike.stone@usoc.org

PURPOSE: The primary objective was to assess the relationship of maximum strength to weightlifting ability using established scaling methods. The secondary objective was to compare men and women weightlifters on strength and weightlifting ability. METHODS: Two correlational observations were carried out using Pearson's r. In the first observation (N = 65) the relationship of dynamic maximum strength (one-repetition maximum (1RM) squat) was compared with weightlifting ability; in the second observation (N = 16), isometric maximum strength (midthigh pull) was studied. Scaling methods for equating maximum strength and weightlifting results were used (load x (Ht), load x kg, load x lbm(-1), allometric, and Sinclair formula) to assess the association between measures of maximum strength and weightlifting performance. RESULTS: Using scaled values; correlations between maximum strength and weightlifting results were generally strong in both observations (e.g., using allometric scaling for the 1RM squat vs the 1RM snatch: r = 0.84, N = 65). Men were stronger than women (e.g., 1RM squat, N = 65: men = 188.1 +/- 48.6 kg; women = 126.7 +/- 28.3 kg); differences generally held when scaling was applied (e.g., 1RM squat scaled with the Sinclair formula: men = 224.7 +/- 36.5 kg; women = 144.2 +/- 25.4 kg). CONCLUSIONS: When collectively considering scaling methods, maximum strength is strongly related to weightlifting performance independent of body mass and height differences. Furthermore, men are stronger than women even when body mass and height are obviated by scaling methods.

PMID: 15947731 [PubMed - indexed for MEDLINE]

 

37: J Strength Cond Res. 2005 May;19(2):433-7.

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Short-term effects on lower-body functional power development: weightlifting vs. vertical jump training programs.

Tricoli V, Lamas L, Carnevale R, Ugrinowitsch C.

Department of Sport, School of Physical Education and Sport, University of Sao Paulo, Sao Paulo, SP, Brazil. vtricoli@usp.br

Among sport conditioning coaches, there is considerable discussion regarding the efficiency of training methods that improve lower-body power. Heavy resistance training combined with vertical jump (VJ) training is a well-established training method; however, there is a lack of information about its combination with Olympic weightlifting (WL) exercises. Therefore, the purpose of this study was to compare the short-term effects of heavy resistance training combined with either the VJ or WL program. Thirty-two young men were assigned to 3 groups: WL = 12, VJ = 12, and control = 8. These 32 men participated in an 8-week training study. The WL training program consisted of 3 x 6RM high pull, 4 x 4RM power clean, and 4 x 4RM clean and jerk. The VJ training program consisted of 6 x 4 double-leg hurdle hops, 4 x 4 alternated single-leg hurdle hops, 4 x 4 single-leg hurdle hops, and 4 x 4 40-cm drop jumps. Additionally, both groups performed 4 x 6RM half-squat exercises. Training volume was increased after 4 weeks. Pretesting and posttesting consisted of squat jump (SJ) and countermovement jump (CMJ) tests, 10- and 30-m sprint speeds, an agility test, a half-squat 1RM, and a clean-and-jerk 1RM (only for WL). The WL program significantly increased the 10-m sprint speed (p < 0.05). Both groups, WL and VJ, increased CMJ (p < 0.05), but groups using the WL program increased more than those using the VJ program. On the other hand, the group using the VJ program increased its 1RM half-squat strength more than the WL group (47.8 and 43.7%, respectively). Only the WL group improved in the SJ (9.5%). There were no significant changes in the control group. In conclusion, Olympic WL exercises seemed to produce broader performance improvements than VJ exercises in physically active subjects.

Publication Types:

• Clinical Trial
• Comparative Study
• Controlled Clinical Trial

PMID: 15903387 [PubMed - indexed for MEDLINE]

 

38: J Strength Cond Res. 2005 May;19(2):421-6.

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Effect of potentiation and stretching on maximal force, rate of force development, and range of motion.

Bazett-Jones DM, Winchester JB, McBride JM.

Musculoskeletal Research Center, Department of Exercise and Sport Science, University of Wisconsin-La Crosse, La Crosse, Wisconsin 54601, USA.

The purpose of this investigation was to compare the effects of stretching vs. potentiation on subsequent maximal force and rate of force development capabilities of subjects in an isometric squat. Ten male collegiate athletes participated as subjects in this study. Subjects were tested during 3 separate sessions that involved joint range of motion (ROM) measurements of the lower body and isometric squat trials on a force plate to determine peak force (PF) and rate of force development (RFD) values. One testing session was preceded by 10 minutes of quiet sitting (C), 1 by a 30-minute lower-body stretching protocol (S), and 1 by 3 sets of a leg press exercise using 90% of the subjects' previously determined 1 repetition maximum (P). Three repetitions were performed for each set of the leg press, with a 3-minute rest period between each set. PF during the isometric squat was not significantly different following any of the 3 conditions (C: 100.0 +/- 0.0%, S: 101.2 +/- 6.5%, P: 98.6 +/- 6.2%). However, RFD was significantly lower in P (87.5 +/- 12.8%) compared with both C (100.0 +/- 0.0%) and S (102.6 +/- 18.5%). Significant improvement in ROM occurred only following P. It appears the potentiation protocol used in the current investigation may actually have had fatiguing effects instead of potentiating effects, but it did result in significant increases in ROM.

Publication Types:

• Clinical Trial
• Controlled Clinical Trial

PMID: 15903385 [PubMed - indexed for MEDLINE]

 

39: Can J Appl Physiol. 2005 Feb;30(1):33-45.

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Trunk muscle activity increases with unstable squat movements.

Anderson K, Behm DG.

School of Human Kinetics and Recreation, Memorial University of Newfoundland, St. John's, Newfoundland, A1C 5S7.

The objective of this study was to determine differences in electromyographic (EMG) activity of the soleus (SOL), vastus lateralis (VL), biceps femoris (BF), abdominal stabilizers (AS), upper lumbar erector spinae (ULES), and lumbo-sacral erector spinae (LSES) muscles while performing squats of varied stability and resistance. Stability was altered by doing the squat movement on a Smith machine, a free squat, and while standing on two balance discs. Fourteen male subjects performed the movements. Activities of the SOL, AS, ULES, and LSES were highest during the unstable squat and lowest with the Smith machine protocol (p < 0.05). Increased EMG activity of these muscles may be attributed to their postural and stabilization role. Furthermore, EMG activity was higher during concentric contractions compared to eccentric contractions. Performing squats on unstable surfaces may permit a training adaptation of the trunk muscles responsible for supporting the spinal column (i.e., erector spinae) as well as the muscles most responsible for maintaining posture (i.e., SOL).

Publication Types:

• Comparative Study

PMID: 15855681 [PubMed - indexed for MEDLINE]

 

40: J Steroid Biochem Mol Biol. 2005 Jan;93(1):35-42. Epub 2005 Jan 25.

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Androgen receptor content following heavy resistance exercise in men.

Ratamess NA, Kraemer WJ, Volek JS, Maresh CM, Vanheest JL, Sharman MJ, Rubin MR, French DN, Vescovi JD, Silvestre R, Hatfield DL, Fleck SJ, Deschenes MR.

Human Performance Laboratory, Department of Kinesiology, Unit 1110, University of Connecticut, Storrs, CT 06269-1110, USA.

The purpose of the present investigation was to examine androgen receptor (AR) content in the vastus lateralis following two resistance exercise protocols of different volume. Nine resistance-trained men (age=24.3+/-4.4 years) performed the squat exercise for 1 (SS) and 6 sets (MS) of 10 repetitions in a random, counter-balanced order. Muscle biopsies were performed at baseline, and 1h following each protocol. Blood was collected prior to, immediately following (IP), and every 15 min after each protocol for 1h. No acute elevations in serum total testosterone were observed following SS, whereas significant 16-23% elevations were observed at IP, 15, and 30 min post-exercise following MS. No acute elevations in plasma cortisol were observed following SS, whereas significant 31-49% elevations were observed for MS at IP, 15, and 30 min post-exercise. Androgen receptor content did not change 1h following SS but significantly decreased by 46% following MS. These results demonstrated that a higher volume of resistance exercise resulted in down-regulation of AR content 1h post-exercise. This may have been due to greater protein catabolism associated with the higher level of stress following higher-volume resistance exercise.

Publication Types:

• Research Support, Non-U.S. Gov't

PMID: 15748830 [PubMed - indexed for MEDLINE]

 

41: J Orthop Res. 2005 Mar;23(2):345-50.

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Patellofemoral joint contact area increases with knee flexion and weight-bearing.

Besier TF, Draper CE, Gold GE, Beaupré GS, Delp SL.

VA Rehabilitation Research and Development Center, Palo Alto, CA, USA. besier@stanford.edu

Patellofemoral pain is a common and debilitating disorder. Elevated cartilage stress of the patellofemoral joint is hypothesized to play a role in the onset of pain. Estimating cartilage stress requires accurate measurements of contact area. The purpose of this study was to estimate patellofemoral joint contact areas in a group of healthy, pain-free subjects during upright, weight-bearing conditions. Sixteen subjects (8 female, 8 male) were scanned in a GE Signa SP open configuration MRI scanner, which allowed subjects to stand or squat while reclining 25 degrees from vertical with the knee positioned at 0 degrees , 30 degrees , or 60 degrees of flexion. A custom-built backrest enabled subjects to be scanned without motion artifact in both weight-bearing (0.45 body weight per leg) and reduced loading conditions ('unloaded' at 0.15 body weight) at each knee flexion posture. Male subjects displayed mean unloaded patellofemoral joint contact areas of 210, 414, and 520 mm(2) at 0 degrees , 30 degrees and 60 degrees of knee flexion, respectively. Female subjects' unloaded contact areas were similar at full extension (0 degrees ), but significantly smaller at 30 degrees and 60 degrees (p<0.01), with mean values of 269 and 396 mm(2), respectively. When normalized by patellar dimensions (heightxwidth), contact areas were not different between genders. Under weight-bearing conditions, contact areas increased by an average of 24% (p<0.05). This study highlights the differences in patellofemoral joint contact area between gender, knee flexion postures, and physiologic loading conditions.

Publication Types:

• Research Support, Non-U.S. Gov't
• Research Support, U.S. Gov't, Non-P.H.S.

PMID: 15734247 [PubMed - indexed for MEDLINE]

 

42: Metabolism. 2005 Feb;54(2):151-6.

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The effect of resistance training combined with timed ingestion of protein on muscle fiber size and muscle strength.

Andersen LL, Tufekovic G, Zebis MK, Crameri RM, Verlaan G, Kjaer M, Suetta C, Magnusson P, Aagaard P.

Sports Medicine Research, Unit/Team Denmark Test Center, Bispebjerg Hospital, DK-2400 Copenhagen, Denmark. LL_andersen@hotmail.com

Acute muscle protein metabolism is modulated not only by resistance exercise but also by amino acids. However, less is known about the long-term hypertrophic effect of protein supplementation in combination with resistance training. The present study was designed to compare the effect of 14 weeks of resistance training combined with timed ingestion of isoenergetic protein vs carbohydrate supplementation on muscle fiber hypertrophy and mechanical muscle performance. Supplementation was administered before and immediately after each training bout and, in addition, in the morning on nontraining days. Muscle biopsy specimens were obtained from the vastus lateralis muscle and analyzed for muscle fiber cross-sectional area. Squat jump and countermovement jump were performed on a force platform to determine vertical jump height. Peak torque during slow (30 degrees s-1) and fast (240 degrees s-1) concentric and eccentric contractions of the knee extensor muscle was measured in an isokinetic dynamometer. After 14 weeks of resistance training, the protein group showed hypertrophy of type I (18% +/- 5%; P < .01) and type II (26% +/- 5%; P < .01) muscle fibers, whereas no change above baseline occurred in the carbohydrate group. Squat jump height increased only in the protein group, whereas countermovement jump height and peak torque during slow isokinetic muscle contraction increased similarly in both groups. In conclusion, a minor advantage of protein supplementation over carbohydrate supplementation during resistance training on mechanical muscle function was found. However, the present results may have relevance for individuals who are particularly interested in gaining muscle size.

Publication Types:

• Clinical Trial
• Randomized Controlled Trial
• Research Support, Non-U.S. Gov't

PMID: 15690307 [PubMed - indexed for MEDLINE]

 

43: Exp Brain Res. 2005 Jun;163(3):344-51. Epub 2005 Jan 15.

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Observation, imagination and execution of an effortful movement: more evidence for a central explanation of motor imagery.

Mulder T, de Vries S, Zijlstra S.

Center for Human Movement Sciences, University of Groningen, P.O. Box 196, 9700 AD , Groningen, The Netherlands. t.mulder@ppsw.rug.nl

In this study subjects had to imagine, observe and perform a series of 25 squat movements while lifting two dumbbells of 12.5 kg each (one with each hand). This movement is effortful and requires substantial activation of peripheral systems. It was asked whether subjects when they imagined that they were performing the movements or when they observed a model performing the squat movements would show increased activity in EMG, heart rate and respiration compared with a control condition where they sat relaxed in a comfortable chair or a condition where they actually performed the squat movements. Two groups of subjects participated in the experiment: experienced squatters and novices. By employing these two groups we were able to study the differential effect of earlier experience with the target movement on peripheral activation. The results showed that with the exception of respiration no significant peripheral activation could be measured related to motor imagery. Although a clear distinction in experience existed between the experienced squatters versus the novices, no relevant imagery-related differences could be obtained between the two groups. The results are discussed in the light of a central explanation of motor imagery.

PMID: 15654585 [PubMed - indexed for MEDLINE]

 

44: Ergonomics. 2004 Oct 22;47(13):1365-85.

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Foot positioning instruction, initial vertical load position and lifting technique: effects on low back loading.

Kingma I, Bosch T, Bruins L, van Dieën JH.

Institute for Fundamental and Clinical Human Movement Sciences, Faculty of Human Movement Sciences, Vrije Universiteit, Van der Boechorststraat 9, 1081 BT Amsterdam, The Netherlands. i_kingma@fbw.vu.nl

This study investigated the effects of initial load height and foot placement instruction in four lifting techniques: free, stoop (bending the back), squat (bending the knees) and a modified squat technique (bending the knees and rotating them outward). A 2D dynamic linked segment model was combined with an EMG assisted trunk muscle model to quantify kinematics and low back loading in 10 subjects performing 19 different lifting movements, using 10.5 kg boxes without handles. When lifting from a 0.05 m height with the feet behind the box, squat lifting resulted in 19.9% (SD 8.7%) higher net moments (p < 0.001) and 17.0% (SD 13.2%) higher compression forces (p < 0.01) than stoop lifting. This effect was reduced to 12.8% (SD 10.7%) for moments and a non-significant 7.4% (SD 16.0%) for compression forces when lifting with the feet beside the box and it disappeared when lifting from 0.5 m height. Differences between squat and stoop lifts, as well as the interaction with lifting height, could to a large extent be explained by changes in the horizontal L5/S1 intervertebral joint position relative to the load, the upper body acceleration, and lumbar flexion. Rotating the knees outward during squat lifts resulted in moments and compression forces that were smaller than in squat lifting but larger than in stoop lifting. Shear forces were small ( < 300 N) at the L4/L5 joint and substantial (1100 - 1400 N) but unaffected by lifting technique at the L5/S1 joint. The present results show that the effects of lifting technique on low back loading depend on the task context.

Publication Types:

• Clinical Trial

PMID: 15513714 [PubMed - indexed for MEDLINE]

 

45: J Sci Med Sport. 2004 Jun;7(2):144-55.

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Training volume and strength and power development.

Cronin J, Crewther B.

Sport Performance Research Centre, Auckland University of Technology, New Zealand.

The purpose of this study was to determine if three training loads equated by volume differed in terms of the temporal, kinematic and kinetic characteristics of each set. Twelve experienced weightlifters (30.2+/-10.6 years old and 75.8+/-13.0 kg) performed three sets (6 x 30% 1RM, 3 x 60% 1RM and 2 x 90% 1RM) of ballistic squats on an instrumented supine squat machine. Repeated measures ANOVA and Tukey HSD post hoc comparisons were used to distinguish significant differences between the three training loads on a variety of temporal, kinematic and kinetic variables. Significantly (p< 0.05) greater total time under tension during the eccentric (41-53%) and concentric phases (27-31%) was observed for the 30% 1RM condition compared to the other two conditions. Similarly, the lighter loading intensity resulted in significantly greater total eccentric (9-19%) and concentric (14-24%) force output compared to the other two conditions. Greater total power output was associated with the 30% 1RM condition for both the eccentric (25-48%) and concentric (40-69%) phases. Greater total work (9-24%) was also associated with the 30% 1RM condition. The 60% 1RM condition produced significantly greater total work, force and power compared to the 90% 1RM condition. However, greater concentric impulse (29-42%) was associated with the 90% 1RM condition. It is suggested that strength and power research needs to adopt a set kinematic and kinetic analysis approach within the research designs so that a better understanding of the nature of the neuromuscular adaptations elicited by different loading parameters is achieved.

Publication Types:

• Clinical Trial
• Comparative Study

PMID: 15362310 [PubMed - indexed for MEDLINE]

 

46: J Biomech. 2004 Sep;37(9):1329-37.

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Effect of the "squat protective response" on impact velocity during backward falls.

Robinovitch SN, Brumer R, Maurer J.

Injury Prevention and Mobility Laboratory, School of Kinesiology, Simon Fraser University, 8888 University Drive, Vancouver, Burnaby, BC V5A 1S6, Canada. stever@sfu.ca

Risk for injury during a fall depends on the position and velocity of the body segments at the moment of impact. One technique for reducing impact velocity is to absorb energy in the lower extremity muscles during descent, as occurs during squatting or sitting. However, the protective value of this response may depend on the time during descent when the response is initiated. We tested this hypothesis by conducting backward falling experiments with young women (n = 23; aged 21-29 years), who fell onto a soft gymnasium mattress after being suddenly releasing from an inclined position. In trials where subjects were released from a 5 degrees lean, average impact velocities were reduced by 18% when squatting was utilized as opposed to inhibited. Furthermore, increases in the release angle caused an increase in average impact velocity of 8% between lean angles of 2 degrees and 5 degrees, and 7% between lean angles of 5 degrees and 12 degrees. This was due to declines in peak extensor torques and peak flexion rotations, and corresponding reductions in both joint work and potential energy at impact. These results suggest that squatting during descent reduces impact severity, but the effectiveness of the response depends on the stage during descent when it is initiated, diminishing in benefit as the fall progresses and the state of imbalance grows increasingly severe.

Publication Types:

• Clinical Trial
• Controlled Clinical Trial
• Research Support, Non-U.S. Gov't
• Research Support, U.S. Gov't, P.H.S.

PMID: 15275840 [PubMed - indexed for MEDLINE]