home - por que - blog - bodybuilding - educação física - treinamento de força - musculosos - imagem corporal - serviços e pessoas - imagens - quem sou eu

Bibliografia sobre Agachamento

Items 1 - 36 of 36
One page.
 
1: Eur Spine J. 2007 May;16(5):687-99. Epub 2006 Nov 14.
Related Articles, Links
Click here to read Click here to read
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

 
2: Phys Ther. 2000 Jun;80(6):570-7.
Related Articles, Links
Click here to read
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:


PMID: 10842410 [PubMed - indexed for MEDLINE]

 
3: Spine. 2001 Aug 15;26(16):1794-8.
Related Articles, Links
Click here to read
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:


PMID: 11493853 [PubMed - indexed for MEDLINE]

 
4: Phys Ther. 1987 Sep;67(9):1329-34.
Related Articles, Links

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:


PMID: 2957703 [PubMed - indexed for MEDLINE]

 
5: Ergonomics. 1998 Jun;41(6):790-7.
Related Articles, Links

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:


PMID: 9629064 [PubMed - indexed for MEDLINE]

 
6: Spine. 2007 Jul 1;32(15):1599-604.
Related Articles, Links
Click here to read
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]
 
7: Spine. 2005 Oct 15;30(20):2265-73.
Related Articles, Links
Click here to read
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:


PMID: 16227888 [PubMed - indexed for MEDLINE]

 
8: Eur J Appl Physiol. 2008 Feb;102(3):299-305. Epub 2007 Oct 13.
Related Articles, Links
Click here to read
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:


PMID: 17934755 [PubMed - indexed for MEDLINE]

 
9: Phys Ther. 1995 Feb;75(2):133-44.
Related Articles, Links
Click here to read
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:


PMID: 7846133 [PubMed - indexed for MEDLINE]

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

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:


PMID: 11411626 [PubMed - indexed for MEDLINE]

 
11: Spine. 1998 Oct 1;23(19):2104-9.
Related Articles, Links
Click here to read
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:


PMID: 9794055 [PubMed - indexed for MEDLINE]

 
12: Spine. 2002 Nov 15;27(22):2514-20.
Related Articles, Links
Click here to read
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:


PMID: 12435984 [PubMed - indexed for MEDLINE]

 
13: Clin Biomech (Bristol, Avon). 1995 Apr;10(3):122-127.
Related Articles, Links
Click here to read
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]
 
14: Spine. 1995 Jun 1;20(11):1271-8; discussion 1278.
Related Articles, Links

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]
 
15: Spine. 1995 Jan 1;20(1):68-73.
Related Articles, Links

Comment in:


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:


PMID: 7709282 [PubMed - indexed for MEDLINE]

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

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:


PMID: 14636099 [PubMed - indexed for MEDLINE]

 
17: Ergonomics. 1993 Dec;36(12):1489-93.
Related Articles, Links

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:


PMID: 8287855 [PubMed - indexed for MEDLINE]

 
18: Ergonomics. 2000 May;43(5):653-68.
Related Articles, Links

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:


PMID: 10877482 [PubMed - indexed for MEDLINE]

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

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:


PMID: 12580658 [PubMed - indexed for MEDLINE]

 
20: Arch Phys Med Rehabil. 2002 Jan;83(1):48-59.
Related Articles, Links
Click here to read
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:


PMID: 11782833 [PubMed - indexed for MEDLINE]

 
21: Clin Biomech (Bristol, Avon). 2000 Aug;15(7):469-77.
Related Articles, Links
Click here to read
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:


PMID: 10831806 [PubMed - indexed for MEDLINE]

 
22: Hum Factors. 1995 Dec;37(4):844-53.
Related Articles, Links

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:


PMID: 8851780 [PubMed - indexed for MEDLINE]

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

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]
 
24: Am J Occup Ther. 2000 Mar-Apr;54(2):166-75.
Related Articles, Links

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:


PMID: 10732178 [PubMed - indexed for MEDLINE]

 
25: J Sports Sci. 2005 Jul;23(7):687-92.
Related Articles, Links
Click here to read
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:


PMID: 16195018 [PubMed - indexed for MEDLINE]

 
26: Spine. 2002 Jun 1;27(11):1208-12.
Related Articles, Links
Click here to read
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:


PMID: 12045519 [PubMed - indexed for MEDLINE]