Search

Prolonged repetitive lifting is a whole-body exertion. Despite this, the roles and physical exposures of the upper extremities are frequently neglected. The influence of precision requirements and cognitive distractions on upper extremity responses when lifting was evaluated by quantifying several biomechanical upper extremity quantities. Nine participants completed four 30-min lifting tasks with and without simultaneous cognitive distractions and/or precision placement constraints. Specific metrics evaluated were joint reaction forces and moments (wrist, elbow and shoulder) and modelled shoulder muscle forces (38 defined shoulder muscle mechanical elements). The addition of a precision requirement increased several metrics by up to 43%, while the addition of the cognitive distraction task had minimal influence. Furthermore, several metrics decreased by up to 14% after the first 10 min of lifting, suggesting a temporal change of lifting strategy., Practitioner Summary: Lifting tasks often include precision placements and cognitive demands. This study shows that precision placement during prolonged repetitive lifting increases upper extremity forces and moments, while the addition of a cognitive task is benign. Furthermore, field assessments of repetitive lifting should include observations longer than 10 min, as adaptive strategies appear to be adopted.

The impact of exercise on firefighter job performance and cardiorespiratory fitness has been studied extensively, but its effect on musculoskeletal loading remains unknown. The aim of this study was to contrast the physical fitness and low-back loading outcomes of two groups of firefighters who completed different exercise programmes. Before and after 12 weeks of exercise, subjects performed a physical fitness test battery, the Functional Movement Screen™ (FMS) and simulated job tasks during which peak L4/L5 joint compression and reaction shear forces were quantified using a dynamic biomechanical model. Subjects who exercised exhibited statistically significant improvements (p < 0.05) in body composition, cardiorespiratory fitness, muscular strength, power, endurance and flexibility, but FMS scores and occupational low-back loading measures were not consistently affected. Firefighters who are physically fit are better able to perform essential job duties and avoid cardiac events, but short-term improvements in physical fitness may not necessarily translate into reduced low-back injury risk.

Background: Theoretical and empirical data support the notion that distal lower extremity joint dysfunction could influence the low-back injury potential of workers, but the impact of unilateral ankle immobilization on low-back loading during lifting has yet to be examined., Objective: To examine the influence of unilateral ankle immobilization on the kinematics and kinetics of lifting., Methods: With and without their right ankle immobilized, 10 men performed laboratory-simulated occupational lifting tasks. Together with force platform data, three-dimensional kinematics of the lumbar spine, pelvis, and lower extremities were collected, and a dynamic biomechanical model was used to calculate peak compressive and shear loads imposed on the L4/L5 intervertebral joint., Results: In comparison to the unaffected conditions, ankle immobilization generally resulted in less knee (0.001 ≤ p ≤ 0.07) and greater lumbar spine (0.001 ≤ p ≤ 0.35) sagittal motion when lifting. Associated with this compensatory movement strategy were greater L4/L5 anterior/posterior reaction shear forces (0.001 ≤ p ≤ 0.25). However, there were cases when individual compensatory movement strategies differed from the "group" response (i.e., subjects increased their sagittal knee motion on the affected side about 8% of the time); this resulted in increased peak L4/L5 joint compression forces without changing the peak L4/L5 anterior-posterior shear forces., Conclusions: Ankle dysfunction can alter the way in which individuals move and load their low-backs when lifting. The different ways in which individuals compensate for personal movement constraints could alter the potential site and mechanism of occupational low-back injury.

Sustained maximum lumbar spine flexion can increase the angle at which the low back flexion relaxation phenomenon (FRP) is observed. This adaptation has been hypothesized to have implications for the control of lumbar spine stability and increase the potential for low back injury. The objective of this study was to investigate if similar changes in the FRP would occur from sub-maximal spine flexion induced by an extended continuous duration of seated office deskwork. Twenty-three participants (12 male and 11 female) performed three bouts of full forward spine flexion interspersed with two 1-h periods of seated deskwork. Lumbar spine angular kinematics and electromyographic activity from the lumbar erector spinae were obtained throughout all trials. The angles at which myoelectric silence occurred (FRP onset) were documented. Lumbar flexion at FRP onset increased by 1.3±1.5° after 1-h of sitting (p<0.05) with no further increase after 2-h. However, when the angle at the FRP onset was normalized to the total range of flexion, there was no difference in the FRP onset. These results suggest that the seated posture may induce residual deformation in the viscoelastic passive tissues of the low back; this could increase the challenge of controlling spine motion and reduce the load-bearing capacity of the lumbar spine system during activities performed following extended bouts of sitting., (Copyright © 2013 Elsevier Ltd. All rights reserved.)

The purpose of this study was to examine the impact of wearing a resistance band around the distal thigh on frontal plane knee mechanics during bodyweight squat and jumping exercises. Three closed-kinetic-chain exercises were examined, including: (1) bodyweight squat, (2) countermovement jump, and (3) squat jump. For each exercise, three experimental conditions were tested: (1) control condition with no band; (2) light-tension band applied around the distal thighs; and (3) medium-tension band applied around the distal thighs. Two dependent measures were used for analyses: (1) knee width normalized to ankle width and (2) peak external knee moment. In the absence of any feedback, application of the resistance bands failed to promote 'neutral' knee alignment when squatting and jumping. The stiffest resistance band resulted in significantly lower (p = 0.002) peak-width index values during the ascent phase of the countermovement jump. Additionally, the use of the medium-tension band resulted in significantly larger (p = 0.002) peak knee abduction moments compared to the no bands condition during the descent portion of the bodyweight squat and countermovement jump exercises. These findings conflict with previous clinical case reports on the proprioceptive response induced by resistance bands.

The Functional Movement Screen™ (FMS) has demonstrated some efficacy in the prediction of injuries and is thus used by many practitioners to make recommendations for exercise. However, questions remain regarding its utility as a means to evaluate the effectiveness of training. Sixty firefighters volunteered to participate, and their FMS scores were examined before and after 12 weeks of training. Individuals were graded on how they chose to perform rather than how they could perform. The participants were assigned to 1 of 3 groups: intervention 1, intervention 2, or control. The 2 intervention groups received three 1.5-hour training sessions each week and differed in the emphasis that was placed on movement quality. Sagittal and frontal plane videos were used to grade the FMS with 3 methods: the standard 0-3 scale, a 100-point scale that weighted specific compensations (research standard), and a modified 100-point scale whereby grades were assigned based on the total number of compensations present. There were no significant differences in the total FMS scores for any group posttraining. However, the scores of 85% of the firefighters who did not receive training did change. The 100-point scale methods resulted in more FMS score changes posttraining, but the between-group interactions were identical to those found with the standard scoring method. The control group's scores were not consistent pretraining and posttraining; thus, the influence of each intervention could not be evaluated. Currently, the FMS might provide a momentary impression of general movement quality, although further efforts would likely assist in the development of better ways to implement the test, interpret the results, and generate reliable scores.

Workers are often required to perform manual materials handling tasks immediately following periods of prolonged sitting either as a secondary job component of as different tasks in a job rotation strategy. The goal of this investigation was to determine if changes to low-back kinetics and/or kinematics occurred during repetitive lifting/lowering exertions following extended seated exposures. Upper body kinematics, lumbar spine flexion angle, pelvic orientation and bilateral muscle activity from the external abdominal obliques and lumbar erector spinae were recorded for 8 males and 8 females while they alternated between sessions of repetitive lifting/lowering and prolonged sitting. Upper body kinematics were used as inputs to a linked segment model to compute low-back flexion/extension moments, compression, and shear. Peak lumbar flexion was reduced by 1.8 degrees during the lifting/lowering exertions following the first hour of sitting which consequently led to a reduction of approximately 50N in the reaction anteroposterior shear forces. Sitting postures were consistent with previously reported data. The reduced shear loads during repetitive lift/lower exertions following prolonged sitting may be a consequence of alterations in passive tissue properties which could alter the risk of low-back injury, although future research is required to examine the biomechanical significance of this finding. Changes to both kinematics and kinetics were minimal suggesting that using prolonged sitting as a component of a task series in job rotation does not alter the risk present when combined with repetitive lifting tasks.

Push-up exercises are normally performed to challenge muscles that span upper extremity joints. However, it is also recognized that push-ups provide an effective abdominal muscle challenge, especially when the hands are in contact with a labile support surface. The purpose of this study was to compare trunk muscle activation levels and resultant intervertebral joint (IVJ) loading when standard and suspended push-ups were performed, and to quantify and compare the contribution of trunk muscles to IVJ rotational stiffness in both exercises. Eleven recreationally trained male volunteers performed sets of standard and suspended push-ups. Upper body kinematic, kinetic, and EMG data were collected and input into a 3D biomechanical model of the lumbar torso to quantify lumbar IVJ loading and the contributions of trunk muscles to IVJ rotational stiffness. When performing suspended push-ups, muscles of the abdominal wall and the latissimus dorsi were activated to levels that were significantly greater than those elicited when performing standard push-ups (p<.05). As a direct result of these increased activation levels, model-predicted muscle forces increased and consequently led to significantly greater mean (p=.0008) and peak (p=.0012) lumbar IVJ compressive forces when performing suspended push-ups. Also directly resulting from the increased activation levels of the abdominal muscles and the latissimus dorsi during suspended push-ups was increased muscular contribution to lumbar IVJ rotational stiffness (p<.05). In comparison to the standard version of the exercise, suspended push-ups appear to provide a superior abdominal muscle challenge. However, for individuals unable to tolerate high lumbar IVJ compressive loads, potential benefits gained by incorporating suspended push-ups into their resistance training regimen may be outweighed by the risk of overloading low-back tissues.

Background Context: Prolonged sitting may alter the passive stiffness of the lumbar spine. Consequently, performing full lumbar flexion movements after extended periods of sitting may increase the risk of low back injury., Purpose: The purpose was to quantify time-varying changes in the passive flexion stiffness of the lumbar spine with exposure to prolonged sitting and to link these changes to lumbar postures and trunk extensor muscle activation while sitting. A secondary objective was to determine whether men and women responded differently to prolonged sitting., Study Design: Passive lumbar flexion moment-angle curves were generated before, during and after 2 hours of sitting. Lumbar flexion/extension postures and extensor muscle activation levels were measured while sitting., Sample: Twelve (6 men, 6 women) university students with no recent low back pain were studied., Outcome Measures: Quantified changes in the shapes of the passive flexion moment-angle curves (slopes, breakpoints and maximum lumbar flexion angles) were the outcome measures. While sitting, average lumbar flexion/extension angles, the distribution of lumbar flexion/extension postures, average electromyogram (EMG) amplitude, the number and average length of EMG gaps, and trunk extensor muscle rest levels were measured., Methods: Participants performed deskwork for 2 hours while sitting on the seat pan of an office chair. Moment-angle relationships for the lumbar spine were derived by pulling participants through their full voluntary range of lumbar flexion on a customized frictionless table., Results: Lumbar spine stiffness increased in men after only 1 hour of sitting, whereas the responses of women were variable over the 2-hour trial. Men appeared to compensate for this increase in stiffness by assuming less lumbar flexion in the second hour of sitting., Conclusions: Changes in the passive flexion stiffness of the lumbar spine may increase the risk of low back injury after prolonged sitting and may contribute to low back pain in sitting.

Objective: To quantify the time-varying stiffness and kinematic responses of the in vivo lumbar spine exposed to dynamic repetitive flexion movements., Design: Changes in in vivo passive lumbar moment-angle relationships were monitored in response to dynamic repetitive flexion., Background: While previous in vitro studies have provided conflicting evidence on the effects of repetitive flexion movements on the stiffness of the lumbar spine, no previous studies have quantified the time-varying changes of the in vivo lumbar spine to dynamic repetitive flexion., Methods: Subjects lifted and lowered a 4.5 kg load over two barriers at a rate of 7 lifts per minute for 1.5 h inducing at least 80% of the lumbar flexion range of motion. Prior to lifting and at 30 min intervals passive moment-angle relationships were obtained by pulling the subject into flexion on a customized frictionless table., Results: Repetitive lifting induced a decreasing stiffness trend after 30 min, followed by a recovery towards initial stiffness levels with further loading. The trends were non-significant for all measures studied., Conclusions: The results indicate that after 30 min of lifting, creep within the passive tissues may allow workers to exceed their initial range of motion, altering joint mechanics and loading patterns potentially leading to an increased risk of developing low back pain., Relevance: Given the potential for time-varying changes to alter the spine's risk of injury and injury mechanisms, knowledge regarding the stiffness response of the in vivo lumbar spine exposed to repetitive flexion may lead to improved understanding and prevention of work related back pain.

Continuous passive motion (CPM) has been proposed as a method to help individuals with low back pain cope with prolonged sitting. The purpose of this study was to investigate the effects that a commercially available CPM device had on lumbar and thoracic erector spinae (ES) muscle activation (using surface electromyography, "EMG"), and on subjective discomfort during prolonged seated computer work with and without the use of the CPM device. There were no significant differences in average ES muscle activation levels, amplitude probability distribution functions, and EMG gaps number and length when sitting with the CPM device was compared to sitting normally. Subjective ratings of discomfort were also not significantly different between the two sitting conditions. The results indicated that there were no clear mechanisms by which the CPM device may reduce ES muscle pain and fatigue for the tasks and pain-free individuals studied.