Ergonomic interventions for commercial crab fishermen

Work tasks in the commercial fishing industry require strength, endurance and coordination and these tasks expose fishermen to many of the recognized risk factors for the development of work-related musculoskeletal disorders. The focus of the current study was the design, development and testing of two simple ergonomic interventions to reduce exposure to these risk factors in small-scale commercial crab fishermen. In a laboratory study of these interventions, EMG and motion analysis systems were used to quantify changes in muscle force and body postures. The results of laboratory evaluation of the intervention designed to reduce the low back stress associated with hoisting the crab pots onboard showed significant reductions in muscle force requirements (erector spinae activity reduced by 25%) and peak sagittal trunk angle (reduced by 34%), while the results of the intervention designed to reduce shoulder stress during the process of shaking the crabs from the pots showed significant reductions in peak deltoid activity (reduced by 24%). A field test of these interventions provided a more subjective “usability” evaluation of the interventions. These responses were cautiously positive, providing insights into when these interventions would be most appropriate and under what conditions they would be more of a hindrance than a help. Relevance to industry Engineering controls are recognized as the most effective methods of reducing exposure to risk factors for musculoskeletal injury. Engineering controls were developed for small-scale commercial crab fishermen and these interventions were tested in the laboratory and in the field.This is a manuscript of an article from International Journal of Industrial Ergonomics, 41: 481-487, (DOI:10.1016/j.ergon.2011.03.006). © 2011. This manuscript version is made available under the CC-BY-NC-ND 4.0 license http://creativecommons.org/licenses/by-nc-nd/4.0/</p

An in vivo assessment of the low back response to prolonged flexion: Interplay between active and passive tissues

Background: Full flexion lumbar postures maintained over a prolonged period of time have been shown to lead to changes in the supporting passive structures of the spine and it has been hypothesized that this may lead to low back pain/disorders. However, the specific biomechanics and physiology of this link have not been fully developed. Of particular interest is the interplay between the active and passive extensor mechanisms and the role of rest break in this response. Methods: Ten healthy participants performed a regimen of a 10-min full lumbar flexion followed by a 10-min upright standing, with a slow speed isokinetic lift every 2.5 min. Changes in the full lumbar flexion angle (system creep) and the electromyographic activity of back extensors in the isokinetic lifts were evaluated. Findings: Results showed significant increases in the full flexion angle and increased activity of the extensor muscles in the prolonged flexion to compensate for the reduced extension moment producing capability of the passive tissues. A 30-s rest break in the middle of the flexion moderated these viscoelastic responses. Interpretation: The results suggest that prolonged lumbar flexion results in the systematic transfer of an extension moment from passive tissues to active muscles. Heavy lifting or high force exertion of back muscles immediately after prolonged flexion could be a risk factor for low back disorders when the muscles lose their force generating capacity due to passive stretching. This study also indicated the importance of sufficient rest between consecutive full flexion tasks in reducing the risk.close353

Viscoelastic responses of the lumbar spine during prolonged stooping

There is considerable evidence that awkward postures of the low back are related to the incidence of low back disorders (LBDs), but the specific biomechanics/physiology of this link is not fully developed. This study combined empirical work with finite element analyses to explore this relationship. The empirical work focused on quantifying the time-dependent responses of the lumbar spine during a prolonged stooped posture by assessing the changes in the sagittal plane range of motion and the electromyographic activity of the back extensor musculature during and after prolonged stooping. Ten healthy participants performed a regimen of a 10 minute stooping period followed by a 10 minute upright standing recovery period, with an isokinetic lift at every 2.5 minutes. Results showed significant creep effects of the flexion angle and the increased activity of extensor muscles in stooping to compensate for the reduced extensor moment producing capability of the passive tissues. The 10 minute upright standing did not produce a full recovery of the lumbar spine tissues but a 30 second rest break in the middle of the stooping moderated these viscoelastic responses. A nonlinear viscoelastic 3D finite element (FE) model of the lumbar spine was developed to predict the responses of the passive and active tissues of the low back. Validation of the FE model by comparing its predicted results (range of motion, muscle activation levels, etc.) with experimental results indicated good agreement in terms of mechanical behaviors in stooping, confirming the capability of the FE model as a potential tool for risk assessment of the prolonged stooping tasks

Differences in trunk kinematics and ground reaction forces between older and younger adults during lifting

Age-related changes in trunk kinematics in lifting have received little attention despite a documented increased risk of musculoskeletal injury with age. This study examined the responses in trunk kinematics and ground reaction forces of older and younger subjects during lifting. Ten older (55-63 years) and ten younger (19-29 years) adults performed lifting tasks in six different conditions. A lumbar motion monitor was used to measure the subjects&apos; trunk kinematics and a force platform was used to measure the ground reaction forces during the lifting motion. The results of this study showed that age had a significant (p&lt;0.05) effect on the transverse plane (axial twisting) trunk kinematics variables (peak velocity and peak acceleration) but did not affect ground reaction forces or other trunk kinematics variables. The peak transverse velocity was 40% lower and peak transverse acceleration was 30% lower in the older subjects as compared to the younger subjects. Relevance to industry: This study presents the postural adaptation of older subjects to dynamic lifting tasks. Results can be used to understand the risks of older work population in manual material handling tasks.close7

Differences in Trunk Kinematics and Ground Reaction Forces between Older and Younger Adults during Lifting

Trunk kinematics, ground reaction forces, and the motion of the center of pressure (COP) of older and younger subjects were compared in lifting to study age-related differences between the two age groups. Ten older (55 - 63 years old) and ten younger (19 - 29 years old) adults performed lifting tasks under six different conditions; three destination heights and two asymmetry angles of origin. Subjects&apos; trunk kinematics, ground reaction forces and COP motions were measured by the Lumbar Motion Monitor (LMM) and a force plate. Older subjects showed significantly less trunk kinematics, peak ground reaction forces, and COP motions than younger subjects, indicating older subjects chose more stable lifting strategy and it might compensate for the decreased ability of postural control over age. Less ground reaction forces and motion of COP suggested that risks of falls and slips of older subjects were less than younger subjects