The occupation of sheep-shearing is classified as heavy to very-heavy physical work requiring a high level of energy expenditure while performing a repetitive task in a predominantly sustained trunk flexion posture. The task is further complicated by unpredictable animal behaviour. Shearing is considered to carry a high risk of injury particularly to the lumbar spine and epidemiological studies have demonstrated that the prevalence of low back pain (LBP) in shearers is high relative to other occupations. The emergence of a commercial shearing-aid (Warrie Back-Aid TM) that is purported to decrease loading on the spine, reduce injury rate and alleviate symptoms of spinal origin has been welcomed by many sectors of the wool-harvesting industry. However, the precise biomechanical influence of the Warrie Back-Aid TM (WBA) on the sheep-shearing task has not been quantified. The purpose of this study was to investigate the effect of the WBA on three-dimensional kinematics and electromyography of the trunk for 12 experienced shearers during the occupational task of sheep-shearing. Sheep-shearing is a highly patterned process comprised of specific interlinked phases. Nine distinct phases of the shearing-task where the harness was worn during the removal of the sheep�s fleece were investigated. The study used an opto-electronic motion analysis system and rigid body dynamic modelling. The shearer�s trunk and pelvis were considered as a series of three coupled rigid segments; pelvis, lumbar, and thorax with four passive retro-reflective markers defining each segment. The kinematic variables of angular displacement, velocity and acceleration at the thoraco-lumbar and lumbo-pelvic joint centres were calculated for each shearer while shearing with and without the WBA. An eight channel sEMG telemetry system was used to simultaneous record activity in four pairs of trunk muscles. Temporal analysis of the sEMG signal gave information on the duration and relative intensity of trunk muscle activity. The results demonstrated that the task of sheep-shearing required endurance-based muscle activity and the adoption of quasi-static posturing combined with complex asymmetrical trunk motion for extensive periods of the task time. There was considerable variability in the trunk motion of individual shearers despite the pattern-taught and repeatable nature of the shearing task. The introduction of the WBA had no effect on the time taken to shear or trunk kinematics however it resulted in reductions in muscular activity of the trunk extensors. When the complete shearing task was analysed there was a statistically significant reduction in mean intensity of muscle activity for the left multifidus (p = 0.010), right multifidus (p = 0.001), right iliocostalis (p = 0.004) and right longissimus (p = 0.002) when the WBA was used. A reduction in muscular activity of the trunk extensors during the sheep-shearing task may result in a decrease in spinal loading, energy expenditure and muscular fatigue. The clinical recommendation based on the biomechanical results of this and other studies is that the WBA should be incorporated into the practice of sheep-shearing to assist in the reduction of inherent risks associated with the shearing task. Prospective studies into the effect of the harness on LBP are required to endorse this recommendation.

The occupation of sheep-shearing is classified as heavy to very-heavy physical work requiring a high level of energy expenditure while performing a repetitive task in a predominantly sustained trunk flexion posture. The task is further complicated by unpredictable animal behaviour. Shearing is considered to carry a high risk of injury particularly to the lumbar spine and epidemiological studies have demonstrated that the prevalence of low back pain (LBP) in shearers is high relative to other occupations. The emergence of a commercial shearing-aid (Warrie Back-Aid TM) that is purported to decrease loading on the spine, reduce injury rate and alleviate symptoms of spinal origin has been welcomed by many sectors of the wool-harvesting industry. However, the precise biomechanical influence of the Warrie Back-Aid TM (WBA) on the sheep-shearing task has not been quantified. The purpose of this study was to investigate the effect of the WBA on three-dimensional kinematics and electromyography of the trunk for 12 experienced shearers during the occupational task of sheep-shearing. Sheep-shearing is a highly patterned process comprised of specific interlinked phases. Nine distinct phases of the shearing-task where the harness was worn during the removal of the sheep�s fleece were investigated. The study used an opto-electronic motion analysis system and rigid body dynamic modelling. The shearer�s trunk and pelvis were considered as a series of three coupled rigid segments; pelvis, lumbar, and thorax with four passive retro-reflective markers defining each segment. The kinematic variables of angular displacement, velocity and acceleration at the thoraco-lumbar and lumbo-pelvic joint centres were calculated for each shearer while shearing with and without the WBA. An eight channel sEMG telemetry system was used to simultaneous record activity in four pairs of trunk muscles. Temporal analysis of the sEMG signal gave information on the duration and relative intensity of trunk muscle activity. The results demonstrated that the task of sheep-shearing required endurance-based muscle activity and the adoption of quasi-static posturing combined with complex asymmetrical trunk motion for extensive periods of the task time. There was considerable variability in the trunk motion of individual shearers despite the pattern-taught and repeatable nature of the shearing task. The introduction of the WBA had no effect on the time taken to shear or trunk kinematics however it resulted in reductions in muscular activity of the trunk extensors. When the complete shearing task was analysed there was a statistically significant reduction in mean intensity of muscle activity for the left multifidus (p = 0.010), right multifidus (p = 0.001), right iliocostalis (p = 0.004) and right longissimus (p = 0.002) when the WBA was used. A reduction in muscular activity of the trunk extensors during the sheep-shearing task may result in a decrease in spinal loading, energy expenditure and muscular fatigue. The clinical recommendation based on the biomechanical results of this and other studies is that the WBA should be incorporated into the practice of sheep-shearing to assist in the reduction of inherent risks associated with the shearing task. Prospective studies into the effect of the harness on LBP are required to endorse this recommendation.