The size of cycle-to-cycle variability in biomechanical exposure among butchers performing a standardised cutting task

Abstract

The effects of employment duration and pain development on motor variability were investigated during repetitive work. Electromyographic (EMG) and kinematics data from two previous studies were re-analysed. Newly employed butchers were followed prospectively in relation to employment duration and pain development. Healthy butchers with long-term experience were compared with novices. The variability of the cycle time, EMG ratio and arm and trunk movement was expressed as cycle-to-cycle standard deviations. During the first 6 months of employment, cycle time variability decreased, while posture and movement variability increased (p < 0.05). In presence of pain, the variability of the initial arm position decreased while it increased for the trunk (p < 0.05). Experienced butchers showed a larger variability than novices for work cycle and several kinematic variables, but a smaller EMG ratio variability (p < 0.05). These findings indicate that the variability of motor patterns in repetitive work changes with experience and pain. A change towards a more variable motor strategy may protect workers from work-related musculoskeletal disorders.