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.
Acknowledgements
The authors are grateful to Birthe Lundager (Social Medicine Unit, Aalborg Hospital) and Lars Arendt-Nielsen (Centre for Sensory-Motor Interaction, Aalborg University). This work was financially supported by Arbejdsmilj⊘forskningsfond, Det Obelske Familiefond, Norma og Frode S. Jacobsens Fond, Sygekassernes Helsefond and the Danish National Research Foundation.