Objectives: The purpose of this prospective laboratory study was to follow newly employed workers in the fish or poultry industry for 6 months and investigate possible changes in sensory manifestations and motor performance during low load, repetitive work simulation. It was investigated whether the changes were an effect of employment duration and of development of neck-shoulder complaints.
Methods: Twelve newly employed female filleting employees without any sign of neck-shoulder tenderness/pain at the time of employment of 0 months took part in two laboratory recording sessions planned within 1 month of employment and after 6 months of employment at the plant. After 6 months, six workers out of 12 had developed pain and/or tenderness in the neck-shoulder region. The recording sessions evaluated sensory-motor aspects by measuring pressure pain threshold, work-task timing, cutting forces, surface electromyographic activity of four shoulder muscles, displacement of the centre of pressure, and 3D movements of the arm and trunk during simulation of low load, repetitive filleting.
Results: Effects due to the duration of employment were observed in both groups, i.e. decreased sensibility to pressure, decrease in the duration of the work cycle, increased arm starting position with respect to the upright position, and decreased range of motion of the arm and trunk (P<0.05) after 6 months. Among the workers with neck-shoulder complaints, increased sensibility to pressure, lower force level, higher electromyographic activity, decreased amplitude of arm movement, and increased trunk posture and movement amplitude (P<0.05) were observed, compared with workers without complaints.
Conclusions: Differences in terms of sensory manifestations and motor control strategy were seen after 6 months of employment with or without neck-shoulder complaints. In general, changes in sensory manifestations and motor control strategy after 6 months work were most likely of importance, as they underlined a learning process as employment duration increased. Moreover, the present sensory-motor changes observed among workers with neck-shoulder complaints highlighted the potential physical risk factors associated with low load, repetitive work.