Activity in five muscles during joint securing using pneumatic nutrunners

摘要

Musculoskeletal disorders are common among workers who use powered hand-held tools in assembly in industry. The present study was carried out at a bus assembly plant where pneumatic nutrunners are the dominant powered hand tool. The electromyographic (FMG) activity in five muscles was measured during different phases of the securing, in comparisons of soft and stiff joints, three different joint positions, and two tools. The aims were to characterize the muscular load during usage of the tools, and to provide relevant information to the production engineers, who were to design a new production system. The variance in muscular activity was large, both within subjects and between the mean curves of different subjects. Still, it was possible to obtain characteristic shapes of EMG curves sampled under different conditions. The EMG peaks caused by stretch reflexes were seen for the wrist extensor muscles, and trapezius muscles, for a right-angled tool. Unloading reflexes were noticed for the erector spinae and the trapezius muscles. Joint position strongly contributed to differences in muscular activity in all five muscles, which together with the finding that the tools caused very small differences, were regarded as the most valuable results for the production engineers.