ABSTRACT
Shoulder disorders and complaints constitute an important health problem in the working population. Research on shoulder muscle loading temporal change during low-intensity repetitive motion is limited. The goal of this paper was to evaluate the temporal pattern of shoulder muscle activities during a repetitive reaching task, and to compare the patterns observed in a younger and older group. Twenty participants completed an 80 min unloaded reaching task and the surface electromyography of upper trapezius and posterior deltoid muscles were recorded continuously. Both upper trapezius and posterior deltoid showed signs of localized muscle fatigue including increased amplitude and decreased median power frequency over the 80 min task. Muscle fatigue development was faster and greater in the older group than the younger group.
