Repetitive arm motion-induced fatigue affects shoulder but not endpoint position sense.

Neck/shoulder pain has previously been linked to repetitive work and muscle fatigue. We have shown that asymptomatic people performing repetitive upper limb tasks display signs of shoulder fatigue and of whole-body compensatory strategies. However, the role played by the proprioceptive system in the production of these compensatory strategies has not been studied. A group of asymptomatic adults (n = 18) performed a repetitive pointing task at shoulder height to fatigue. Before and after fatigue, they performed two position sense tasks, eyes closed: a single-joint task where they abducted their shoulder to the perceived horizontal and a multi-joint task, where they stood and placed their finger at the perceived location of a target in front of them at shoulder height. After fatigue, subjects made larger shoulder errors by raising their elbow higher above the horizontal (~ +1.3 cm) than before fatigue; however, their finger position accuracy was not changed, despite all subjects performing the movement in less time (~ -0.18 s) while fatigued. There were no gender differences in shoulder or finger position accuracy before or after fatigue; however, there were gender differences in the perceived finger-target location and in the temporal characteristics of the finger movement toward the target. Results suggest that healthy individuals are able to develop strategies to compensate for fatigue-induced deficits at one joint to maintain the endpoint accuracy of a multi-joint task constant. Gender differences in movement strategies and perception of endpoint location may play parts in the previously reported gender differences in work-related neck/shoulder symptoms.