Biomechanics of pointing to a perceived target: Effects of fatigue and gender

Abstract

Neck/shoulder pain, which is more prevalent in women, has previously been linked to repetitive work and muscle fatigue. We have shown that asymptomatic people performing repetitive upper limb tasks display shoulder fatigue and whole-body compensatory strategies. However, the role of proprioception in controlling these patterns is unclear. The perception of muscular effort has been implicated in the proprioceptive aspects of the fatigue response, although few studies have estimated its impact. In this study, a group of asymptomatic adults (9 women, 9 men) performed a repetitive pointing task (RPT) to fatigue. Before and after the RPT, they performed a shoulder position (SPS) task where they abducted their shoulder to the perceived horizontal, and an endpoint position (EPS) task, where they moved their finger to a perceived target location in front of them. In the SPS, subjects made larger errors after fatigue by raising their elbow higher (~ +1.3cm). In a follow-up study, subjects replicating the same task made smaller errors when actively moving their arm to the target, compared to that when the arm was passively moved. As for the EPS, subjects' finger position accuracy was not affected by fatigue. There were no gender effects on accuracy pre- and post-RPT; however, there were gender differences in the perceived finger target location and in the temporal characteristics of movement towards 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 multijoint task constant, possibly by using feedback from muscle output. Movement strategies and perception of endpoint location may play parts in gender differences in work-related neck/shoulder symptoms. © 2011 Springer-Verlag.