The effect of muscle fatigue on position sense in an upper limb multi-joint task.

The purpose of this study was to estimate the extent to which muscle fatigue can impact on the position sense in the upper limb. Twelve healthy volunteers were asked to do a reaching task while grasping a wooden block and match the block's position with a corresponding target displayed on a flat screen, without vision. Following that, subjects performed resistive exercises with Thera-band strips until fatigue was induced and then the position sense task was repeated. A significant change in the endpoint position was observed after fatigue, in the up/down direction (p ≤ .001). The variability of endpoint positions in up/down direction was also significantly increased after fatigue (p ≤.03). There was no significant change in endpoint orientation but there was a significant fatigue × orientation effect on endpoint rotational variability. In a follow-up experiment, a group of subjects repeated the same protocol, but with a period of quiet rest between the two position sense tasks. In that group, there were no differences in endpoint position, orientation or variability. Muscle fatigue is an important factor that should be taken into consideration during the treatment of musculoskeletal injuries as well as athletic training.