The role of cocontraction in the impairment of movement accuracy with fatigue.

The present experiment was designed to test the hypothesis that fatigue-induced impairment in movement accuracy is caused by a decrease in muscle cocontraction rather than a reduced ability to produce muscular force. Seven participants performed fast and accurate elbow extensions aimed at a target, before and after a fatigue protocol. The inertia of the manipulandum was decreased after the fatigue protocol so that the ratio of required to available force during movements was identical pre- and post-fatigue. After the fatigue protocol, movement endpoint accuracy decreased and movement endpoint variability increased. These alterations were associated with a decrease in cocontraction. We concluded that the impairment of movement accuracy during fatigue could not be explained by the lack of available force, but was likely to be due to a fatigue-induced decrease in muscular cocontraction. We then speculate that fatigue influences the relative weights of accuracy and energy economy in the optimisation of sensorimotor control.