Effect of muscle fatigue on target positioning of the human forearm under conditions of restriction of visual control

We studied movements of the forearm within the limits of 0 deg (full extension)-flexion to a 100 deg angle in the elbow joint-a reverse movement with episodes of target positioning at an intermediate target level (50 deg). The standard trajectory and trajectory of the performed movement were visualized by movements of cursors on the screen of a monitor in joint angle vs time coordinates. Systematic errors of blindfold (kinesthetic) positioning (after removal of the visual feedback informing the subject on the characteristics of the performed movement) observed under control conditions and after realization of a fatigue-inducing series of flexions/extensions of the forearm with a high loading were compared. It was found that the development of fatigue evoked no fundamental changes in the pattern of systematic errors of kinesthetic positioning. Both considerable prevailing of positive systematic errors within the examined group, their high interindividual variability, and (in most cases) patterns of signs of errors after reaching the target level by movements of opposite directions typical of the given subject were preserved. Mean intragroup values after the development of fatigue demonstrated some trend toward a decrease, but these changes did not reach the significance level. Possible mechanisms of the influence of muscle fatigue on the process of target positioning of a limb link realized exclusively under proprioceptive control are discussed.