Electrically-induced muscle fatigue affects feedforward mechanisms of control.

OBJECTIVE: To investigate the effects of focal muscle fatigue induced by electromyostimulation (EMS) on Anticipatory Postural Adjustments (APAs) during arm flexions performed at maximal velocity.

METHODS: Fifteen healthy subjects performed self-paced arm flexions at maximal velocity before and after the completion of fatiguing electromyostimulation programs involving the medial and anterior deltoids and aiming to degrade movement peak acceleration. APA timing and magnitude were measured using surface electromyography.

RESULTS: Following muscle fatigue, despite a lower mechanical disturbance evidenced by significant decreased peak accelerations (-12%, p<.001), APAs remained unchanged as compared to control trials (p>.11 for all analyses).

CONCLUSION: The fatigue signals evoked by externally-generated contractions seem to be gated by the Central Nervous System and result in postural strategy changes which aim to increase the postural safety margin.

SIGNIFICANCE: EMS is widely used in rehabilitation and training programs for its neuromuscular function-related benefits. However and from a motor control viewpoint, the present results show that the use of EMS can lead to acute inaccuracies in predictive motor control. We propose that clinicians should investigate the chronic and global effects of EMS on motor control.