Central regulation of physical fatigue via mirror visual feedback

Central fatigue refers to a progressive decline in the ability to activate muscles voluntarily. Although fatigue-related inhibitory input to the motor cortex from group III and IV afferents that carry sensory information is thought to contribute to the fatigue-related changes in the motor cortex, other sites effectively driving the motor cortex during physical fatigue have not been identified. Contribution of a mirror visual feedback system to regulate physical fatigue was examined. The study group consisted of 12 healthy participants who performed 60 repetitive left handgrips at maximal voluntary contraction every 1 s as a fatigue-inducing physical task session. Before and after the session, left and right handgrip forces were measured for fatigue evaluation. After the fatigue-inducing task session, handgrip forces of the right and left hands were reduced. Although there was no difference in the reduced level of the handgrip force of the right hand between the sessions with and without a Ramachandran's mirror box, that of the left hand was attenuated by watching the mirror of the mirror box. A mirror visual feedback system is involved in the mechanisms regulating physical fatigue.