Possible neural mechanisms underlying post-contraction potentiation in elbow flexor muscle in humans

Precise and sequential motor tasks that require strenuous and fine force control involve distinct, complex neural mechanisms without which they would be difficult to perform. A previous study showed that strenuous force exertion gives rise to potentiation of active muscles (post-contraction potentiation, PCP). However, the mechanisms underlying PCP remain unclear. We investigated the neural mechanisms underlying PCP using spectral analyses of surface EMG activity. Fourteen healthy participants were asked to perform an EMG matching task (2% of maximum voluntary contraction, MVC) before (Test 1) and after (Test 2) they exerted a brief 50% MVC (conditioning contraction, CC). The exerted force was significantly lower during Test 2 than Test 1, indicating that PCP did occur. In addition, spike-like EMG responses with a mean frequency of ~10 Hz were frequently observed during Test 2. Power spectrum analysis demonstrated that the peak power of both α and β bands increased after CC, and that changes in the peak power of both bands during Test 2 negatively correlated with changes in force. These findings suggest that the synchronization of active motor units accounted for PCP.