Short-term effects of electrical stimulation and voluntary activity on corticomotor excitability in healthy individuals and people with stroke.

Electrical stimulation (ES) of muscle is often used to augment motor recovery in populations with neurologic disorders. The aim of the study was to examine the changes in corticomotor excitability in response to different forms of ES applied to the wrist extensors. Healthy adults and people with stroke completed three separate test sessions. In each session, 60 wrist extensor contractions were elicited by one of the three interventions: (1) voluntary isometric muscle activation, (2) automated ES, or (3) electromyography-triggered ES. Motor evoked potentials were significantly increased after the voluntary contraction and electromyography-triggered ES interventions, but not after automated ES, in healthy participants. There was no significant change in motor evoked potential amplitude after any of the interventions in the participants with chronic stroke. Using the ES parameters of this study, voluntary drive was required to induce change in corticomotor excitability in the healthy participants. The stimulation intensity and duration parameters used did not induce any immediate changes in corticomotor excitability in the participants with stroke. The authors conclude that combining voluntary activation with ES may enhance the efficacy of stimulation in healthy adults. Repeated applications or longer durations of stimulation may be necessary to alter neuronal excitability in a stroke population.