Long-term effects on motor cortical excitability induced by repeated muscle vibration during contraction in healthy subjects.

Objective: The effects of a novel repeated muscle vibration intervention (rMV; 100 Hz, 90 min over 3 consecutive days) on corticomotor excitability were studied in healthy subjects.

Methods: rMV was applied over the flexor carpi radialis (FCR) during voluntary contraction (experiment 1), during relaxation and during contraction without vibration (experiment 2). Focal transcranial magnetic stimulation (TMS) was applied before rMV and one hour, and one, two and three weeks after the last muscle vibration intervention. At each of these time points, we assessed the motor map area and volume in the FCR, extensor digitorum communis (EDC) and abductor digiti minimi (ADM). Short-interval intracortical inhibition (SICI) and facilitation (ICF) were tested for the flexor/extensor muscles alone.

Results: Following rMV under voluntary contraction, we observed a significant reduction in the FCR map volumes and an enhancement in the EDC. SICI was increased in the FCR and reduced in the EDC. These changes persisted for up to two weeks and occurred at the cortical level in the hemisphere contralateral to the side of the intervention.

Conclusion: We conclude that rMV, applied during a voluntary contraction, may induce prolonged changes in the excitatory/inhibitory state of the primary motor cortex. These findings may represent an important advance in motor disorder rehabilitation.