Cerebellar transcranial static magnetic field stimulation reduces muscle activity during maximum contraction.

BACKGROUND: Transcranial static magnetic field stimulation (tSMS) is a noninvasive technique that modulates neuronal excitability without inducing an electrical current. Although triple-magnet tSMS has been shown to suppress cortical excitability in the motor cortex, its effects on cerebellar circuits and motor output remain unclear. OBJECTIVE: We examined whether cerebellar triple-magnet tSMS modulates voluntary muscle activation, cortical excitability, cerebellar output in healthy adults. METHODS: In this single-blind, randomized, sham-controlled study, 44 healthy participants received real- or sham-tSMS over the right cerebellum. Motor output was assessed by electromyography (EMG) of the right first dorsal interosseous muscle during maximum voluntary contraction (MVC). The resting motor threshold (rMT) and cerebellar brain inhibition (CBI) were measured using transcranial magnetic stimulation. RESULTS: EMG activity during MVC decreased in both groups, with a greater reduction in the real-tSMS group (p = 0.008, r = 0.402). No significant effect of tSMS was observed on the rMT or CBI. CONCLUSION: Cerebellar triple-magnet tSMS reduced EMG activity during MVC, suggesting modulation of voluntary motor control. The absence of changes in rMT and CBI suggests that tSMS may act via mechanisms not captured by conventional physiological indices. Trial registration UMIN Clinical Trials Registry UMIN000058833 Date of registration 19 August 2025. Retrospectively registered.