Unilateral Vibratory Stimulation Inhibits Contralateral Spinal Anterior Horn Cells in Homonymous Muscles for the First 75 Seconds

Objective: To investigate muscle tone changes over time in contralateral homonymous muscles when unilateral muscles are stimulated, using F-wave measurements, we examined whether vibratory stimulation on the contralateral homonymous muscle of the affected side may reduce spasticity, whose optimal duration remains unclear.Methods: Vibratory stimulation was applied to the right hand of healthy adults, using parameters of 80 Hz frequency, 0.4 mm amplitude, 400 g load, and 195 seconds of duration on the abductor digiti minimi muscle. F-wave was measured in the left hand before stimulation, at seven intervals during stimulation, and immediately after.Results: The F/M amplitude ratio decreased immediately at stimulation onset, at 30 seconds, and at 60 seconds compared to baseline. A least-squares analysis revealed a negative slope from baseline to 60 seconds (f(x)=-0.11x+1.12), while the slope became positive after 90 seconds, continuing after stimulation ended (f(x)=0.04x+0.82).Conclusion: Unilateral vibratory stimulation may decrease excitability in the spinal anterior horn cells of the contralateral homonymous muscle for up to 75 seconds post-stimulation, suggesting a potential mechanism for spasticity management.