Toward Standardized Protocols: Determining Optimal Stimulation Volumes for 5 Hz Repetitive Peripheral Magnetic Stimulation (rPMS) of the Tibial Nerve—A Controlled Exploratory Study

Background: Repetitive peripheral magnetic stimulation (rPMS) has emerged as a promising non-invasive treatment modality for reducing muscle hypertonus and spasticity. However, standardized protocols regarding stimulation parameters, particularly the number of stimuli required to achieve therapeutic effects, remain largely undefined. Methods: In an exploratory study, seventeen healthy participants (15 male, 2 female) underwent progressive rPMS treatments at 5 Hz frequency with incrementally increasing stimulus counts (105, 210, 315, 420, and 840 stimuli). Seventeen participants served as controls (11 male, 6 female) receiving sham stimulation. Achilles tendon reflexes were elicited using a computer-controlled reflex hammer, and compound muscle action potential (CMAP) peak-to-peak amplitudes were recorded via surface electromyography before and immediately after each stimulation session. Results: The overall repeated-measures ANOVA indicated a significant main effect (F(5, 80) = 4.98, p = 0.001, η²_p = 0.237). All rPMS treatments produced significant reductions in CMAP amplitudes compared to baseline (p < 0.05). No progressive dose-dependent relationship was observed between stimulus count and response magnitude, suggesting a threshold effect rather than progressive inhibition. Control group showed no significant changes (p ≤ 0.56). Conclusions: Low-frequency (5 Hz) rPMS produces rapid inhibitory effects on spinal reflex circuits with onset after as few as 105 stimuli. These findings indicate that treatment effects can be achieved with substantially fewer stimuli than previously assumed. Further research is needed to identify parameters capable of achieving greater reflex suppression.