Effects Of Theta Burst Stimulation To The Supplementary Motor Area On Upper Limb Muscle Output Characteristics And Corticospinal Excitability

Effort perception during physical activity varies associated to physical and mental states. In sports, increased effort perception leads to reduced performance and heightened fatigue. Therefore, it is crucial to elucidate the mechanisms underlying effort perception related to exercise. PURPOSE: The study aimed to investigate the effects of theta burst transcranial magnetic stimulation (TBS) to the supplementary motor area (SMA)—a region associated with effort perception (Zénon+, 2015)—on upper limb muscle output characteristics and corticospinal excitability. METHODS: Ten healthy adults received continuous TBS (cTBS) with inhibitory effects and intermittent TBS (iTBS) with facilitatory effects, administered in a random order. Motor output characteristics were assessed by measuring abduction force of the index finger at a subjective effort level of 35% (5 seconds) without visual feedback, and the coefficient of variation (CV) of a force-matching task of index finger abduction to 10% maximal force with visual feedback. Corticospinal excitability was evaluated at rest with motor-evoked potentials in the first dorsal interosseous (FDI) muscle. These evaluations were performed at pre-TBS and at 0-, 15- and 30-minutes post-TBS. Post-TBS values were normalized by pre-TBS values, and Friedman tests with four time points conducted each for cTBS and iTBS. RESULTS: For the 35% effort force task, there was no significant main effect for cTBS [χ2 (2) = 2.40, p = 0.301]. However, a significant main effect was observed for iTBS [χ2 (2) = 8.04, p = 0.045], with the post hoc Durbin-Conover tests indicating significant decrease of 35% effort force in 0, and 15 min after iTBS, compared to pre values (post0min-TBS, 84 ± 24 % pre, p = 0.018; post15min-TBS, 79 ± 17 % pre, p = 0.007). No significant effects were found for CV in the force-matching task or corticospinal excitability (both, p > 0.05). CONCLUSION: Our findings suggest that iTBS to SMA increase perceived effort levels during upper limb movements. This effect could inform the development of training and rehabilitation methods aimed at optimizing effort perception for athletes.