Motor cortical excitability and inhibition are differentially modulated by aerobic exercise intensity.

Acute aerobic exercise (AEX) enhances motor learning and promotes neuroplasticity. Although previous studies examined the impact of AEX on primary motor cortex (M1) excitability, the dose-response relationship across a broad intensity spectrum with consistent exercise parameters remains to be fully elucidated. This study investigated the impact of AEX intensity on distinct M1 circuits using transcranial magnetic stimulation (TMS). Thirty right-handed adults underwent four experimental sessions: 20-min rest (control), light (LIIT: 35% heart rate reserve [HRR]), moderate (MIIT; 55% HRR), and high-intensity interval training (HIIT; 80% HRR) AEX. The interval cycling sessions alternated between 3 min at the target intensity and 2 min of active recovery (25% HRR). We performed TMS measures before (Pre), immediately post (Post0), and 20-min post (Post20) AEX/rest to assess corticospinal excitability and short-interval intracortical inhibition (SICI). We found that: (i) HIIT and MIIT increased corticospinal excitability, with HIIT eliciting a sustained increase, and (ii) all AEX intensities (LIIT, MIIT, HIIT) decreased SICI, with the greatest sustained reduction following MIIT. Altogether, our results demonstrate the impact of HIIT and MIIT to enhance corticospinal excitability and reduce SICI in M1. This study provides evidence for a dose-response effect of AEX intensity on the modulation of distinct M1 circuits.