Previous studies have shown that supraspinal excitability is higher during arm cycling than a position- and intensity-matched tonic contraction, but the underlying mechanisms remain unclear. This study aimed to determine whether long-interval intracortical inhibition (LICI) occurs during arm cycling and if LICI differs between arm cycling and tonic contraction. A paired-pulse transcranial magnetic stimulation (TMS) protocol assessed LICI using a supramaximal conditioning pulse that produced a silent period of approximately 150 ms, followed by a test pulse with a 100 ms interstimulus interval. Stimulation occurred at the 4 o'clock position to align the test pulse with the ascending limb of the biceps brachii electromyography profile during the elbow flexion phase. Additionally, a single-pulse TMS stimulation was delivered 100 ms after the 4 o'clock position. Motor-evoked potentials (MEPs) were measured as ratios: a position-matched ratio of test pulse-evoked MEP over single pulse-evoked MEP. MEP ratios were analyzed for peak-to-peak amplitude during arm cycling and tonic contraction. Results showed that LICI was present during arm cycling ( t(13) = 3.5, p < 0.001, 95% CI [−3.2, −0.75]), but no significant difference in LICI was found between arm cycling and tonic contraction ( t(13) = 1.3, p = 0.242, 95% CI [−0.23, −0.06]). These findings suggest that while LICI is present during arm cycling, it is not task-dependent.

Purpose: This study investigated whether an acute bout of submaximal unilateral arm cycling elicits sustained changes in corticospinal excitability (CSE) and short-interval intracortical inhibition (SICI) in the homologous muscles of the non-exercised, resting limb. A secondary aim was to determine whether prior exercise induces a preconditioning effect on subsequent motor output. Methods: Transcranial magnetic stimulation was used to assess motor evoked potential (MEP) amplitude (single-pulse) and SICI (paired-pulse) in the resting non-dominant flexor carpi radialis (FCR) and extensor carpi radialis (ECR) muscles of healthy participants. Measures were obtained at rest, during a 10 min bout of unilateral arm cycling (30 W, 60 rpm), and throughout a 20 min recovery period. To assess potential preconditioning effects, measurements were repeated during a second 2 min cycling bout following a 20 min recovery. Rest and exercise conditions were analyzed separately due to differences in stimulation intensity (RMT vs. AMT). Results: Unilateral arm cycling did not produce sustained changes in CSE or SICI in the resting limb when both arms were at rest. Furthermore, unilateral arm cycling followed by a 20 min recovery period did not result in a preconditioning effect, as CSE in the resting limb was not enhanced during a subsequent unilateral arm cycling bout. Conclusions: Submaximal unilateral arm cycling induces a transient, state-dependent increase in CSE to the non-exercised limb without altering SICI. The absence of SICI modulation suggests that this facilitation is not mediated by GABA_A-dependent intracortical mechanisms, and may instead reflect modulation arising from spinal and interlimb locomotor circuitry. The lack of sustained post-exercise effects indicates that low-intensity arm cycling does not induce a plasticity-permissive cortical state, highlighting a distinction between transient, movement-dependent facilitation and longer-lasting exercise-induced neuroplasticity.