Cortical adaptation following motor fatigue: Dynamic changes in primary motor cortex excitability in healthy young adults.

OBJECTIVE: Motor fatigue induces task-specific behavioral and corticospinal changes, but its post-task after-effects remain poorly understood. We investigated whether sustained repetitive finger tapping (FT) elicits time-dependent modulation of corticospinal excitability in healthy young adults and whether these changes relate to the degree of motor performance deterioration. METHODS: Twenty healthy young participants performed 10 consecutive FT blocks followed by a recovery trial at the final post-task assessment. Motor performance was quantified by kinematic analysis of movement amplitude, velocity, movement rhythm, and intra-trial performance decay. Transcranial magnetic stimulation was performed at baseline and up to 60 min after task completion to assess resting motor threshold (RMT), single-pulse motor evoked potentials (SP-MEPs), short-interval intracortical inhibition (SICI; 2-ms interstimulus interval), intracortical facilitation (ICF; 10-ms interstimulus interval), cortical silent period (CSP), and F-wave measures. RESULTS: FT induced reductions in movement amplitude and velocity, with a significant increase in intra-trial velocity decrement followed by behavioral recovery. Corticospinal excitability increased after FT, as reflected by reduced RMT and enhanced SP-MEP amplitudes, before returning toward baseline. No significant changes were observed in SICI, ICF, CSP, or F-wave measures. The degree of intra-trial velocity decrement correlated with post-task SP-MEP enhancement, indicating that corticospinal modulation scaled with motor performance deterioration. CONCLUSIONS: Sustained repetitive FT induces a reversible and state-dependent modulation of corticospinal excitability following physiological motor fatigue. SIGNIFICANCE: This study characterizes the temporal profile of post-task corticospinal adaptation following physiological motor fatigue and provides a translational framework for investigating altered compensatory responses in neurological disorders.