Abnormal post-exercise depression of corticomotor excitability is associated with fatigue in post-COVID-19 condition.

BACKGROUND: Persistent fatigue is a disabling symptom of post-COVID-19 condition (PCC), but objective neurophysiological markers of post-exertional dysfunction remain poorly defined. Post-exercise depression (PED) of corticomotor excitability, assessed by transcranial magnetic stimulation (TMS), is an index of central fatigability, but its relationship with subjective fatigue in PCC is unclear. METHODS: We studied 58 patients with PCC and 22 age- and sex-matched healthy controls (HCs). Participants performed a 1-min sustained maximal voluntary pinching task. Corticomotor excitability was assessed before and after exercise by motor-evoked potential (MEP) amplitude and cortical silent period (SP) duration recorded from the first dorsal interosseous muscle. Fatigue severity and perceived exertion were assessed using the Fatigue Severity Scale, Fatigue Rating Scale, and Borg CR100 scale. RESULTS: Post-exercise modulation of corticomotor excitability differed between groups. Compared with HCs, PCC patients showed a smaller reduction in MEP amplitude. HCs showed post-exercise SP prolongation, whereas patients showed minimal change or paradoxical shortening. Lower MEP reduction and reduced SP prolongation correlated with higher fatigue and exertion. CONCLUSIONS: PED abnormalities suggest altered regulation of corticomotor output after exertion in PCC. SIGNIFICANCE: PED may provide an objective neurophysiological marker of altered central fatigability.