Finger tapping at maximal speed evokes crossover fatigability in the other hand

Crossover fatigability (CF) refers to the phenomenon in which fatigability is observed in the non-exercised homologous muscle. As the debate about the existence of CF and its underlying mechanisms is still ongoing and may be protocol-dependent, our study investigated whether CF can be evoked using fast repetitive movements at maximal speed, which have been shown to induce fatigability on the supraspinal level. These rapidly repeating movements induce motor slowing, an involuntary decrease in movement speed. We evoke fatigability through maximal speed finger tapping with one hand and subsequently assessed fast finger tapping performance of the contralateral hand. In two independent cohorts (n = 16, n = 30), we demonstrated that CF can indeed be induced using a motor slowing paradigm. Our findings show that CF manifests as a reduced initial tapping speed in the other, non-exercised hand and as a reduced "movement reserve." Notably, even a brief 10 s period of maximal speed finger tapping was sufficient to evoke this CF effect. Based on our current results and on previous findings, we suggest that CF evoked by motor slowing is unlikely to emerge peripherally and most likely reflects supraspinal mechanisms.