Acute Effects of Strength and Skill Training on the Cortical and Spinal Circuits of Contralateral Limb.

Unilateral strength and skill training increase strength and performance in the contralateral untrained limb, a phenomenon known as cross-education. Recent evidence suggests that similar neural mechanisms might be responsible for the increase in strength and skill observed in the untrained hand after unimanual training. The aims of this study were to: investigate whether a single session of unimanual strength and skill (force-tracking) training increased strength and skill in the opposite hand; measure ipsilateral (untrained) brain ( transcranial magnetic stimulation, TMS) and spinal ( the monosynaptic reflex) changes in excitability occurring after training; measure ipsilateral (untrained) pathway-specific changes in neural excitability ( TMS-conditioning of the monosynaptic reflex) occurring after training. Participants ( = 13) completed a session of unimanual strength (ballistic isometric wrist flexions) and skill (force-tracking wrist flexions) training on two separate days. Strength increased after training in the untrained hand ( = 0.025) but not in the trained hand ( = 0.611). Force-tracking performance increased in both the trained ( = 0.007) and untrained ( = 0.010) hand. Corticospinal excitability increased after force-tracking and strength training  = 0.027), while spinal excitability was not affected  = 0.214). TMS-conditioned monosynaptic reflex increased after force-tracking ( = 0.001) but not strength training  = 0.689), suggesting a possible role of polysynaptic pathways in the increase of cortical excitability observed after training. The results suggest that cross-education of strength and skill at the acute stage is supported by increased excitability of the untrained motor cortex. A single session of isometric wrist flexion strength and skill straining increased strength and skill in the untrained limb. The excitability of the untrained motor cortex increased after strength and skill training. TMS-conditioned H-reflexes increased after skill but not strength training in the untrained hand, indicating that polysynaptic pathways in the increase of cortical excitability observed after skill training.