INTRODUCTION: After maximal voluntary contractions (MVCs), responses to corticospinal tract stimulation change differently in arm and leg muscles. This study we examined responses in the first dorsal interosseous muscle (FDI). METHODS: Stimulation of the corticospinal tract at the cervicomedullary motor evoked potentials in FDI. Stimuli were delivered before and after 10-s and 1-min MVCs. The reproducibility of changes in the cervicomedullary motor evoked potentials (CMEPs) was investigated. F-waves tested motoneuron excitability. RESULTS: After the MVCs, the CMEP area was initially variable. By ~1 min after 10-s and 1-min MVCs, CMEPs in relaxed muscle decreased to 63 ± 15% and 52 ± 32%, respectively, of control and remained depressed for ~10 min. Responses evoked 2 days apart varied between subjects but not between days. After 10-s MVCs, F-waves were reduced at rest. During weak contraction, CMEPs but not F-waves were depressed. CONCLUSIONS: Our results suggest that contraction produces changes at the corticomotoneuronal synapses to FDI. In addition, motoneuron excitability is reduced.
INTRODUCTION: After maximal voluntary contractions (MVCs), responses to corticospinal tract stimulation change differently in arm and leg muscles. This study we examined responses in the first dorsal interosseous muscle (FDI). METHODS: Stimulation of the corticospinal tract at the cervicomedullary motor evoked potentials in FDI. Stimuli were delivered before and after 10-s and 1-min MVCs. The reproducibility of changes in the cervicomedullary motor evoked potentials (CMEPs) was investigated. F-waves tested motoneuron excitability. RESULTS: After the MVCs, the CMEP area was initially variable. By ~1 min after 10-s and 1-min MVCs, CMEPs in relaxed muscle decreased to 63 ± 15% and 52 ± 32%, respectively, of control and remained depressed for ~10 min. Responses evoked 2 days apart varied between subjects but not between days. After 10-s MVCs, F-waves were reduced at rest. During weak contraction, CMEPs but not F-waves were depressed. CONCLUSIONS: Our results suggest that contraction produces changes at the corticomotoneuronal synapses to FDI. In addition, motoneuron excitability is reduced.