Effects of sustained unilateral handgrip on corticomotor excitability in both knee extensor muscles

PURPOSE Repetitive or sustained simple muscle contractions have been shown to alter corticomotor excitability. The present study investigated the effects of a sustained handgrip contraction with the right hand on motor-evoked potentials (MEPs) in task-unrelated knee extensor muscles and determined whether the effects are influenced by intensity of the handgrip contraction. METHODS Subjects performed a 120-s sustained handgrip contraction at 10% or 50% maximal voluntary contraction (MVC) using the right hand. MEPs in vastus lateral (VL) muscles elicited by transcranial magnetic stimulation were measured before, during, and after the handgrip contraction. RESULTS Both the handgrip contractions at 10 and 50% MVC induced significant greater MEPs in the left VL muscle (121.5 ± 25.7%) than in the right VL muscle (97.9 ± 17.4%) from 10 min after the handgrip contraction (P < 0.05). MEPs in both the right and left VL muscles were significantly increased by the handgrip contractions at 10% MVC (124.8 ± 45.2%, P < 0.05), but were not increased by the handgrip contractions at 50% MVC. CONCLUSION The results of the present study indicate that a unilateral sustained handgrip contraction can differentially alter corticomotor excitability in knee extensor muscles ipsilateral and contralateral to the exercised hand after the handgrip and that the intensity of the handgrip contraction influences corticomotor excitability in both knee extensor muscles after the handgrip.