TRANSCRANIAL MAGNETIC STIMULATION INTENSITY AFFECTS EXERCISE-INDUCED CHANGES IN CORTICOMOTONEURONAL EXCITABILITY AND INHIBITION AND VOLUNTARY ACTIVATION

摘要

Transcranial magnetic stimulation (TMS) of the motor cortex during voluntary contractions elicits electro-physiological and mechanical responses in the target muscle. The effect of different TMS intensities on exercise-induced changes in TMS-elicited variables is unknown, impairing data interpretation. This study aimed to investigate TMS intensity effects on maximal voluntary activation (VATMS), motor-evoked potentials (MEPs), and silent periods (SPs) in the quadriceps muscles before, during, and after exhaustive isometric exercise. Eleven subjects performed sets of ten 5-s submaximal isometric quadriceps contractions at 40% of maximal voluntary contraction (MVC) strength until task failure. Three different TMS intensities (I-100, I-75, I-50) eliciting MEPs of 53 +/- 6%, 38 +/- 5% and 25 +/- 3% of maximal compound action potential (M-max) at 20% MVC were used. MEPs and SPs were assessed at both absolute (40% baseline MVC) and relative (50%, 75%, and 100% MVC) force levels. VATMS was assessed with I-100 and I-75. When measured at absolute force level, MEP/M-max increased during exercise at I-50, decreased at I-100 and remained unchanged at I-75. No TMS intensity effect was observed at relative force levels. At both absolute and relative force levels, SPs increased at I-100 and remained stable at I-75 and I-50. VATMS assessed at I-75 tended to be lower than at I-100. TMS intensity affects exercise-induced changes in MEP/Mmax (only when measured at absolute force level), SPs, and VATMS. These results indicate a single TMS intensity assessing maximal voluntary activation and exercise-induced changes in corticomotoneuronal excitability/inhibition may be inappropriate. (C) 2015 IBRO. Published by Elsevier Ltd. All rights reserved.