Contraction intensity-dependent variations in the responses to brain and corticospinal tract stimulation after a single session of resistance training in men

Abstract

[Abstract]: The aim of this study was to determine the effects of acute resistance training (RT) intensity on motor-evoked potentials (MEPs) generated by transcranial magnetic brain stimula tion and on cervicomedullary motor-evoked potentials (CMEPs) pro duced by electrical stimulation of the corticospinal tract. In four experimental sessions, 14 healthy young men performed 12 sets of eight isometric contractions of the elbow flexors at 0 (Control ses sion), 25, 50, and 75% of the maximal voluntary contraction (MVC). Before and after each session, MEPs, CMEPs, and the associated twitch forces were recorded at rest. MEPs increased by 39% (P 0.05 versus 25% in the control condition, Effect size (ES) 1.04 and 1.76, respectively) after the 50% session and by 70% (P 0.05 vs. all other conditions, ES 0.91–2.49) after the 75% session. In contrast, CMEPs increased similarly after the 25%, 50%, and 75% sessions with an overall increase of 27% (P 0.05 vs. control condition, ES 1.34). The amplitude of maximal compound muscle action potentials (Mmax) was unchanged during the experiment. The MEP and CMEP-associated twitch forces also increased after RT, but training intensity affected only the increases in MEP twitch forces. The data tentatively suggest that the intensity of muscle contraction used in acute bouts of RT affects cortical excitability.