NEURAL EXCITABILITY FOLLOWING RESISTANCE TRAINING STUDIED WITH TRANSCRANIAL MAGNETIC STIMULATION

Abstract

An increase in the excitability of the central nervous system during resistance training has been implicated through observations of increases in the surface EMG during maximal contractions. PURPOSE The purpose of the study was to test this hypothesis by measuring changes in the amplitude of motor evoked potentials (MEP) elicited by transcranial magnetic stimulation of the cortex before and after short-term resistance training. METHODS Ten subjects participated in a resistance training program and 10 subjects were matched as controls. The training group performed six sets of 10 maximal isometric voluntary contractions (MVCs) of the tibialis anterior muscle three times a week for four weeks. Each contraction was held for 5 seconds. The data recorded during the experiment were: the average of three maximal voluntary contractions at the start of each training day, mean maximal surface EMG (EMGmax) during three MVCs, maximal M-waves elicited by supramaximal stimulation of the peroneal nerve and the average of ten MEPs elicited during a baseline contraction of 10% MVC. RESULTS There was a progressive increase in all parameters over the course of the experiment. By the end of the twelfth training session the pooled data showed that the force of the maximal voluntary contraction increased by 18.9 ± 1.8%. The peak-to-peak amplitude of the maximal M-wave, RMS of the maximal surface EMG normalized to the maximal M-wave and the peak-to-peak amplitude of the MEP normalized to the maximal M-wave all increased significantly (p <0.05). There were no changes in any of these parameters measured in the control group over the same period. CONCLUSION These data indicate that there may be an increase in the excitability of the entire motor pathway, from the cortex to the sarcolemma, following a short, intense period of isometric resistance training. However, the extent to which this increase in excitability actually functions to increase maximal force output needs to be determined. Supported by NSERC