Strength training reduces intracortical inhibition

Abstract

Paired-pulse transcranial magnetic stimulation was used to investigate the influence of 4weeks of heavy load squat strength training on corticospinal excitability and short-interval intracortical inhibition (rectus femoris muscle). Participants (n=12) were randomly allocated to a strength training or control group. The strength training group completed 4weeks of heavy load squat strength training. Recruitment curves were constructed to determine values for the slope of the curve, V50 and peak height. Short-interval intracortical inhibition was assessed using a subthreshold (0.7×active motor threshold) conditioning stimulus, followed 3ms later by a supra-threshold (1.2×active motor threshold) test stimulus. All motor evoked responses were taken during 10% of maximal voluntary isometric contraction (MVC) torque and normalized to the maximal M-wave. The strength training group attained 87% increases in 1RM squat strength (P<0.01), significant increases in measures of corticospinal excitability (1.2×Motor threshold: 116%, P=0.016; peak height of recruitment curve=105%, P<0.001), and a 32% reduction in short-interval intracortical inhibition (P<0.01) following the 4-week intervention compared with control. There were no changes in any dependent variable (P>0.05) detected in the control group. Repeated high force voluntary muscle activation in the form of short-term strength training reduces short-interval intracortical inhibition. This is consistent with studies involving skilled/complex tasks or novel movement patterns and acute studies investigating acute voluntary contractions.