Effects of acute resistance training modality on corticospinal excitability, intra-cortical and neuromuscular responses

Although neural adaptations from strength training are known to occur, the acute responses associated with heavy-strength (HST) and hypertrophy training (HYT) remain unclear. Therefore, we aimed to compare the acute behaviour of corticospinal responses following a single session of HST vs HYT over a 72-h period. Fourteen participants completed a random counterbalanced, crossover study that consisted of a single HST session [5 sets x 3 repetition maximum (RM)], a HYT session (3 sets x 12 RM) of the leg extensors and a control session (CON). Single- and paired-pulse transcranial magnetic stimulation (TMS) was used to measure changes in motor-evoked potential (MEP) amplitude, corticospinal silent period (CSP), intra-cortical facilitation (ICF), short-interval intra-cortical inhibition (SICI) and long-interval intra-cortical inhibition (LICI). Additionally, maximal muscle compound wave (M (MAX)) of the rectus femoris (RF) and maximal voluntary isometric contraction (MVIC) of the leg extensors were taken. All measures were taken at baseline, immediately post and 2, 6, 24, 48 and 72 h post-training. A significant condition x time interaction was observed for MVIC (P = 0.001), M (MAX) (P = 0.003), MEP amplitude (P < 0.001) and CSP (P = 0.002). No differences were observed between HST and HYT for all neurophysiological measures. No changes in SICI, ICF and LICI were observed compared to baseline. Our results suggest that: (1) the acute behaviour of neurophysiological measures is similar between HST and HYT; and (2) the increase in corticospinal excitability may be a compensatory response to attenuate peripheral fatigue.