The Time-Course of Acute Changes in Corticospinal Excitability, Intra-Cortical Inhibition and Facilitation Following a Single-Session Heavy Strength Training of the Biceps Brachii.

Christopher Latella,Dan VanderWesthuizen,Ashlee M. Hendy,Wei-Peng Teo,Alan J. Pearce

doi:10.3389/fnhum.2016.00607

Abstract

Objective: The current understanding of acute neurophysiological responses to resistance training remains unclear. Therefore, we aimed to compare the time-course of acute corticospinal responses following a single-session heavy strength training (HST) of the biceps brachii (BB) muscle and provide quantifiable evidence based on the super-compensation model in an applied setting.Methods: Fourteen participants completed a counter-balanced, cross-over study that consisted of a single HST session (5 sets × 3 repetition maximum [RM]) of the BB and a control session (CON). Single- and paired-pulse transcranial magnetic stimulation (TMS) was used to measure changes in motor-evoked potential (MEP) amplitude, intra-cortical facilitation (ICF), short-interval intra-cortical inhibition (SICI) and long-interval intra-cortical inhibition (LICI). Additionally, maximal muscle compound wave (MMAX) and maximal voluntary isometric contraction (MVIC) of the BB were taken. All measures were taken at baseline, immediately post and at 10, 20, 30 min and 1, 2, 6, 24, 48 and 72 h post-training.Results: A significant reduction in MEP amplitude was observed immediately post training (P = 0.001), while MVIC (P < 0.001) and MMAX (P = 0.047) were reduced for up to 30 min post-training. An increase in MVIC (p < 0.001) and MMAX (p = 0.047) was observed at 6 h, while an increase in MEP amplitude (p = 0.014) was only observed at 48 and 72 h. No changes in SICI, ICF and LICI were observed.Conclusion: Our results suggest that: (1) acute changes in corticospinal measures returned to baseline in a shorter timeframe than the current super-compensation model (24–48 h) and (2) changes in corticospinal excitability post-HST may be modulated “downstream” of the primary motor cortex (M1).

Highlights

It is well-documented that repeated sessions of heavy strength training (HST) induces lasting adaptations at many levels of the neuromuscular system (Sale, 1988; Aagaard et al, 2002; Carroll et al, 2011) resulting in overall strength gains
One-way analysis of variance (ANOVA) showed a main effect of time for HST (F(10,120) = 10.185, P < 0.001)
Post hoc analyses revealed a significantly lower Maximal Voluntary Isometric Contraction (MVIC) immediately post training compared to baseline (−19.5%, p = 0.001)

Summary

Introduction

It is well-documented that repeated sessions of heavy strength training (HST) induces lasting adaptations at many levels of the neuromuscular system (Sale, 1988; Aagaard et al, 2002; Carroll et al, 2011) resulting in overall strength gains (for review see Zatsiorsky, 2008). Acute corticospinal responses following a singlesession of exercise is thought to reflect central fatigue or acute neuroplastic responses to exercise (Smith et al, 2007; Teo et al, 2012) These studies have commonly showed a reduction in corticospinal excitability, as measured by a decrease in motorevoked potential (MEP) amplitude, and an increase in SICI following maximal and submaximal exercise. Peripheral changes such as a reduction in motorneurone excitability and maximal strength production have been reported (Todd et al, 2003). While these studies provide some insights into the initial corticospinal and peripheral responses to exercise, they only provide a short ‘‘window’’ of observation to the neural responses, mostly only up to 60 min post-exercise, which limits our understanding of the time-course and recovery of neuromuscular system following HST

Methods

Results

Discussion

Conclusion