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

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).

Training intensity‐dependent increases in corticospinal but not intracortical excitability after acute strength training

“…In fact, chronic ST tends to decrease short‐interval intracortical inhibition (SICI) and silent period (SP) duration, suggesting that a release of intracortical inhibition could be one mechanism underlying the chronic increases in cM1 excitability and in the effectiveness of the motor command to increase MVC force. However, the time course of such adaptations is unclear because results from acute studies are inconsistent . In addition to reductions in SICI or SP, an increase in intracortical facilitation (ICF) could also contribute to the increase in CSE.…”

“…ICF is thought to involve corticocortical pyramidal cells with glutaminergic synapses projecting to the cortical neurons that activate the corticospinal tract . However, little is known about changes in ICF after an acute session of ST, with two studies showing little or no changes …”

“…However, the time course of such adaptations is unclear because results from acute studies are inconsistent. 7,[13][14][15] In addition to reductions in SICI or SP, an increase in intracortical facilitation (ICF) could also contribute to the increase in CSE. ICF is thought to involve corticocortical pyramidal cells with glutaminergic synapses projecting to the cortical neurons that activate the corticospinal tract.…”

“…16 However, little is known about changes in ICF after an acute session of ST, with two studies showing little or no changes. 13,15 Therefore, because spinal mechanisms cannot fully account for the changes in CSE in relation to the ST intensity, 6 changes in intracortical circuits could be the main mechanisms modulating CSE. Indeed, contrary to what happens with CSE, which increases with contraction intensity (up to a limit), SICI tends to decrease with the intensity of the voluntary drive.…”

Priming for Improved Hand Strength in Persons with Chronic Tetraplegia: A Comparison of Priming-Augmented Functional Task Practice, Priming Alone, and Conventional Exercise Training

“…This may suggest that changes in CSE are similar for skill training and strength training (26). Conversely, other studies have suggested that resistance training is associated with a decrease in the size of motor-evoked potentials (MEPs) (33, 34), however, the conclusions may depend on the timing of the CSE testing relative to the end of training (34). In persons with tetraplegia, there are surprisingly few studies of progressive resistance training (without concurrent functional electrical stimulation) directed at improving strength in the paretic muscles.…”