Modulation of intracortical inhibition and excitation in agonist and antagonist muscles following acute strength training

Mason, Joel, Howatson, Glyn, Frazer, Alan J., Frazer, Ashlyn K., Pearce, Alan J., Jaberzadeh, Shapour, Avela, Janne and Kidgell, Dawson J. (2019) Modulation of intracortical inhibition and excitation in agonist and antagonist muscles following acute strength training. European Journal of Applied Physiology, 119 (10). pp. 2185-2199. ISSN 1439-6319

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Abstract

Purpose: Transcranial magnetic stimulation (TMS) usually investigates the corticospinal responses ofthe agonist muscle to strength training, despite the role of the antagonist muscle in strengthdevelopment. We examined the intracortical responses from an agonist and antagonist muscle followinga single session of heavy-loaded strength training (dominant-arm only) to identify the early antagonisticresponses to a single session that may accompany improvements in strength.Methods: Corticospinal and motor-cortical excitability and inhibition was collected from agonist andantagonist muscles prior to and following a single session of heavy-loaded wrist flexor training in 18individuals. Training consisted of 4 sets 6-8 repetitions at 80% of 1-repetition maximum (1-RM).Recruitment curves for corticospinal excitability and inhibition of the right wrist flexor and wristextensor muscles were constructed and assessed by examining the area under the recruitment curve(AURC). Intracortical measures were obtained using paired-pulse TMS.Results: Following a single training session, increases in corticospinal excitability (CSE) were observedin both the agonist and antagonist muscles. This was accompanied by decreases in corticospinalinhibition (CSP) in both muscles. Intracortical inhibition was reduced and intracortical facilitation wasincreased for the agonist muscle only. Intracortical measures in the antagonist muscle remainedunchanged after training.Conclusions: These findings indicate that the corticospinal responses to a single session of strengthtraining are similar between agonist and antagonist muscles, but the intrinsic cortico-cortical circuitryof the antagonist remains unchanged. The corticospinal responses are likely due to increasedinvolvement/co-activation of the antagonist muscle during training as the agonist muscle fatigues.

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