Effects of acute isometric resistance exercise on cervicomedullary motor evoked potentials

Abstract

Cervicomedullary motor evoked potentials (CMEPs) in relaxed biceps brachii have been reported to facilitate after acute isometric exercise of the elbow flexors. This facilitation, which reflects either enhanced corticospinal transmission or increased motoneurone excitability, has only been documented in the limb posture used during exercise. In Experiment 1, we tested if these spinal changes "transfer" to a second posture. Fourteen individuals completed 12 sets of high-force isometric contractions of the elbow flexors with the forearm pronated. Before and after exercise, biceps CMEPs were acquired with the forearm either pronated or supinated. CMEPs in pronation and supination were facilitated after exercise, indicating transfer (57.5 ± 55.5% and 53.9 ± 54.9%, respectively; mean ± SD). In Experiment 2, we examined if exercise posture influences the effect that exercise has on CMEPs. A different sample of 14 individuals performed isometric exercise in 2 sessions. In one, exercise was performed in supination. In the other, exercise was performed in pronation. Exercise intensity and volume were the same as in Experiment 1, as were participant characteristics. CMEPs were unchanged after exercise in supination (13.6 ± 31.2%) and pronation (7.7 ± 41.5%). The absence of an effect differs from the finding of Experiment 1. Thus, effects of acute isometric resistance exercise on corticospinal transmission and/or motoneurone excitability are not as consistent as previously thought. When exercise induces this spinal change, the effect is not specific to the posture used for exercise. However, the change does not always occur, and the reasons for this remain unknown.

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

“…Previous studies showed that ST intensity affected CSE but not spinal excitability measured by cervicomedullary electrical stimulation . Furthermore, increases in corticospinal transmission and/or α‐motoneuron excitability after acute ST are not always present . For that reason, mechanisms other than spinal changes were proposed to explain the increases in CSE after acute ST. Increases in corticospinal neuron excitability or reductions in the efficacy of the intracortical inhibitory circuits can both increase the efficacy of the excitatory input to α‐motoneurons thereby increasing the response to TMS.…”

“…6 Furthermore, increases in corticospinal transmission and/or α-motoneuron excitability after acute ST are not always present. 26 For that reason, mechanisms other than spinal changes were proposed to explain the increases in CSE after acute ST. Increases in corticospinal neuron excitability or reductions in the efficacy of the intracortical inhibitory circuits can both increase the efficacy of the excitatory input to α-motoneurons thereby increasing the response to TMS. However, we found no reductions in GABAa or GABAb receptor-mediated cortical inhibition.…”

Effects of Remote Ischemic Conditioning on Hand Engagement in individuals with Spinal cord Injury (RICHES): protocol for a pilot crossover study

“…Several studies have demonstrated transient increased MEPs as an immediate result of post-exercise facilitation in ablebodied participants after a short period of repetitive contraction exercise in thenar 57 , wrist 58 , forearm 59 , or leg muscles 60,61 .…”

Effects of Remote Ischemic Conditioning on Hand Engagement in individuals with Spinal cord Injury (RICHES): protocol for a pilot crossover study

“…Participants will be asked again at the first minute of the following deflation period to check if the pain, discomfort, or other symptoms persist. Several studies have demonstrated transient increased MEPs as an immediate result of post-exercise facilitation in able-bodied participants after a short period of repetitive contraction exercise in thenar 58 , wrist 59 , forearm 60 , or leg muscles 61,62 .…”