Acute Strength Training Increases Responses to Stimulation of Corticospinal Axons

Abstract

Via processes within the spinal cord, one session of strength training of the elbow flexors increases net output from motoneurons projecting to the trained muscles. Likely mechanisms include increased efficacy of corticospinal-motoneuronal synapses or increased motoneuron excitability. However, the rate of force generation during training is not important for inducing these changes. A concomitant increase in motor cortical excitability is likely. These short-term changes may represent initial neural adaptations to strength training.

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

“…It is possible that spinal inhibitory mechanisms contribute to this finding (McNeil et al, 2011a). Further, changes in excitability have commonly been found to occur at sub-cortical spinal levels with acute and early strength training (Aagaard, 2003; Nuzzo et al, 2016). Therefore the acute responses may reflect perturbations at subcortical levels.…”

“…In particular, adaptations to the central nervous system such as an increase in corticospinal excitability and release of short-interval intra-cortical inhibition (SICI) following 2- to 8-week strength training programs have been commonly observed (Deschenes et al, 1994; Kidgell et al, 2010; Latella et al, 2012; Weier et al, 2012; Hendy and Kidgell, 2013). While there is strong evidence to suggest that significant neural adaptations occur following multiple resistance training sessions (Kidgell et al, 2010; Latella et al, 2012), and acute changes in corticospinal excitability with sustained submaximal isometric exercise (Nuzzo et al, 2016), few studies have systematically investigated the acute central and peripheral neural responses associated with a single HST session.…”

Effects of acute isometric resistance exercise on cervicomedullary motor evoked potentials

“…Individuals were eligible to present to the laboratory if they were between the ages of 18 and 60; had no existing neurological impairments; had not suffered any serious head or neck injuries in the past; were not pregnant; and were not taking medications that may alter synaptic plasticity (eg, anti‐depressants). The target sample sizes of 14 were based on a priori calculations, which included the observed effect size from our previous experiment . In previous experiments, samples sizes of ~10 have been adequate to observe statistically significant changes in CMEPs after acute bouts of training …”

“…Participants attended the laboratory for one session. In the session, they performed 12 sets of 8 isometric contractions of the elbow flexors . The forearm was pronated during all sets.…”

“…One approach is to examine evoked responses of the corticospinal pathway after a single bout of exercise. The rationale for this approach is that resistance exercise is a form of motor learning, and as such, evidence of “learning” may appear within a single bout . Previously, we have used this approach and discovered that 12 sets of high‐force isometric contractions of the elbow flexors increase responses to subcortical stimulation of corticospinal axons .…”