BackgroundDespite growing interest in the relationship between exercise and short-term neural plasticity, the effects of exercise on motor cortical (M1) excitability are not well studied. Acute, lower-limb aerobic exercise may potentially modulate M1 excitability in working muscles, but the effects on muscles not involved in the exercise are unknown. Here we examined the excitability changes in an upper limb muscle representation following a single session of lower body aerobic exercise. Investigating the response to exercise in a non-exercised muscle may help to determine the clinical usefulness of lower-body exercise interventions for upper limb neurorehabilitation.MethodsIn this study, transcranial magnetic stimulation was used to assess input–output curves, short-interval intracortical inhibition (SICI), long-interval intracortical inhibition (LICI) and intracortical facilitation (ICF) in the extensor carpi radialis muscle in twelve healthy individuals following a single session of moderate stationary biking. Additionally, we examined whether the presence of a common polymorphism of the brain-derived neurotrophic factor (BDNF) gene would affect the response of these measures to exercise.ResultsWe observed significant increases in ICF and decreases in SICI following exercise. No changes in LICI were detected, and no differences were observed in input–output curves following exercise, or between BDNF groups.ConclusionsThe current results demonstrate that the modulation of intracortical excitability following aerobic exercise is not limited to those muscles involved in the exercise, and that while exercise does not directly modulate the excitability of motor neurons, it may facilitate the induction of experience-dependent plasticity via a decrease in intracortical inhibition and increase in intracortical facilitation. These findings indicate that exercise may create favourable conditions for adaptive plasticity in M1 and may be an effective adjunct to traditional training or rehabilitation methods.

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The effect of aerobic exercise on primary motor cortical excitability is a relevant area of interest for both motor learning and motor rehabilitation. Transient excitability changes that may follow an exercise session are a necessary precursor to more lasting neuroplastic changes. While the number of studies is limited, research suggests that a session of aerobic exercise can create an ideal environment for the early induction of plasticity. Potential mechanisms include the upregulation of neurotransmitter activity, altered cerebral metabolism and cortisol levels, and increases in brain-derived neurotrophic factor. While there is considerable evidence that chronic physical activity positively impacts brain health and function, studies examining cortical excitability changes and motor performance after a single session of exercise are lacking. Further research is required to determine the clinical utility and feasibility of aerobic exercise.

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