Background: Despite growing interest in the relationship between exercise and short-term neural plasticity, the\neffects of exercise on motor cortical (M1) excitability are not well studied. Acute, lower-limb aerobic exercise may\npotentially modulate M1 excitability in working muscles, but the effects on muscles not involved in the exercise are\nunknown. Here we examined the excitability changes in an upper limb muscle representation following a single\nsession of lower body aerobic exercise. Investigating the response to exercise in a non-exercised muscle may help\nto determine the clinical usefulness of lower-body exercise interventions for upper limb neurorehabilitation.\nMethods: In this study, transcranial magnetic stimulation was used to assess inputââ?¬â??output curves, short-interval\nintracortical inhibition (SICI), long-interval intracortical inhibition (LICI) and intracortical facilitation (ICF) in the\nextensor carpi radialis muscle in twelve healthy individuals following a single session of moderate stationary biking.\nAdditionally, we examined whether the presence of a common polymorphism of the brain-derived neurotrophic\nfactor (BDNF) gene would affect the response of these measures to exercise.\nResults: We observed significant increases in ICF and decreases in SICI following exercise. No changes in LICI were\ndetected, and no differences were observed in inputââ?¬â??output curves following exercise, or between BDNF groups.\nConclusions: The current results demonstrate that the modulation of intracortical excitability following aerobic\nexercise is not limited to those muscles involved in the exercise, and that while exercise does not directly modulate\nthe excitability of motor neurons, it may facilitate the induction of experience-dependent plasticity via a decrease in\nintracortical inhibition and increase in intracortical facilitation. These findings indicate that exercise may create\nfavourable conditions for adaptive plasticity in M1 and may be an effective adjunct to traditional training or\nrehabilitation methods.
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