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UBC Theses and Dissertations

Acute lower extremity resistance exercise and the effects on corticospinal excitability in the unexercised upper extremity Attard, Kaitlin


Cross-education (CE) of strength occurs when a muscle is trained unilaterally and bilateral improvements in strength are noted. Unilateral resistance exercise can therefore be advantageous for clinical populations, including individuals with stroke, as a means to improve strength bilaterally when only the less affected side of the body can be trained. Yet we do not understand the mechanism through which CE is mediated in the brain, nor do we know if the cortical effects of CE are localized and spatially confined to homologous muscles. The main purpose of the current thesis was to determine the impact of bilateral and unilateral lower extremity (LE) resistance exercise on corticospinal excitability in the unexercised upper extremity (UE). Twelve healthy participants were recruited to participate in two sessions on separate days. During each session, transcranial magnetic stimulation (TMS) and peripheral nerve stimulation were used to quantify baseline corticospinal excitability in the unexercised UE in the abductor pollicus brevis muscle (APB). This was followed by an acute bout of either a bilateral or unilateral leg extension exercise condition. All participants completed both conditions; the order of the conditions was randomized. Immediately following the acute exercise bout, measures of corticospinal excitability were repeated in the same manner as at baseline. Strength improved in both legs post-exercise in the bilateral (p= 0.042) and unilateral (p=0.005) condition. There was a decrease in intracortical inhibition after bilateral leg extensions were performed in both hemispheres (p=0.05). There were no changes in corticospinal excitability after the unilateral exercise. There were no changes in spinal excitability in either condition in the unexercised UE after LE resistance exercise. These data suggest that unilateral resistance exercise can improve strength bilaterally. In addition, an acute bout of bilateral LE resistance exercise can influence cortical areas beyond the cortical representation of the exercised limbs. However, acute unilateral resistance exercise bouts may not be able to produce these wide-spread cortical changes to the same extent as bilateral exercise. This current research contributes to the current CE literature, helping to explain the limits of this phenomenon which in turn will facilitate the assimilation of CE into clinical practice.

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