Influence of Aerobic Exercise Intensity on Acute Changes in Motor Activation Post-Stroke

Abstract

Based on evidence among healthy adults, it has been proposed that aerobic exercise (AEX) could acutely activate the brain in ways that facilitate motor learning post-stroke. However, the acute effects of AEX on cortical motor activation have not been well described, and no previous studies have assessed the influence of aerobic intensity on this response among persons with stroke. PURPOSE: To investigate the effect of AEX intensity on acute cortical motor activation among persons with chronic hemiparetic stroke. METHODS: Using a crossover design, 10 subjects (5 male; mean ± SD age, 60.1 ± 8.1 years; 6.1 ± 4.3 years post stroke; comfortable walking speed, 0.69 m/s [52 ± 25% normal]; VO2peak, 16.6 ± 3.4 mL/kg/min [67 ± 14% normal]) performed one 20 minute session of moderate-intensity treadmill AEX (peak speed, 0.69 ± 0.30 m/s; mean VO2, 55 ± 14% VO2peak; blood lactate at end of session, 1.5 ± 0.5 mmol/L) and one 20 minute session of high-intensity treadmill AEX (1.29 ± 0.41 m/s; 62 ± 15% VO2peak; 5.7 ± 3.2 mmol/L) in random order, at least one week apart. High-intensity AEX used an interval training strategy involving 30 second bursts at maximum safe treadmill speed alternated with 30-60 second rest periods. Cortical motor activation threshold of the paretic quadriceps femoris was measured immediately before and after each AEX session using transcranial magnetic stimulation. A fixed effects model to incorporate the crossover design was used to examine between-protocol differences in change. RESULTS: During moderate-intensity AEX, motor threshold increased from 78.2 ± 2.2 to 81.4 ± 2.2% maximum stimulator output (MSO), indicating decreased paretic motor activation. During high-intensity AEX, motor threshold decreased from 80.6 ± 2.2 to 77.3 ± 2.2 % MSO, indicating increased paretic motor activation. The between protocol difference was statistically significant (p=0.037). CONCLUSIONS: In chronic stroke, high-intensity AEX (above the lactate threshold) appears to acutely increase paretic motor activation significantly more than moderate-intensity AEX (below the lactate threshold), which may have the opposite effect. Further studies are needed to confirm this finding in a larger sample and to determine whether this acute motor activation from high-intensity AEX can be used to improve motor outcomes following stroke.