This study tested the hypothesis that high cardiorespiratory fitness (VO2max) preserves the cortical circuitry associated with cardiac arousal during exercise in middle to older-aged individuals. Observations of changes in heart rate (HR) and in cortical blood oxygenation level dependent (BOLD) images were made in 52 healthy, active individuals (45-73 years; 16 female) across a range of fitness (26-66mL/kg/min). Seven repeated bouts of isometric handgrip (IHG) at 40% MVC force were performed using functional magnetic resonance imaging at 3-Tesla, with each contraction lasting 20 sec and separated by 40 sec of rest. HR responses to IHG showed high variability across individuals. Linear regression revealed that cardiorespiratory fitness was not a strong predictor of the HR response (r2=0.09). In a region-of-interest analysis both the IHG task and HR time course correlated with increased cortical activation in the bilateral insula and decreased activation relative to baseline in the anterior and posterior cingulate and medial prefrontal cortex (MPFC). T-test results revealed greater deactivation at the MPFC with fitness levels beyond that of guideline based activity. Therefore, whereas high cardiorespiratory fitness failed to affect absolute HR responses to IHG in this age range, a select effect was observed in cortical regions known to be associated with cardiovascular arousal.
- cortical autonomic network
- handgrip exercise
- cardiorespiratory fitness
- medial prefrontal cortex
- Copyright © 2016, Journal of Neurophysiology