Evidence of a greater functional sympatholysis in habitually aerobic trained postmenopausal women

Habitual aerobic exercise attenuates elevated vasoconstriction during acute exercise (functional sympatholysis) in older men; however, this effect remains unknown in postmenopausal women (PMW). This study tested the hypothesis that, PMW who participate in habitual aerobic exercise, demonstrate a greater functional sympatholysis compared to their untrained counterparts. Nineteen PMW (untrained, n=9 vs. trained, n=10) performed 5-minutes of steady-state (SS) forearm exercise at relative (10% and 20% of maximum; MVC) and absolute (5 kg) contraction intensities. Lower body negative pressure (LBNP) was used to increase sympathetic vasoconstriction during rest and forearm exercise. Brachial artery diameter and blood velocities (via Doppler ultrasound) determined forearm blood flow (FBF; ml·min^-1). Forearm muscle oxygen consumption (VO_2m; ml·min^-1) and arterio-venous oxygen difference (a-vo_2diff) were estimated during SS-exercise and SS-exercise with LBNP. Forearm vascular conductance (FVC; ml·min^-1·100mmHg^-1) was calculated from FBF and mean arterial pressure (MAP; mmHg). Vasoconstrictor responsiveness was determined as the % change in FVC during LBNP. The reduction in FVC (% change FVC) during LBNP was lower in trained compared to untrained PMW at 10% MVC (-7.3±1.2% vs. -13.0±1.1%; P<0.05), 20% MVC (-4.4±0.8% vs. -8.6±1.4%; P<0.05) and 5kg (-5.3±0.8% vs. -8.9±1.4%; P<0.05) conditions, whereas there were no differences at rest (-32.7±4.4% vs. -33.7±4.0%). Peripheral (FVC, FBF and VO_2m) and the magnitude change in systemic hemodynamics (heart rate and MAP) did not differ between groups during exercise. Collectively, the findings present first evidence suggesting that PMW who participate in aerobic exercise demonstrate a greater functional sympatholysis compared to untrained PMW during mild-to-moderate forearm exercise.

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