Diminished sympathoinhibition during the onset of low-intensity leg cycling in young Black males.

Previous studies have reported that non-Hispanic Black (BL) males exhibit augmented blood pressure (BP) responses to dynamic exercise relative to White males; however, the underlying mechanism(s) remain unclear. To our knowledge, no studies have examined the muscle sympathetic nerve activity (MSNA) response to dynamic exercise in BL adults. The purpose of this study was to examine potential racial differences in the sympathoinhibition that occurs at the onset of dynamic exercise. We hypothesized that cardiopulmonary baroreflex-mediated inhibition of sympathetic vasomotor outflow during the onset of low-intensity dynamic exercise is diminished in BL individuals. MSNA was recorded via microneurography of the left radial nerve in 9 BL (20 ± 3 yr, mean ± SD) and 11 non-Hispanic White (WH; 22 ± 4 yr) males. BP was measured by finger photoplethysmography, which was verified by automated brachial BP measures. Participants performed 3 min of bilateral leg cycling at 15 W on a cycle ergometer in the 70° semirecumbent position. MSNA burst frequency (BF) decreased during cycling in both groups; however, the decrease was significantly smaller (P < 0.001) in the BL group (-4.7 ± 3.7 bursts/min) than in the WH group (-11.3 ± 5.0 bursts/min). Mean BP increased during cycling in both groups, with no significant difference between the two groups (BL +7.4 ± 4.2 vs. WH +6.9 ± 7.1 mmHg, P = 0.958). These findings suggest that cardiopulmonary baroreflex-mediated inhibition of sympathetic vasomotor outflow at the onset of dynamic exercise is diminished in BL males compared to WH males.NEW & NOTEWORTHY It is unknown whether racial differences exist in sympathetic inhibition during the onset of dynamic exercise. We observed that the reduction in muscle sympathetic nerve activity during low-intensity leg cycling was less in young non-Hispanic Black males than in age-matched non-Hispanic White males. These findings suggest that cardiopulmonary baroreflex-mediated inhibition of sympathetic vasomotor outflow during leg cycling may be diminished in Black individuals.