Racial comparison of hemodynamic responses to dynamic exercise and their relationship to muscle fiber composition

The purpose of this study was to examine the relationship between blood pressure responses to dynamic exercise and muscle fiber composition, and compare hemodynamic mechanisms in a biracial group. 30 normotensive, males (15 black, 15 white) completed a dynamic exercise test at 20%, 40%, and 60% of VO_2peak and a muscle biopsy. Blood pressure (BP), heart rate (HR), cardiac index (CI), and oxygen uptake (VO₂) were measured during dynamic exercise and systemic vascular resistance (SVR) was calculated. Blacks demonstrated greater systolic (p = .01) diastolic (p = .002) and mean arterial blood pressure responses (p = .002) to dynamic exercise. No racial difference was present for HR or CI; however, SVR (p = .02) was higher in the blacks. The percentage of type II fibers was greater in blacks (p = .05) and a significant positive correlation (r = .54, p = .003) was found between the change in mean arterial blood pressure from supine rest to 60% of VO_2peak and the percentage of type II fibers. SVR at 60% of VO_2peak was also positively correlated to the percentage of type II fibers (r = .47, p = .01). The results suggests that racial differences in muscle fiber composition may contribute to the greater blood pressure response and higher SVR values in blacks during dynamic exercise.