CARDIOVASCULAR-RESPONSES TO EXERCISE IN SPRINTERS AND DISTANCE RUNNERS

The purpose of this study was to examine the cardiovascular responses of sprinters and distance runners to isometric (IE) and dynamic exercise (DE). Normotensive males were selected and grouped according to prior running performance: sprinter (N = 6) or distance runner (N = 6). Each subject completed an incremental DE (cycle ergometry) test (6-min stages) at 20%, 40%, and 60% of V over dot O-2peak, and 3 min of isometric handgrip at 30% of MVC. Blood pressure (BP), heart rate (HR), cardiac output (Q over dot), oxygen uptake, and blood lactate were measured, while mean arterial blood pressure (MABP), cardiac index (CI), and systemic vascular resistance (SVR) were calculated during each stage of DE. BP and HR were measured during each minute of IE. Muscle biopsies of the vastus lateralis revealed a significant difference in capillary density (capillaries per mm(2) and capillaries per fiber) between the sprinters and distance runners (323 +/- 23 vs 409 +/- 27 and 2.2 +/- 0.2 vs 3.2 +/- 0.3, P < 0.05) and for the percentage of Type I fibers (46.4 +/- 4% vs 64.8 +/- 7%, P < 0.05). The if challenge elicited a greater BP response at minute 3 in the sprinters, which was associated with a greater HR response. During DE, there were no significant differences in BP or HR between the groups. However, at 60% of V O over dot (2peak), the distance runners had a significantly higher cardiac index and a lower systemic vascular resistance than the sprinters (P < 0.05). These results suggest that fiber type and/or alterations in microvessel density induced by training may influence the hemodynamic responses to exercise, even when intensity is normalized to a subject)'s peak aerobic power.