Abstract

Aim of this study was to test the hypothesis that changes in exercise intensity dominate the PV response to cycle exercise in the heat independent of the initial plasma volume (PV) and total circulating protein (TCP) content. 2 experimental treatments (counterbalanced) were performed by 9 trained male cyclists in both a euhydrated (EU) and hypohydrated (HP, 24-h fluid restriction) state. Blood volume was measured 30 min prior to each test and subsequent changes in PV were calculated from venous blood using hematocrit and hemoglobin concentration. Following 20 min of seated rest in a warm environment, each subject cycled in a semi-reclining posture for 60 min at 3 successive intensities (60, 120, and 180 W for 20 min each). Fluid restriction reduced body weight by 1.4+-0.3 kg (1.8+-0.4%), PV by 353+-73 ml (8+-2%), TCP by 20+-7 g (7+-2%), and elevated serum osmolality by 6+-2 mOsm/kg (2+-1%). After 20 min of passive heat exposure (prior to exercise) TCP content remained lower in HP (17+-5 g) compared with EU as PV increased in EU (222+-27 ml) but not in HP (122+-35 ml). During exercise, TCP decreased in HP by 14+-3 g, which further increased the difference between EU and HP. However, during exercise the overall loss of PV was similar between EU and HP, respectively. These data support the hypothesis that in trained subjects, despite differences in TCP content between hydration states, hypohydration induced by 24-h fluid restriction does not affect the subsequent rate of PV loss during cycle exercise in a warm environment. Verf.-Referat