| Abstract: | We have recently shown that postmenopausal female distance runners demonstrate elevated levels of blood volume compared with sedentary healthy peers. We also found a strong positive relation between blood volume and maximal oxygen consumption. In young adult males, endurance exercise training increases blood volume when performed in the upright, but not in the supine body position. Based on these observations, we hypothesized that among postmenopausal females, the elevation in blood volume would be absent or attenuated in women who train in the horizontal vs. upright body position, and that the lower blood volume in the former would be associated with lower maximal aerobic capacity. Thus, we measured supine resting plasma and total blood volumes (Evans blue dye) and maximal oxygen consumption in postmenopausal women: 10 sedentary controls, 10 swimmers and 10 runners matched for age (60 ± 2; 59 ± 2; 58 ± 2 years, mean ± SE) and hormone replacement use (5 per group). The swimmers and runners were further matched for training volume (4.5 ± 0.2 vs. 4.8 ± 0.6 h week–1), relative performance (78 ± 5 vs. 75 ± 3% of age-group world record) and fat-free mass (45.5 ± 0.8 vs. 44.9 ± 1.5 kg). Total blood volume and maximal oxygen consumption were highest in the runners (81.2 ± 4; 52.4 ± 3 mL kg–1, respectively) and progressively lower in the swimmers (68.8 ± 3; 44.2 ± 2) and controls (59.2 ± 2; 37.9 ± 2; all P < 0.05). In the pooled population, blood volume was positively related to maximal oxygen consumption (r= 0.72, P < 0.0001). We conclude that in endurance-trained postmenopausal females matched for training volume and competitive performance: (1) blood volume is lower in those who train in the horizontal (swimmers) compared with the upright position (runners); (2) the lower blood volume is associated with a lower maximal aerobic capacity. Nevertheless, blood volume and maximal oxygen consumption are higher in postmenopausal women who train in the horizontal position than in sedentary controls. |
