Abstract

In 219 recreational male runners, we investigated changes in body mass, total body water, haematocrit, plasma sodium concentration ([Naþ]), and urine specific gravity as well as fluid intake during a 100-km ultra-marathon. The athletes lost 1.9 kg (s=1.4) of body mass, equal to 2.5% (s=1.8) of body mass (P50.001), 0.7 kg (s=1.0) of predicted skeletal muscle mass (P50.001), 0.2 kg (s=1.3) of predicted fat mass (P50.05), and 0.9 L (s=1.6) of predicted total body water (P50.001). Haematocrit decreased (P50.001), urine specific gravity (P50.001), plasma volume (P50.05), and plasma [Naþ] (P50.05) all increased. Change in body mass was related to running speed (r=70.16, P50.05), change in plasma volume was associated with change in plasma [Naþ] (r=70.28, P50.0001), and change in body mass was related to both change in plasma [Naþ] (r=70.36) and change in plasma volume (r=0.31) (P50.0001). The athletes consumed 0.65 L (s=0.27) fluid per hour. Fluid intake was related to both running speed (r=0.42, P50.0001) and change in body mass (r=0.23, P=0.0006), but not post-race plasma [Naþ] or change in plasma [Naþ] (P40.05). In conclusion, faster runners lost more body mass, runners lost more body mass when they drank less fluid, and faster runners drank more fluid than slower runners. Verf.-Referat