Training-dependent changes of red cell density and erythrocytic oxygen transport.

Prolonged endurance training causes a decreased O2 affinity of Hb, which is due to an increase in erythrocyte 2,3-diphosphoglycerate (2,3-DPG) concentration. Possible mechanisms were studied in 20 males with varying degrees of fitness. Training status was tested by ergometry. Red cell density and O2 transport parameters were determined before this test. The O2 tension at 50% O2 saturation of Hb (P50) was higher in the more fit subjects (+1.3 mmHg) and the 2,3-DPG concentration was higher (+2.3 mumol/g Hb) in this group. The mean density was significantly lower in fit subjects (1.1002 g/ml) as compared with less fit subjects (1.1056 g/ml), indicating a lower mean age. Density distribution curves show that in the fit subjects more young erythrocytes were in blood and that the very old erythrocytes were missing. After correction for the differences in the density distribution, no differences in the P50 value and 2,3-DPG concentration between less fit and fit subjects were found. Therefore, the decreased Hb-O2 affinity after training can be explained by the presence of more young erythrocytes in the blood of trained subjects. The magnitude of this effect correlates with the training status.