Blood O2 affinity and maximal O2 consumption in elite bicycle racers

The PO2 at which hemoglobin is half-saturated with O2 (P50) at 37 degrees C, PCO2 = 42 Torr, measured pH and 2,3-diphosphoglycerate-to-hemoglobin concentration ratio ( [2,3-DPG]/[Hb]) values, Hill's coefficient (n) at rest, and maximal O2 consumption (VO2max) were determined in 11 world-class professional bicycle racers off-season (control, C), after 3 mo of 3 h daily training (preseason, PrS), and after additional 6 mo of competitions (competitive season, CoS). The results indicate that the P50 observed in trained athletes was the same as that of a comparable group of sedentary subjects (Sed) under the same conditions of pH, PCO2, and [2,3-DPG]/[Hb] and was similar to that obtained after "normalization" in respect to pH and the [2,3-DPG]/[Hb]; [2,3-DPG]/[Hb] increased as a function of training from 0.72 to 0.95 (P less than 0.001); the slope of the central portion of the O2 equilibrium curve (OEC) was nearly unaffected by endurance training as indicated by the n value (NCoS = 2.70 +/- 0.08; nSed = 2.65 +/- 0.08); and VO2max increased in the course of training 7 and 9% (P less than 0.001), respectively, when expressed in absolute units or per kilogram body weight. The VO2max predicted on the basis of a computer simulation does not increase significantly as a consequence of the measured rise in [2,3-DPG]. Therefore, the observed increase of VO2max cannot be explained with adaptive changes of the OEC. The present results differ from previous findings reported in other types of athletes.