Blood O2 affinity and maximal O2 consumption in elite bicycle racers

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Abstract
The PO2 at which Hb is half-saturated with O2 (P50) at 37.degree. C, PCO2 = 42 Torr, measured pH and 2,3-diphosphoglycerate-to-Hb concentration ratio ([2,3-DPG]/[Hb]) values, Hill''s coefficient (n) at rest and maximal O2 consumption (.ovrhdot.VO2 max) 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 competition (competitive season, CoS). 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 < 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 .ovrhdot.VO2 max increased in the course of training 7 and 9% (P < 0.001), respectively, when expressed in absolute units or per kilogram body weight. The .ovrhdot.VO2 max 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 .ovrhdot.VO2 max cannot be explained with adaptive changes of the OEC. The results differ from previous findings reported in other types of athletes.