LACTATE AND EPINEPHRINE DURING EXERCISE IN ALTITUDE NATIVES

We tested the hypothesis that the reported low blood lactate accumulat ion ([La]) during exercise in altitude-native humans is refractory to hypoxia-normoxia transitions by investigating whether acute changes in inspired O-2 fraction (FIO2) affect the [La] vs. power output (W) rel ationship or, alternatively, as reported for lowlanders, whether chang es in [La] vs. W on changes in FIO2 are related to changes in blood ep inephrine concentration ([Epi]). Altitude natives [n = 8, age 24 +/- 1 (SE) yr, body mass 62 +/- 3 kg, height 167 +/- 2 cm] in La Pat, Boliv ia (3,600 m) performed incremental exercise with two legs and one leg in chronic hypoxia and acute normoxia (AN). Submaximal one- and two-le g O-2 uptake (VO2) vs. W relationships were not altered by FIO2. AN in creased two-leg peak VO2 by 10% and peak W by 7%. AN paradoxically dec reased one-leg peak VO2 by 7%, whereas peak W remained the same. The [ La] vs. W relationships were similar to those reported in unacclimatiz ed lowlanders. There was a shift to the right on AN, and maximum [La] was reduced by 7 and 8% for one- and two-leg exercises, respectively [ Epi] and [La] were tightly related (mean r = 0.81) independently of FI O2. Thus normoxia attenuated the increment in both [La] and [Epi] as a function of W, whereas the correlation between [La] and [Epi] was una ffected. These data suggest loose linkage of glycolysis to oxidative p hosphorylation under influence from [Epi]. In conclusion, high-altitud e natives appear to be not fundamentally different from lowlanders wit h regard to the effect of acute changes in FIO2 on [La] during exercis e.