Peak blood lactate and blood lactate vs workload during acclimatization to 5,050 m and in deacclimatization

Peak blood lactate ([La-bl](peak)) and blood lactate concentration ([La-bl]) vs. workload (W over dot) relationships during acclimatization to altitude and in the deacclimatization were evaluated in 10 Caucasian lowlanders at sea level (SL(0)); after similar to 1 wk (Alt(1wk)), 3 wk (Alt(3wk)), and 5 wk (Alt(5wk)) at 5,050 m; and weekly during the first 5 wk after return to sea level (SL(1wk)-SL(5wk)). Incremental bicycle ergometer exercises (30 W added every 4 min up to exhaustion) were performed. At Alt(1wk) and at Alt(5wk), the experiments were repeated in hypobaric normoxia (Alt(1wk)-O-2 and Alt(5wk)-O-2) [La-bl] was determined at rest and during the last similar to 30 s of each W over dot. [La-bl](peak) was taken as the highest [La-bl] during recovery. Acid-base status (pH and concentration of HCO3- in arterialized capillary blood) was determined at rest. Mean [La-bl](peak) values were 11.5 (SL(0)), 8.0 (Alt(1wk)), 6.4 (Alt(3wk)), 6.3 (Alt(5wk)), 8.0 (SL(1wk)), 9.4 (SL(2wk)), 10.8 (SL(3wk)), 11.3 (SL(4wk)), and 11.6 (SL(5wk)) mM. At Alt(1wk)-O-2 and Alt(5wk)-O-2, peak W over dot increased, compared with Alt(1wk) and Alt(5wk), whereas no changes were observed for [La-bl](peak). [La-bl] vs. W over dot was shifted to the left (i.e., higher [La-bl] values were found for the same W over dot) at Alt(1wk) compared with SL(0) and partially shifted back to the right (i.e., lower [La-bl] values were found for the same W over dot) at Alt(3wk) and Alt(5wk). At Alt(1wk)-O-2 and Alt(5wk)-O-2, [La-bl] vs. W over dot values were superimposed on that at SL(0). At SL(1wk)-SL(5wk), [La-bl] vs. W over dot values were shifted to the right compared with that at SL(0). At Alt(1wk), a condition of respiratory alkalosis was found, which was only partially compensated for during acclimatization. At SL(1wk), the acid-base status was back to normal. We conclude that 1) the reduced [La-bl](peak) at altitude is still present for 2-3 wk after return from altitude; is not attributable to reduced peak W over dot nor to hypoxia per se, nor to a reduced buffer capacity; alternatively, it could be related to some central determinants of fatigue. 2) The [La-bl] vs. W over dot leftward shift at altitude was due to hypoxia per se. 3) The factor(s) responsible for the [La-bl] vs. W over dot partial rightward shift during acclimatization could still be effective during the first weeks after return to sea level.