MAXIMAL RATE OF BLOOD LACTATE ACCUMULATION DURING EXERCISE AT ALTITUDE IN HUMANS

The lower peak lactate accumulation in blood ([La-b](p)) at altitude may be associated with a reduced maximal glycolytic flux. Based on certain assumptions, the latter can be indirectly evaluated in vivo, during short supramaximal exercises, by measuring the maximal rate of lactate accumulation in blood (Delta[La-b](max)). Delta[La-b](max) was determined on six white subjects at sea level (SL1), after similar to 1 wk (Alt1) and 4 wk (Alt2) of a 35-day sojourn at 5,050 m, and 1 wk after return to sea level (SL2). The subjects performed exercises of increasing duration (5, 15, 25, 35, 45 s or until exhaustion) on a bicycle ergometer at loads = 200% of the individual W-max. The latter was previously determined in each condition as the greatest work rate that could be sustained for 2-4 min during an incremental exercise. Net [La-b] accumulation (Delta[La-b]) was measured after each exercise bout. Delta[La-b] resulted to be linearly related to exercise duration. The slopes of the individual Delta[La-b] vs. exercise duration lines were taken as Delta[La-b](max). Exhaustion times were similar to 30-45 s in all conditions. [La-b](p) (in mM) during recovery after the exhaustive load was higher at SL1 (10.22 +/- 1.09; (x) over bar +/- SD) than at Alt1 (5.08 +/- 0.82), Alt2 (8.13 +/- 2.67), and SL2 (8.18 +/- 1.43). Delta[La-b](max) was lower at Alt1 (0.09 +/- 0.02) and at Alt2 (0.17 +/- 0.05) than at SL1 (0.25 +/- 0.05) and SL2 (0.23 +/- 0.06). Both [La-b](p) and Delta[La-b](max) increased during acclimatization. It is concluded that the lower [La-b](p) at altitude was associated with a reduced Delta[La-b](max). In the presence of a presumably normal maximal potential activity of glycolytic enzymes, as described by several authors, the reduced Delta[La-b](max) is indicative of an upstream inhibition of glycolysis at altitude.