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

The lower peak lactate accumulation in blood ([La-b](p)) at altitude m ay be associated with a reduced maximal glycolytic flux. Based on cert ain assumptions, the latter can be indirectly evaluated in vivo, durin g short supramaximal exercises, by measuring the maximal rate of lacta te accumulation in blood (Delta[La-b](max)). Delta[La-b](max) was dete rmined 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 increa sing duration (5, 15, 25, 35, 45 s or until exhaustion) on a bicycle e rgometer at loads = 200% of the individual W-max. The latter was previ ously determined in each condition as the greatest work rate that coul d be sustained for 2-4 min during an incremental exercise. Net [La-b] accumulation (Delta[La-b]) was measured after each exercise bout. Delt a[La-b] resulted to be linearly related to exercise duration. The slop es of the individual Delta[La-b] vs. exercise duration lines were take n 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 lo ad was higher at SL1 (10.22 +/- 1.09; (x) over bar +/- SD) than at Alt 1 (5.08 +/- 0.82), Alt2 (8.13 +/- 2.67), and SL2 (8.18 +/- 1.43). Delt a[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 conclu ded 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 pote ntial 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.