EFFECT OF INSPIRED O-2 CONCENTRATION ON LEG LACTATE RELEASE DURING INCREMENTAL EXERCISE

The normal rate of blood lactate accumulation during exercise is incre ased by hypoxia and decreased by hyperoxia. It is not known whether th ese changes are primarily determined by the lactate release in locomot ory muscles or other tissues. Eleven men performed cycle exercise at 2 0, 35, 50, 92, and 100% of maximal power output while breathing 12, 21 , and 100% O-2. Leg lactate release was calculated at each stage of ex ercise as the product of ii moral venous blood flow (thermodilution me thod) and femoral arteriovenous difference in blood lactate concentrat ions. Regression analysis showed that leg lactate release accounted fo r 90% of the variability in mean arterial lactate concentration at 20- 92% maximal power output. This relationship was described by a regress ion line with a slope of 0.28 +/- 0.02 min/l and a y-intercept of 1.06 +/- 0.38 mmol/l (r(2) = 0.90). There was no effect of inspired O-2 co ncentration on this relationship (P > 0.05). We conclude that during c ontinuous incremental exercise to fatigue the effect of Inspired O-2 c oncentration on blood lactate accumulation is principally determined b y the rate of net lactate release in blood vessels of the locomotory m uscles.