The effects of endurance exercise in hypoxia on acid-base balance and potassium kinetics: a randomized crossover design in male endurance athletes

BACKGROUND: Exercise-induced disturbance of acid-base balance and accumulation of extracellular potassium (K(+)) are suggested to elicit fatigue. Exercise under hypoxic conditions may augment exercise-induced alterations of these two factors compared with exercise under normoxia. In the present study, we investigated acid-base balance and potassium kinetics in response to exercise under moderate hypoxic conditions in endurance athletes. METHODS: Nine trained middle-to-long distance athletes [maximal oxygen uptake (VO(2max)) 57.2 ± 1.0 mL/kg/min] completed two different trials on different days, consisting of exercise in moderate hypoxia [fraction of inspired oxygen (F(i)O(2)) = 14.5%, H trial] and exercise in normoxia (F(i)O(2) = 20.9%, N trial). They performed interval endurance exercise (8 × 4 min pedaling at 80% of VO(2max) alternated with 2-min intervals of active rest at 40% of VO(2max)) under hypoxic or normoxic conditions. Venous blood samples were obtained to determine blood lactate, pH, bicarbonate ion, and K(+) concentrations before exercise, during exercise, and after exercise. RESULTS: The blood lactate concentrations increased significantly with exercise in both trials. Exercise-induced blood lactate elevations were significantly greater in the N trial than in the H trial at all time points (P = 0.012). Bicarbonate ion concentrations (P = 0.001) and blood pH (P = 0.019) during exercise and post-exercise periods were significantly lower in the N trial than in the H trial. A significantly greater exercise-induced elevation in blood K(+) concentration was produced in the N trial than in the H trial during exercise and immediately after exercise (P = 0.03). CONCLUSIONS: High-intensity interval exercise on a cycle ergometer under moderate hypoxic conditions did not elicit a decrease in blood pH or elevation in K(+) levels compared with an equivalent level of exercise under normoxic conditions.