Effects of hypoxic exercise conditioning on work capacity, lactate, hypoxanthine and hormonal factors in men

1. Hypoxanthine is a purine degradation product and exercise plasma hypoxanthine can be an index of ATP supply-demand imbalance during exercise. The present study determined the effects of hypoxic exercise conditioning on work capacity, blood lactate, plasma hypoxanthine and various neurohormonal factors. 2. Blood lactate, plasma hypoxanthine and neurohormonal factors (catecholamines, renin-angiotensin system activity and natriuretic peptides) were measured at rest and after maximal cardiopulmonary exercise testing (at sea level) both at pre- and post-hypoxic exercise conditioning in six males (40 +/- 2 years). The training protocol consisted of ergometer exercise twice weekly for 40 min in a hypobaric chamber (61.7-47.2 kPa) for 3 weeks. 3. Pulmonary function and haematological and echocardiographic parameters were not altered after hypoxic exercise conditioning. Work rate at peak exercise (264 +/- 10 vs 321 +/- 31 W; P = 0.10) tended to be increased and peak O2 pulse (15.0 +/- 1.0 vs 18.4 +/- 1.4 mL/beat; P < 0.05) increased after exercise conditioning. The double product during submaximal exercise decreased and systolic blood pressure at peak exercise increased after exercise conditioning. Resting and exercise neurohormonal factors were unchanged, except for reduced resting plasma adrenaline levels. Blood lactate at peak exercise (7.4 +/- 0.7 vs 4.8 +/- 0.5 mmol/L; P < 0.05) became lower and peak plasma hypoxanthine (43.2 +/- 5.7 vs 26.4 +/- 5.0 mumol/L; P < 0.1) tended to be decreased after exercise conditioning. 4. Hypoxic exercise conditioning tended to increase maximal power output with a decrease in exercise blood lactate and a trend towards a decrease in exercise plasma hypoxanthine. These data suggest that exercise conditioning under simulated altitude may improve ATP supply-demand imbalance during exercise with less anaerobiosis, which could contribute to enhanced endurance performance.