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 hypoxan thine can be an index of ATP supply-demand imbalance during exercise. The p resent study determined the effects of hypoxic exercise conditioning on wor k capacity, blood lactate, plasma hypoxanthine and various neurohormonal fa ctors, 2. Blood lactate, plasma hypoxanthine and neurohormonal factors (catecholam ines, renin-angiotensin system activity and natriuretic peptides) were meas ured at rest and after maximal cardiopulmonary exercise testing (at sea lev el) both at pre- and post-hypoxic exercise conditioning in six males (40+/- 2 years). The training protocol consisted of ergometer exercise twice weekl y for 40 min in a hypobaric chamber (61.7-47.2 kPa) for 3 weeks. 3. Pulmonary function and haematological and echocardiographic parameters w ere not altered after hypoxic exercise conditioning. Work rate at peak exer cise (264+/-10 vs 321+/-31 W; P = 0.10) tended to be increased and peak O-2 pulse (15.0+/-1.0 vs 18.4+/-1.4 mL/beat; P < 0.05) increased after exercis e conditioning. The double product during submaximal exercise decreased and systolic blood pressure at peak exercise increased after exercise conditio ning. 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 hypox anthine (43.2+/-5.7 vs 26.4+/-5.0 mu mol/L; P < 0.1) tended to be decreased after exercise conditioning, 4. Hypoxic exercise conditioning tended to increase maximal power output wi th a decrease in exercise blood lactate and a trend towards a decrease in e xercise plasma hypoxanthine, These data suggest that exercise conditioning under simulated altitude may improve ATP supply-demand imbalance during exe rcise with less anaerobiosis, which could contribute to enhanced endurance performance.