Purpose: This study was designed to determine changes in metabolic and cardiovascular risk factors following normobaric hypoxic exercise training in healthy men.
Methods: Following a randomized baseline maximal exercise test in hypoxia and/or normoxia, 34 physically active subjects were randomly assigned to either a normoxic (N = 14) or a hypoxic (N = 18) training group. Training involved 4 wk of cycling exercise inspiring either a normobaric normoxic (F(IO2) = approximately 20.9%) or a normobaric hypoxic (F(IO2) = approximately 16.0%) gas, respectively, in a double-blind manner. Cycling exercise was performed three times per week for 20-30 min at 70-85% of maximum heart rate determined either in normoxia or hypoxia. Resting plasma concentrations of blood lipids, lipoproteins, total homocysteine, and auscultatory arterial blood pressure responses at rest and in response to submaximal and maximal exercise were measured before and 4 d after physical training.
Results: Total power output during the training period was identical in both normoxic and hypoxic groups. Lean body mass increased by 1.4 +/- 1.5 kg following hypoxic training only (P < 0.001). While dietary composition and nutrient intake did not change during the study, both normoxic and hypoxic training decreased resting plasma concentrations of nonesterified fatty acids, total cholesterol, high density lipoprotein (HDL), and low density lipoprotein (LDL) (P < 0.05 - < 0.001). Apolipoproteins AI and B decreased following normoxic training only (P < or = 0.001). Plasma concentrations of resting total homocysteine decreased by 11% following hypoxic training (P < or = 0.05) and increased by 10% (P < 0.05) following normoxic training. These changes were independent of changes in serum vitamin B12 and red cell folate which remained stable throughout. A decreased lactate concentration during submaximal exercise was observed in response to both normoxic and hypoxic training. Hypoxic training decreased maximal systolic blood pressure by 10 +/- 9 mm Hg (P < 0.001) and the rate pressure product by 14 +/- 23 mm Hg x beats x min(-1)/100 (P < or = 0.001) and increased maximal oxygen uptake by 0.47 +/- 0.77 L x min(-1) (P < 0.05).
Conclusion: Normoxic and hypoxic training was associated with significant improvements in selected risk factors and exercise capacity. The stimulus of intermittent normobaric hypoxia invoked an additive cardioprotective effect which may have important clinical implications.