Effects of acute hypoxia on the inflection point of muscle oxygenation.

The purpose of this study was to investigate the effects of acute hypoxia on the inflection point of muscle oxygenation (IPMO) using near-infrared spectroscopy during incremental bicycle exercise. Eight male subjects (age: 22 +/- 2 years) performed two ramp incremental bicycle exercise tests until exhaustion under each normoxic and hypoxic (F(I)O(2): 0.12) condition. Pulmonary gas exchange and locomotor muscle oxygenation were continuously measured. IPMO was determined as the attenuated point of muscle deoxygenation. Muscle oxygenation level was significantly lower in hypoxia than normoxia throughout the tests. IPMO was found in both conditions, and V(O)(2) at IPMO was significantly decreased in hypoxia. However the percent rate of V(O)(2peak) between normoxia and hypoxia was not significantly different. These results suggest that IPMO was not associated with absolute exercise intensity, but relative exercise intensity.