The effect of severe and moderate hypoxia on exercise at a fixed level of perceived exertion

Purpose: The purpose of this study was to determine the primary cues regulating perceived effort and exercise performance using a fixed-RPE protocol in severe and moderate hypoxia. Methods: Eight male participants (26  6 y, 76.3  8.6 kg, 178.5  3.6 cm, 51.4  8.0 mL·kg-1·min-1 V ̇O2max) completed three exercise trials in environmental conditions of severe hypoxia (FIO2 0.114), moderate hypoxia (FIO2 0.152) and normoxia (FIO2 0.202). They were instructed to continually adjust their power output to maintain a perceived effort (RPE) of 16, exercising until power output declined to 80 % of the peak 30-s power output achieved. Results: Exercise time was reduced (severe hypoxia 428  210 s; moderate hypoxia 1044  384 s; normoxia 1550  590 s) according to a reduction in FIO2 (P < 0.05). The rate of oxygen desaturation during the first 3-min of exercise was accelerated in severe hypoxia (-5.3 ± 2.8 %·min-1) relative to moderate hypoxia (-2.5 ± 1.0 %·min-1) and normoxia (-0.7 ± 0.3 %·min-1). Muscle tissue oxygenation did not differ between conditions (P > 0.05). Minute ventilation increased at a faster rate according to a decrease in FIO2 (severe hypoxia 27.6 ± 6.6; moderate hypoxia 21.8 ± 3.9; normoxia 17.3 ± 3.9 L∙min-1). Moderate to strong correlations were identified between breathing frequency (r = -0.718, P < 0.001), blood oxygen saturation (r = 0.611, P = 0.002) and exercise performance. Conclusions: The primary cues for determining perceived effort relate to progressive arterial hypoxemia and increases in ventilation.