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

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.

Eight male participants (26 ± 6 years, 76.3 ± 8.6 kg, 178.5 ± 3.6 cm, 51.4 ± 8.0 mL kg^- 1 min^- 1[Formula: see text]O_2max) completed three exercise trials in environmental conditions of severe hypoxia (F_IO₂ 0.114), moderate hypoxia (F_IO₂ 0.152), and normoxia (F_IO₂ 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.

Exercise time was reduced (severe hypoxia 428 ± 210 s; moderate hypoxia 1044 ± 384 s; normoxia 1550 ± 590 s) according to a reduction in F_IO₂ (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 F_IO₂ (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.

The primary cues for determining perceived effort relate to progressive arterial hypoxemia and increases in ventilation.