Increases in Heart Rate and RPE Are Additive During Prolonged Exercise in Heat and Hypoxia

To investigate the effects of a combined heat and hypoxic environment on HR and RPE during prolonged exercise. Twelve subjects completed 1 h trials of moderate-intensity exercise on a treadmill while exposed to four different environmental conditions: (1) 23[degrees]C, 20.9% O2, (2) 35[degrees]C, 20.9% O2, (3) 23[degrees]C, 16.5% O2, and (4) 35[degrees]C, 16.5% O2. HR, RPE, core temperature, and arterial oxygen saturation were measured every 5 minutes during the trials. The mean+ or -SD end-exercise HR was 108+ or -10, 125+ or -19, 116+ or -13, and 133+ or -17 bpm for the four conditions. Thus, compared with the control condition (23[degrees]C, 20.9% O2) heat alone increased HR 17 bpm, hypoxia alone increased HR 8 bpm, while heat+hypoxia increased HR 25 bpm. Likewise, end-exercise RPE was 9.8+ or -1.5, 10.8+ or -2.0, 10.4+ or -1.6, and 11.6+ or -2.1 for the four conditions, respectively. Thus, compared with the control condition, heat alone increased RPE 1.0 units, hypoxia alone increased RPE 0.6 units, while heat+hypoxia increased RPE 1.8 units.