Perceived exertion and dyspnea while cycling during a hypoxic and hyperoxic placebo

Rating of perceived exertion (RPE) is used to subjectively quantify the perception of physical activity, breathlessness or dyspnea, and leg discomfort (RPE_legs) during exercise. However, it is unknown how dyspnea or RPE_legs can be influenced by expectations. Thirty healthy, active participants (19 males, 11 females) completed five, 5-minute submaximal cycling trials at 60% peak work rate. We deceived participants by telling them they were inspiring different hypoxic and hyperoxic gases, when in fact they breathed room air. Cardiorespiratory variables were similar between the trials, however, dyspnea and RPE_legs evaluated with a Borg scale changed in a dose-response manner. When participants believed they were breathing 15% O₂, they significantly increased dyspnea +0.70 ± 0.2 units (p = 0.03) compared to room air, whereas RPE_legs was unchanged +0.35 ± 0.1 units (p = 0.70). When participants believed they were breathing 15% O₂, they significantly increased dyspnea +1.05 ± 0.4 units (p = 0.003) compared to 23% hyperoxic condition, whereas RPE_legs was unchanged +0.35 ± 0.1 units (p = 0.70). We found that dyspnea during exercise is susceptible to expectancy, without any accompanying physiological changes. Given coaches and clinicians use perceived exertion to prescribe exercise intensity and evaluate treatments, our findings show that the effect of expectations must be considered when interpreting sensations of breathlessness.