Introduction: Perceived exertion (RPE) and physiological indices measured during cardiopulmonary testing gauge exercise intensity. Since oxygen consumption (VO2) absent from a known VO2 max does not provide a relative intensity, we evaluated whether respiratory exchange ratio (RER) alone can estimate RPE across submaximal to maximal effort. Hypothesis: RER can predict RPE across submaximal to maximal exercise. Methods: Seven adults (5 males: 21.6±0.55 years, 77.83±6.7 kg, 181.74±6.3 cm, BMI 24.0±6.2 kg/m 2 ; 2 females: 21±0 years, 63.55±8.3 kg, 167.55±5.6 cm, BMI: 22.6±1.5) completed a maximal effort graded exercise treadmill test. Metabolic data was collected continuously (Vyntus CPX). The discontinuous protocol consisted of six 3-minute exercise stages (2 walking and 4 running) each separated by 1 minute of slow walking. Following the last 3-minute running stage, grade was increased 1% each minute until volitional fatigue. RER and RPE (Borg scale) were recorded during the final 15 seconds of each exercise stage. Linear mixed-effects regression analyzed the association of RPE to RER. RER was centered at 1.0 and scaled per 0.10 to report ΔRPE per +0.10 RER. A piecewise ‘above-threshold’ analysis tested for a different slope at RER≥1.0. Given non-standardized stage increments, the primary model omitted stage. Additionally, a sensitivity model with an ordinal stage covariate was also examined. Significance was set at α=0.05. Results: RER was strongly associated with RPE as each +0.10 higher RER corresponded to +3.05±0.29 RPE units (p<0.001). Expressed directly in RER units, RPE≈−16.46+30.5×RER (slope 95% CI 24.70–36.31). The additional slope above RER=1.0 was not significant (p=0.38), supporting a single linear relation across the RER range of ~0.80–1.20. In a sensitivity model adjusting for an ordinal stage index, the RER slope was unchanged as primary vs stage-adjusted slopes produced a similar RER effect: +3.05 vs +3.0 RPE per +0.10 RER (both p<0.001). Conclusion: In this pilot dataset, RER quantitatively tracked RPE during graded maximal exercise, independent of stage. This model provides a practical mapping of metabolic response to perceived effort which is also useful for verifying whether reported exertion matches physiological strain across submaximal to maximal efforts in real time. These findings warrant confirmation in larger, diverse samples and across standardized exercise protocols to refine precision and clinical utility.
Danser et al. (Tue,) studied this question.