Maximal respiratory exchange ratio during treadmill cardiopulmonary exercise testing in adults based on age, sex, and body mass index.
Level 4 - case-series / case-control
Cross-sectional observational study of physiological test data.
PubMed 41108803 · doi:10.1016/j.hrtlng.2025.10.002
What was done
The authors analyzed 1612 treadmill ramp cardiopulmonary exercise tests in adults (893 women; 772 with obesity, mean age 42±13 years, BMI 37±5 kg/m²; 840 without obesity, mean age 39±14 years, BMI 24±2 kg/m²). Tests with operational problems or spirometric/ECG abnormalities were excluded. Participants were stratified by BMI (442 normal weight, 398 overweight, 295 class-1 obesity, 247 class-2 obesity, 230 class-3 obesity) and age (<33, 34-46, >46 years). Multiple regression evaluated determinants of maximal respiratory exchange ratio (RER), and an obesity-specific maximum heart rate equation was derived.
What was found
Age, sex, and BMI significantly determined maximal RER (R² = 0.195). Sub-1.0 maximal RER values were observed, notably in obese and older females. The derived maximum heart rate equation was 195.2 - (0.796 × age in years).
Why it matters
Applying fixed RER thresholds like 1.00 may inappropriately classify valid maximal exercise tests as submaximal in older adults and people with obesity, skewing cardiorespiratory fitness evaluations.
Limits
The regression model explained under 20% of the variance in maximal RER, leaving most variability unexplained. Exact subgroup RER values and independent verification against other maximal criteria (such as VO2 plateaus or blood lactate) were not provided in the abstract. Results from treadmill ramp testing may not apply to cycle ergometer protocols.
Cited by
- supports During high-intensity exercise above the anaerobic threshold, respiratory exchange ratio (RER) values can reach 1.3 to 1.4 because carbon dioxide production exceeds oxygen consumption.