Association Between the Oxygen Cost of Breathing and Body Composition Among Young Adults With and Without Obesity

Background: The respiratory muscles require ~15% of the total oxygen uptake ([Formula: see text]O 2 ) during vigorous exercise. A high oxygen cost of breathing (O 2cost ) may be a component of exercise intolerance because of increased demand for blood flow and oxygen to respiratory muscles at the expense of other active skeletal muscles (e.g., quadriceps during cycling). Limited evidence in adults with obesity shows higher O 2cost related to higher body mass index (BMI). However, the relation between comprehensive body composition metrics with O 2cost is less clear. Purpose: Our purpose was to determine the association between body fat percentage and related metrics with O 2cost . We tested the hypothesis that a higher body fat percentage in younger adults free of overt disease would be associated with higher O 2cost . Methods: We enrolled adults (20-39 years old) with a BMI <40 kg/m 2 and no cardiometabolic or pulmonary diseases, uncontrolled hypertension, or recent nicotine use. We determined the O 2cost by calculating the slope of [Formula: see text]O 2 , measured via indirect calorimetry, during a 5-minute resting baseline and the final 4 minutes of 8-minute eucapnic voluntary hyperpnea stages performed at 40 and 60 L/min. Respiratory rate was maintained at 20 breaths per minute with a 1:1 duty cycle. We measured anthropometrics and assessed body composition via dual X-ray absorptiometry (DXA). We employed Spearman's rank partial correlations (ρ) and present data as median [IQR]. Results: The participant (n=26) characteristics were: 24[6] years old; 42% female; 8% Asian, 15% Black, 77% White; 31% Latinx; 4.10[1.06] L forced vital capacity (FVC). All calculated O 2cost slopes between stages had R 2 >0.99. The O 2cost (6.28[1.78] mL O 2 /L) was not correlated with BMI (28.4[9.5] kg/m 2 ; ρ<0.01, P=0.98). The O 2cost was also not correlated with DXA body fat percentage (25.9[21.1]%; ρ=-0.06, P=0.79) or visceral adipose tissue mass (433[571] g; ρ=-0.10, P=0.67). Additionally, the O 2cost was not correlated with waist circumference (88.0[24.6] cm; ρ=0.02, P=0.94) or waist-to-hip ratio (0.83[0.06]; ρ=0.19, P=0.34). Moreover, no meaningful correlations existed between O 2cost and any body composition metric after statistically adjusting for age, sex, race, and ethnicity (ρ≤|0.22|, P≥0.27). Interestingly, when FVC was added to this model, we found a moderate positive correlation between the O 2cost and waist-to-hip ratio (ρ=0.48, P=0.03), but no significant correlations were observed with other metrics (ρ≤|0.24|, P≥0.30). Conclusion: These preliminary data suggest that the oxygen cost of breathing is moderately associated with waist-to-hip ratio when FVC is included alongside other traditional covariates (e.g., sex, race, and ethnicity) in young adults with and without obesity, who are free from overt disease. Future studies with larger cohorts are needed to determine the potential role of FVC in mediating the association between waist-to-hip and O 2cost among young adults. Florida State University Graduate School Legacy Fellowship (CD), National Institutes of Health K01HL160772 (JCW), and American Heart Association 23CDA1037938 (JCW). This abstract was presented at the American Physiology Summit 2025 and is only available in HTML format. There is no downloadable file or PDF version. The Physiology editorial board was not involved in the peer review process.