Influence of Sex and Body Composition on Aerobic Capacity in Normal Weight Lean, Normal Weight Obese, and Obese Phenotypes

Normal weight obesity (NWO) is a body composition phenotype that is associated with increased cardiometabolic risk and is characterized by a normal weight body mass index but elevated body fat. The purpose of this study was to determine sex differences in aerobic capacity across body composition phenotypes, including normal weight lean (NWL), NWO, and traditional obesity (OB). We recruited 60 participants according to three body composition phenotypes: NWL (n = 10 females, n = 10 males), NWO (n = 10 females, n = 10 males), and OB (n = 10 females, n = 10 males). Measurements included fasting metabolic risk factors, body composition X-ray scan, and peak exercise test on a cycle ergometer to determine aerobic capacity (VO 2peak ). Across groups, males (34.5 ± 11.7 mL/kg/min) exhibited greater VO 2peak than females (28.8 ± 8.8 mL/kg/min; p = 0.04). There were no differences in VO 2peak between sexes within the same body composition phenotype, but NWL (42.7 ± 9.0 mL/kg/min) exhibited greater VO 2peak than NWO (27.9 ± 4.4 mL/kg/min; p < 0.0001) and OB (24.4 ± 7.3 mL/kg/min; p < 0.0001). VO 2peak was inversely correlated with relative body fat in the full sample (r = −0.67; p < 0.0001), but was stronger in males ( r = −0.78; p < 0.0001) than females ( r = −0.53; p = 0.0028). Visceral adipose tissue was not significantly correlated with VO 2peak in the full sample ( r = −0.25; p = 0.05) or in males ( r = −0.23; p = 0.25), although they were inversely correlated in females ( r = −0.36; p = 0.048). Our results suggest low aerobic capacity in both men and women with NWO, similar to men and women with OB. The relationship between body composition and aerobic capacity is strong across body composition phenotypes, but appears to be more consistent in females than males. For healthcare professionals aiming to lower cardiometabolic risk, attention should be given to improving aerobic fitness in both men and women with elevated body fat, including those with NWO.