Body Composition, Obesity, and Cardiorespiratory Fitness in the Community.

PURPOSE: Cardiorespiratory fitness (CRF) is an integrative measure of physiologic health, but how CRF relates to different body composition components and cardiometabolic health in community-dwelling adults remains uncertain, especially in obesity. METHODS: In Framingham Heart Study (FHS) Generation 3/Omni-2 participants, body composition measures from dual-energy X-ray absorptiometry (DXA) were related to peak oxygen uptake (VO2) and complementary exercise phenotypes assessed via cardiopulmonary exercise testing in sex-stratified multivariable linear models. Secondary analyses examined correlates of peak VO2 when indexed to total body weight or lean mass. RESULTS: Among 2647 participants (53% women, mean age 54 years, body mass index [BMI] 27.8 kg/m 2), lean mass was the strongest correlate of CRF among body composition measures (FDR <5%) and, along with age and height, accounted for 44-48% of the variance in peak VO2. A 1 kg-higher lean mass was associated with a 43 ml/min-higher absolute peak VO2. While there was broad consistency across age, sex-based differences in the relations of body composition and CRF were observed, with women demonstrating stronger positive associations between CRF and fat mass compared to men. Peak VO2 displayed distinct cardiometabolic correlates depending on whether it was indexed to total body weight versus lean mass: "metabolically healthy" obesity displayed lower peak VO2 compared to "metabolically healthy" non-obesity with indexing to total body weight, but peak VO2 was similar between these two categories with indexing to lean mass. CONCLUSIONS: Lean mass is the strongest correlate of CRF in middle-aged, community-dwelling individuals. Indexing peak VO2 to lean versus total mass results in different conclusions regarding the intersections of CRF with obesity and metabolic health and emphasizes the role of cardiometabolic risk factors beyond obesity itself.