Normalizing Cardiorespiratory Fitness To Fat-free Mass Improves Mortality Risk Prediction In Overweight Adults From The Ball St Cohort

Abstract

PURPOSE: Cardiorespiratory fitness(CRF) is a significant predictor of mortality outcomes in various populations, including overweight and obese adults. However, CRF is commonly expressed normalized to total body weight (VO2peakTBW) which may weaken the relationship in obese adults as fat-free mass (FFM) is directly related to CRF, and increased body fat is associated with lower CRF in adults. Therefore, this study aimed to assess the relationship between CRF normalized for FFM(VO2peakFFM) and all-cause mortality, as well as compare the predictive ability of VO2peakFFM and VO2peakTBW in a cohort of self-referred overweight and obese adults. METHODS: Participants included 1,021 overweight and obese adults (520 men, 501 women; BMI: 30.8 ±5.3) who completed a cardiopulmonary exercise test (CPX) and body composition assessment between 1970-2016 to determine CRF. Participants were included if their BMI >25 kg·m-2 and/or waist circumference was >88 cm in women and >102 cm in men. FFM was estimated using the skinfold method to estimate FFM. Participants were followed for 17.8 ± 10.8 years after their CPX and body composition assessments for mortality outcomes. Cox-proportional hazard models were performed to determine the relationship of VO2peakFFM with mortality outcomes. A Wald Chi-square test of equality was performed to compare the predictive ability of CRF expressed as VO2peakTBW and VO2peakFFM. RESULTS: Overall, VO2peakFFM was inversely related to all-cause mortality, with an 11.8% lower risk per 1 ml·kgFFM-1·min-1 improvement, respectively (p<0.01). VO2peakFFM was shown to be a significantly stronger predictor of all-cause mortality than VO2peakTBW (parameter estimates: -0.44 vs. -0.18, p<0.05 respectively). CONCLUSIONS: Body composition is an important factor when considering the relationship between CRF and mortality risk. Clinicians should consider normalizing CRF to FFM when feasible, especially in individuals with excess body fat as it will strengthen the predictive power of the measure.