Boys with Obesity have Attenuated Cardiorespiratory Fitness Independent of Fat Mass

Abstract

PURPOSE: The assessment of cardiorespiratory fitness using ratio scaling to total body mass (TBM) is confounded by fat mass in obese populations because fat tissue does not contribute to oxygen utilization during exercise. Our objective was to isolate the independent effects of obesity on fitness when normalized to total lean body mass (TLM) and leg lean mass (LLM). We tested the hypothesis that boys with obesity would have attenuated cardiorespiratory fitness compared to age-matched non-obese boys. METHODS: Values are expressed as means ±SD with significance set at P<0.05. Seventeen non-obese boys (10.6±0.9y, 141.8±6.5cm, 35.5±7.0kg, 24±5% body fat) and thirteen age-matched obese boys (10.6±1.4y, 146.3±10.6cm, 60.25±13.0kg, 44±2% body fat) completed a cardiorespiratory fitness test (VO2peak) and body composition scan (DXA). RESULTS: Utilizing a 2-tailed independent T-test, both groups had comparable VO2peak test times (9.1±1.4 min; P=0.80), and peak heart rates (187±12 bpm; P=0.50). Boys with obesity had a reduction in VO2peak when normalized to TBM (54% of age-matched boys without obesity); however, this effect was reduced less when compared to LBM (76%) and LLM (68%). Further, simple linear regression found that total body fat accounted for 69% variance for mL/kgTBM/min, 49% variance for mL/kgLBM/min, and 40% variance for mL/kgLLM/min. CONCLUSIONS: These data indicate that obesity in young boys impairs cardiovascular fitness which supports the concept that obesity in pediatrics reduces aerobic capacity, which may have later life consequences in regards to cardiorespiratory fitness and all-cause mortality. Lastly, we show that the normalization of VO2 to LBM and LLM can provide an independent measure of fitness.