Cardiorespiratory fitness (CRF) measured by oxygen consumption (VO2) during exercise is an important marker of health. The traditional method of indexing VO2 to total body mass is suboptimal since skeletal muscle mass (SMM), rather than fat and extracellular fluid, is the main contributor to CRF. The traditional estimating equations for peak VO2 in youth do not account for this. Bioelectric impedance analysis (BIA) is a non-invasive method to accurately measure body composition. The objectives of this study were to: 1) examine the relationship of body composition indices and peak VO2 in healthy children, adolescents, and young adults, and 2) derive an optimized estimating equation incorporating BIA and compare its performance to traditional estimating equations.
A retrospective, cross-sectional, single-center study of patients <21 years-old referred for exercise testing who did not have underlying cardiovascular disease. All patients underwent BIA immediately prior to exercise testing. Univariable and multivariable linear regression models were constructed and tested for model performance.
A total of 165 young healthy people (mean age 14 years, 48% male) were studied. There was a strong and linear relationship between peak VO2 and SMM (R2=0.79). The sex difference in SMM explained most variability in CRF between boys and girls. A generalized equation using SMM (peak VO2 = 302 - (23.7 × age) - (50.3 × [female = 1, male = 0]) + (81.8 × SMM)) had superior performance (R2=0.80) compared to estimating equations currently used in clinical practice (R2=0.67).
Skeletal muscle mass is a stronger correlate of CRF than is total body mass in youth and may be a better scaling variable to estimate expected peak VO2.