Purpose: We aimed to compare three candidate body size index models for the scaling of aerobic fitness (V˙O2peak) in children: whole body mass, total lean body mass, and the lean mass of both legs.
Methods: V˙O2peak and total lean mass of the body and both legs (via dual-energy x-ray absorptiometry) were assessed in 126 girls and 87 boys aged 9–11 yr. We applied nonlinear allometric models of the form V˙O2peak = a×body sizeb, adjusted for biological sex and maturity offset (years from peak height velocity). We assessed goodness of fit using the Akaike information criterion.
Results: The Akaike weights (Akaike differences) were as follows: lean mass of both legs = 0.69 (0), total lean body mass = 0.31 (1.6), and whole body mass = <1e−8 (36.6). The size exponent (90% confidence interval) for the lean mass of both legs was 0.55 (0.46–0.64). V˙O2peak was 17% (13%–21%) lower in girls after controlling for the lean mass of both legs and maturity offset. After controlling for body size and sex, a 1-yr increase in maturity offset (closer to peak height velocity) was associated with a 6% (4%–9%) higher V˙O2peak.
Conclusions: Allometric scaling of V˙O2peak by the lean mass of both legs provides the best model for quantifying growth-related changes in aerobic fitness in pediatric populations, although this model is only marginally superior to the total lean body mass model. There is no support for the total body mass model. Maturity and sex are also important covariates exerting a size-independent influence on peak aerobic fitness.