Sex-Specific Longitudinal Modeling of Youth Peak Oxygen Uptake.

To investigate peak oxygen uptake ( ) in relation to sex, age, body mass, fat-free mass (FFM), maturity, and overweight status. Multiplicative, allometric models of 10- to 18-year-olds were founded on 1057 determinations of peak supported by anthropometry and estimates of maturity status. Baseline models with body mass controlled for showed age to exert a positive effect on peak , with negative estimates for age, sex, and a sex-by-age interaction. Sex-specific models showed maturity status to have a positive effect on peak in addition to the effects of age and body mass. Introducing skinfold thicknesses to provide, with body mass, a surrogate for FFM explained maturity effects and yielded a significantly ( < .05) better statistical fit in all models compared with those based on FFM estimated from youth-specific skinfold equations. With girls only, the introduction of overweight, defined by body mass index, resulted in a small but significant ( < .05) negative effect, with an age-by-overweight status interaction. FFM has a powerful influence on peak in both sexes. Interpretation of the development of youth aerobic fitness and its application to health should reflect the sex- and maturity-associated variation in FFM.