Modeling developmental changes in strength and aerobic power in children.

The present study examined two contrasting multilevel model structures to describe the developmental (longitudinal) changes in strength and aerobic power in children: 1) an additive polynomial structure and 2) a multiplicative structure with allometric body size components. On the basis of the maximum log-likelihood criterion, the multiplicative "allometric" model was shown to be superior to the additive polynomial model when fitted to the data from two published longitudinal studies and to provide more plausible solutions within and beyond the range of observations. The multilevel regression analysis of study 1 confirmed that aerobic power develops approximately in proportion to body mass, m1/3. The analyses from study 2 identified a significant increase in quadriceps and biceps strength, in proportion to body size, plus an additional contribution from age, centered at about peak height velocity (PHV). The positive "age" term for boys suggested that at PHV the boys were becoming stronger in the quadriceps and biceps in relation to their body size. In contrast, the girls' age term was either negligible (quadriceps) or negative (biceps), indicating that at PHV the girls' strength was developing in proportion to or, in the case of the biceps, was becoming weaker in relation to their body size.