Sex-Specific Longitudinal Modeling of Short-Term Power in 11- to 18-Year-Olds

PURPOSE: To investigate, longitudinally, short-term power output in relation to sex and concurrent changes in age, body mass, fat-free mass (FFM), and maturity status. METHODS: Multiplicative multilevel modeling which enables the effects of variables to be partitioned concurrently within an allometric framework was used to analyze the peak power (PP) and mean power (MP) of 388 11- to 18-yr-olds. Multilevel models were founded on 763 (405 from boys; 358 from girls) determinations of PP and MP from Wingate anaerobic tests, supported by anthropometric measures and maturity status. RESULTS: In both sexes, PP and MP were significantly (P < 0.001) correlated with age, body mass, and FFM. After controlling for body mass, initial models showed positive effects for age on PP and MP, with negative effects for sex and a sex by age interaction. Sex-specific models showed maturity status to have no additional effect on either PP or MP once age and body mass had been controlled for. Skinfold thicknesses in addition to body mass to provide a surrogate for FFM, yielded a significantly (P < 0.05) better statistical fit in all models compared with those based on either body mass or FFM estimated from youth-specific skinfold equations. Models founded on estimated FFM provided a significantly (P < 0.05) better fit than those based on body mass. CONCLUSIONS: With body mass controlled for boys’ PP and MP are higher than those of girls and sex differences increase with age from 11 to 18 yr. A multilevel modeling approach has showed that in both sexes the most powerful influences on short-term power output are concurrent changes in age and FFM as reflected by the combination of body mass and skinfold thicknesses.