title: Tracking of physical fitness during adolescence: a panel study in boys.
abstract: OBJECTIVE
  To investigate the tracking in physical fitness (PF) viewed as a whole, a multidimensional trait of the subject, and to establish the stability of each factor of PF in adolescence from the perspective of a panel study using the structural equation modeling approach.
  
  
  METHODS
  From a sample of 454 boys followed from 12 to 18 yr of age of the Leuven Growth Study, we considered only three consecutive measurement occasions with a mean age of 12.76, 14.69, and 17.73 yr. Physical fitness was evaluated by means of a battery composed of the following tests: plate tapping, sit and reach, vertical jump, arm pull, leg lifts, bent arm hang, and shuttle run. Structural equation models were fitted to the data, namely autoregressive models with latent variables. These models were used to quantify the tracking of PF as a whole and also of the individual marker variables of fitness.
  
  
  RESULTS
  Stability estimates of PF as a whole are rather high, beta21 = 0.86 and beta32 = 0.68, with an explained variance of 74% and 73%, respectively. Tracking coefficients represented by disattenuated autocorrelations among the fitness factor gave high results: r1,2 = 0.86; r1,3 = 0.78; and r2,3 = 0.85.
  
  
  CONCLUSIONS
  Physical fitness as a whole is highly stable in adolescent years and very predictable from early years. The same is observed for each factor of fitness. Moreover, autoregressive models within the context of structural equation modeling are better suited than simple Pearson or Spearman autocorrelations to study the tracking problem of PF.
authors.affiliation: Faculty of Sport Sciences and Physical Education, University of Porto, Porto, Portugal. jmaia@fcdef.up.pt
authors.forename: J A
authors.initials: JA
authors.lastname: Maia
authors.forename: J
authors.initials: J
authors.lastname: Lefevre
authors.forename: A
authors.initials: A
authors.lastname: Claessens
authors.forename: R
authors.initials: R
authors.lastname: Renson
authors.forename: B
authors.initials: B
authors.lastname: Vanreusel
authors.forename: G
authors.initials: G
authors.lastname: Beunen
mesh_terms: D000293:Adolescent; D000294:Adolescent Behavior; D002648:Child; D002657:Child Development; D015444:Exercise; D005544:Forecasting; D006801:Humans; D008137:Longitudinal Studies; D008297:Male; D008962:Models, Theoretical; D010809:Physical Fitness