title: Physical activity and health-related fitness in youth: a multivariate analysis.
abstract: OBJECTIVE
  To evaluate the relationship between indicators of physical activity and health-related fitness in youth 9-18 yr.
  
  
  METHODS
  A cross-sectional sample of 356 boys and 284 girls 9-18 yr of age from phase I of the Quebec Family Study was studied. The sample was divided into three age groups by gender, 9-12, 13-15, and 16-18 yr of age. Physical activity variables included two estimates of activity, estimated daily energy expenditure (EE) and estimated moderate-to-vigorous physical activity (MVPA), and one estimate of inactivity, time spent watching television per day (TVTIME). Health-related fitness variables were the sum of six skin folds (SUM), number of sit-ups in 1 min (SITUP), physical work capacity at 150 beats x min(-1) (PWC150), and static strength of the leg (LMS). Partial canonical correlation was used to quantify the relationship between standardized (z-transformed) activity variables and health-related fitness items, controlling for age.
  
  
  RESULTS
  There is a weak to moderate association between physical activity and fitness in youth. The first activity canonical variate is a function of positive loadings for EE and MVPA, with a smaller, negative loading for TVTIME. The first fitness variate generally includes positive loadings for PWC150 and SITUP, with a small negative loading for the SUM and a small positive loading for LMS. The first canonical correlations indicate that the variance shared by the fitness and activity variates ranges from 11 to 21%.
  
  
  CONCLUSIONS
  There is a significant relationship between activity and health-related physical fitness, but a large part of the variability (80-90%) in fitness is not accounted for by physical activity as measured in this study.
authors.affiliation: Institute for the Study of Youth Sports, Michigan State University, East Lansing 48824-1049, USA.
authors.forename: P T
authors.initials: PT
authors.lastname: Katzmarzyk
authors.forename: R M
authors.initials: RM
authors.lastname: Malina
authors.forename: T M
authors.initials: TM
authors.lastname: Song
authors.forename: C
authors.initials: C
authors.lastname: Bouchard
mesh_terms: D000293:Adolescent; D002648:Child; D003430:Cross-Sectional Studies; D004734:Energy Metabolism; D005260:Female; D006801:Humans; D008019:Life Style; D008297:Male; D009043:Motor Activity; D015999:Multivariate Analysis; D010809:Physical Fitness; D011792:Quebec; D012307:Risk Factors; D013690:Television