title: Age and gender differences in youth physical activity: does physical maturity matter?
abstract: OBJECTIVE
  To investigate whether observed gender differences in objectively measured physical activity (PA) in children (8-13 yr) are confounded by physical maturity differences.
  
  
  METHODS
  Four hundred and one children (194 boys and 207 girls) volunteered for this study. An Actigraph accelerometer was used to obtain seven consecutive days of minute-by-minute PA data for each participant. Minutes of moderate to vigorous PA per day (MVPA), continuous minutes of MVPA per day (CMVPA), and minutes of vigorous PA per day (VPA) were derived from the accelerometer data. Age at peak height velocity (APHV), an indicator of somatic maturity, was predicted in all individuals. Gender differences in the PA variables were analyzed using a two-way (gender x age) ANOVA.
  
  
  RESULTS
  Levels of PA decreased with increasing chronological age in both genders (P < 0.05). When aligned on chronological age, boys had a higher MVPA at 10-13 yr, a higher CMVPA at 9-12 yr, and a higher VPA at 9-13 yr (P < 0.05). When aligned on biological age, PA declined with increasing maturity (P < 0.05); however, gender differences between biological age groups disappeared.
  
  
  CONCLUSIONS
  The observed age-related decline in adolescent boys and girls PA is antithetical to public health goals; as such, it is an important area of research. To fully understand gender disparities in PA, consideration must be given to the confounding effects of physical maturity.
authors.affiliation: College of Kinesiology, University of Saskatchewan, Saskatoon, Saskatchewan, Canada. lauren.sherar@usask.ca
authors.forename: Lauren B
authors.initials: LB
authors.lastname: Sherar
authors.forename: Dale W
authors.initials: DW
authors.lastname: Esliger
authors.forename: Adam D G
authors.initials: AD
authors.lastname: Baxter-Jones
authors.forename: Mark S
authors.initials: MS
authors.lastname: Tremblay
mesh_terms: D000054:Acceleration; D000293:Adolescent; D000367:Age Factors; D000375:Aging; D002648:Child; D015444:Exercise; D005260:Female; D006801:Humans; D008297:Male; D008991:Monitoring, Physiologic / Q000295:instrumentation; D009864:Ontario; D012737:Sex Factors