title: Developmental changes in energy expenditure and physical activity in children: evidence for a decline in physical activity in girls before puberty.
abstract: OBJECTIVE
  To examine individual changes in energy expenditure and physical activity during prepubertal growth in boys and girls.
  
  
  METHODS
  Total energy expenditure (TEE), resting energy expenditure, physical activity-related energy expenditure, reported physical activity, and fat and fat-free mass were measured three times over 5 years in 11 boys (5.3 +/- 0.9 years at baseline) and 11 girls (5.5 +/- 0.9 years at baseline).
  
  
  RESULTS
  Four-year increases in fat ( approximately 6 kg) and fat-free mass ( approximately 10 kg) and resting energy expenditure ( approximately 200 kcal/day) were similar in boys and girls. In boys, TEE increased at each measurement year, whereas in girls, there was an initial increase from age 5.5 (1365 +/- 330 kcal/day) to age 6.5 (1815 +/- 392 kcal/day); however, by age 9.5, TEE was reduced significantly (1608 +/- 284 kcal/day) with no change in energy intake. The gender difference in TEE changes over time was explained by a 50% reduction in physical activity (kcal/day and hours/week) in girls between the ages of 6.5 and 9.5.
  
  
  CONCLUSIONS
  These data suggest a gender dimorphism in the developmental changes in energy expenditure before adolescence, with a conservation of energy use in girls achieved through a marked reduction in physical activity.
authors.affiliation: Division of Physiology and Metabolism, Department of Nutrition Sciences, and the Obesity Research Center, School of Health Related Professions, University of Alabama at Birmingham, Birmingham, Alabama, USA.
authors.forename: M I
authors.initials: MI
authors.lastname: Goran
authors.forename: B A
authors.initials: BA
authors.lastname: Gower
authors.forename: T R
authors.initials: TR
authors.lastname: Nagy
authors.forename: R K
authors.initials: RK
authors.lastname: Johnson
mesh_terms: D001481:Basal Metabolism; D002648:Child; D002657:Child Development / Q000502:physiology*; D002675:Child, Preschool; D002149:Energy Intake; D004734:Energy Metabolism; D015444:Exercise; D005260:Female; D006801:Humans; D008137:Longitudinal Studies; D008297:Male; D005082:Physical Exertion; D011627:Puberty; D012737:Sex Factors