title: Physical activity but not energy expenditure is reduced in obese adolescents: a case-control study.
abstract: BACKGROUND
  The influence of physical activity on body weight in children and adolescents is controversial.
  
  
  OBJECTIVE
  The objective was to test the hypothesis that the intensity and duration of physical activity differ between obese and normal-weight adolescents, with no difference in estimated energy expenditure.
  
  
  METHODS
  We compared physical activity in 18 (8 males, 10 females) obese [body mass index (in kg/m(2)) > 30] adolescents (14-19 y) with that in a matched, normal-weight (BMI < 27) control group. Total energy expenditure (TEE) was measured with the doubly labeled water method, and physical activity was measured simultaneously by accelerometry. The physical activity level was determined as the ratio of TEE to the resting metabolic rate (RMR) and activity energy expenditure as 0.9 TEE minus RMR. Accelerometry data included total physical activity (counts x min(-1) x d(-1)), accumulated and continuous duration of activity, and continuous 10-min periods of physical activity of moderate intensity.
  
  
  RESULTS
  There was no significant difference in adjusted (analysis of covariance) TEE, RMR, or AEE between groups. The physical activity level was significantly lower (P < 0.05) in the obese group. No sex x group interaction was observed. Differences in total physical activity (P < 0.001), accumulated time (P < 0.05), continuous time (P < 0.01), and continuous 10-min periods of physical activity of moderate intensity (P < 0.01) were observed between groups.
  
  
  CONCLUSIONS
  Obese adolescents are less physically active than are normal-weight adolescents, but physical activity-related energy expenditure is not significantly different between groups. The data suggest that physical activity is not necessarily equivalent to the energy costs of activity.
authors.affiliation: Unit for Preventive Nutrition, Department of Medical Nutrition/Biosciences, Karolinska Institutet, Stockholm, Sweden. ulf.ekelund@ioh.oru.se
authors.forename: Ulf
authors.initials: U
authors.lastname: Ekelund
authors.forename: Jan
authors.initials: J
authors.lastname: Aman
authors.forename: Agneta
authors.initials: A
authors.lastname: Yngve
authors.forename: Cecilia
authors.initials: C
authors.lastname: Renman
authors.forename: Klaas
authors.initials: K
authors.lastname: Westerterp
authors.forename: Michael
authors.initials: M
authors.lastname: Sjöström
mesh_terms: D000293:Adolescent; D016022:Case-Control Studies; D004734:Energy Metabolism; D005260:Female; D006801:Humans; D008297:Male; D009765:Obesity / Q000378:metabolism* / Q000503:physiopathology*; D005082:Physical Exertion; D012016:Reference Values; D013997:Time Factors