title: Physical activities in adolescent girls: variability in energy expenditure.
abstract: BACKGROUND
  Understanding interindividual variability of energy expended in common activities is important for determining precise estimates of energy expenditure in surveillance studies and clinical trials. The purpose of this study was to describe the variability in energy expenditure for selected physical activities among adolescent girls.
  
  
  METHODS
  Seventy-four adolescent girls (aged 13 to 14 years) participated in this cross-sectional investigation. Data were collected in 2001 and analyzed in 2004. Energy expenditure was measured by indirect calorimetry for ten activities and during a submaximal cycle ergometer test, which was used to estimate cardiorespiratory fitness. Variability in energy expended for the various activities was expressed by standard deviation, coefficient of variation, and range for three different energy expenditure variables: relative VO2 (milliliters per kilogram per minute), absolute VO2 (liters per minute(-1)), and calculated metabolic rate (kilojoules per minute).
  
  
  RESULTS
  Depending on the expression of energy expenditure, coefficients of variation ranged from a low of 13.2% for climbing stairs to a high of 38.4% for playing a computer game. Some lower-intensity activities were associated with greater variability in energy expenditure. Bicycling showed consistently higher coefficients of variation across expressions of energy expenditure (29.1%, 37.7%, and 33.5% for relative VO2, absolute VO2, and calculated metabolic rate, respectively).
  
  
  CONCLUSIONS
  Energy expenditure for common activities is highly variable in adolescent girls. The coefficient of variation was higher in some activities of lower intensity, regardless of energy expenditure expression. This variance may influence the evaluation of physical activity interventions, particularly with regard to issues such as a prescribed dose of activity and the statistical power to detect change.
authors.affiliation: Department of Exercise Science, Arnold School of Public Health, University of South Carolina, Columbia, South Carolina 29208, USA. kapfeiffer@sc.edu
authors.forename: Karin A
authors.initials: KA
authors.lastname: Pfeiffer
authors.forename: Kathryn H
authors.initials: KH
authors.lastname: Schmitz
authors.forename: Robert G
authors.initials: RG
authors.lastname: McMurray
authors.forename: Margarita S
authors.initials: MS
authors.lastname: Treuth
authors.forename: David M
authors.initials: DM
authors.lastname: Murray
authors.forename: Russell R
authors.initials: RR
authors.lastname: Pate
mesh_terms: D000203:Activities of Daily Living / Q000145:classification*; D000293:Adolescent; D000704:Analysis of Variance; D002153:Calorimetry, Indirect / Q000706:statistics & numerical data; D003430:Cross-Sectional Studies; D004734:Energy Metabolism / Q000502:physiology; D015444:Exercise / Q000502:physiology; D005260:Female; D006306:Health Surveys; D006339:Heart Rate / Q000502:physiology; D006801:Humans; D010100:Oxygen / Q000502:physiology; D010809:Physical Fitness / Q000502:physiology; D012016:Reference Values
chemical_list: D010100:Oxygen