title: Evaluation of methods to assess physical activity in free-living conditions.
abstract: OBJECTIVE
  The purpose of this study was to compare different methods of measuring physical activity (PA) in women by the doubly labeled water method (DLW).
  
  
  METHODS
  Thirteen subjects participated in a 7-d protocol during which total daily energy expenditure (TDEE) was measured with DLW. Body composition, basal metabolic rate (BMR), and peak oxygen consumption were also measured. Physical activity-related energy expenditure (PAEE) was then calculated by subtracting measured BMR and the estimated thermic effect of food from TDEE. Simultaneously, over the 7 d, PA was assessed via a 7-d Physical Activity Recall questionnaire (PAR), and subjects wore secured at the waist, a Tritrac-R3D (Madison, WI), a Computer Science Application Inc. activity monitor (CSA; Shalimar, FL), and a Yamax Digi Walker-500 (Tokyo, Japan). Pearson-product moment correlations were calculated to determine the relationships among the different methods for estimating PAEE. Paired t-tests with appropriate adjustments were used to compare the different methods with DLW-PAEE.
  
  
  RESULTS
  There was no significant difference between PAEE determined from PAR and DLW. The differences between the two methods ranged from -633 to 280 kcal.d(-1). Compared with DLW, PAEE determined from CSA, Tritrac, and Yamax was significantly underestimated by 59% (-495 kcal.d(-1)), 35% (-320 kcal.d(-1)) and 59% (-497 kcal.d(-1)), respectively. VO2peak explained 43% of the variation in DLW-PAEE.
  
  
  CONCLUSIONS
  Although the group average for PAR-PAEE agreed with DLW-PAEE, there were differences in the methods among the subjects. PAEE determined by Tritrac, CSA, and Yamax significantly underestimate free-living PAEE in women.
authors.affiliation: Sport and Exercise Sciences Section, School of Physical Activity and Educational Services, Department of Statistics, The Ohio State University, Columbus, OH 43210, USA. leenders.1@osu.edu
authors.forename: N Y
authors.initials: NY
authors.lastname: Leenders
authors.forename: W M
authors.initials: WM
authors.lastname: Sherman
authors.forename: H N
authors.initials: HN
authors.lastname: Nagaraja
authors.forename: C L
authors.initials: CL
authors.lastname: Kien
mesh_terms: D000203:Activities of Daily Living; D000328:Adult; D001481:Basal Metabolism; D001823:Body Composition; D015992:Body Mass Index; D004734:Energy Metabolism / Q000502:physiology*; D016552:Ergometry / Q000295:instrumentation / Q000379:methods*; D005260:Female; D006801:Humans; D018670:Monitoring, Ambulatory / Q000295:instrumentation / Q000379:methods*; D010101:Oxygen Consumption; D012016:Reference Values; D012044:Regression Analysis; D013223:Statistics as Topic