title: Reliability of RT3 accelerometers among overweight and obese adults.
abstract: OBJECTIVE
  Accurate and reliable measurement of physical activity plays an important role in assessing effective lifestyle interventions for obesity. This study examined reliability of accelerometer-based estimates of physical activity levels of overweight and obese adults before and after a lifestyle weight loss program.
  
  
  METHODS
  Participants were overweight and obese (body mass index = 25-45 kg x m) members (n = 1592; 67% female, 42% African American) of the multicenter weight loss maintenance trial. They wore RT3 accelerometers during waking hours for 7 d at baseline and after a 6-month weight loss intervention that included diet and physical activity recommendations. Moderate-to-vigorous physical activity (MVPA) and MVPA occurring in bouts >or=10 min (bout MVPA) were assessed.
  
  
  RESULTS
  At baseline, wear time minimums of 10 and 6 h.d resulted in similar average minutes per day of MVPA (18.3 and 18.0 min) and MVPA bout minutes per day (6.9 and 6.7 min). Similar wear times occurred after the weight loss intervention for MVPA (27.0 and 26.8 min) and bout MVPA (15.1 and 15.0 min). Reliability measurements by intraclass correlation (ICC) were larger for 4 versus 2 d x wk minimum wear time for both MVPA and bout MVPA (4-d ICC = 0.27-0.44 and 2-d ICC = 0.19-0.38), but there was little increase in ICC comparing 4 (ICC = 0.27-0.44) and 7 d x wk (ICC = 0.30-0.46).
  
  
  CONCLUSIONS
  Longer wear time requirements did not result in significant increases in reliability. Using 4 d of data with >or=6 h x d of wear time optimized the balance between ICC and participant burden in overweight and obese adults before and after a weight loss intervention. Future investigations using accelerometers to estimate MVPA in overweight and obese samples can consider requiring less monitor wear time.
authors.affiliation: Department of Kinesiology, Towson University, 8000 York Road, Towson, MD 21252, USA. gjerome@towson.edu
authors.forename: Gerald J
authors.initials: GJ
authors.lastname: Jerome
authors.forename: Deborah Rohm
authors.initials: DR
authors.lastname: Young
authors.forename: Dan
authors.initials: D
authors.lastname: Laferriere
authors.forename: Chuhe
authors.initials: C
authors.lastname: Chen
authors.forename: William M
authors.initials: WM
authors.lastname: Vollmer
mesh_terms: D000054:Acceleration; D000328:Adult; D000368:Aged; D015992:Body Mass Index; D004734:Energy Metabolism; D015444:Exercise; D005080:Exercise Test; D005260:Female; D006801:Humans; D008297:Male; D008403:Mass Screening; D008875:Middle Aged; D018670:Monitoring, Ambulatory / Q000295:instrumentation*; D009043:Motor Activity; D053580:Muscle Strength; D009765:Obesity / Q000503:physiopathology*; D015203:Reproducibility of Results; D015431:Weight Loss