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Reliability of RT3 Accelerometers among Overweight and Obese Adults


Medicine & Science in Sports & Exercise: January 2009 - Volume 41 - Issue 1 - p 110-114
doi: 10.1249/MSS.0b013e3181846cd8
Basic Sciences

Purpose: 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·m−2) 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 ≥10 min (bout MVPA) were assessed.

Results: At baseline, wear time minimums of 10 and 6 h·d−1 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·wk−1 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·wk−1 (ICC = 0.30-0.46).

Conclusions: Longer wear time requirements did not result in significant increases in reliability. Using 4 d of data with ≥6 h·d−1 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.

1Department of Kinesiology, Towson University, Towson, MD; 2Johns Hopkins School of Medicine, Johns Hopkins University, Baltimore, MD; 3Department of Kinesiology, University of Maryland, College Park, MD; and 4Center for Health Research, Kaiser Permanente Northwest, Portland, OR

Address for correspondence: Gerald J. Jerome, Ph.D., Department of Kinesiology, Towson University, 8000 York Rd, Towson, MD 21252;

Submitted for publication March 2008.

Accepted for publication June 2008.

© 2009 American College of Sports Medicine