Abstract
Accelerometers are the most commonly used tool for objectively quantifying levels of moderate and vigorous physical activity (MVPA). However, physical activity results vary substantially depending on how the accelerometer data are processed. Specifically, little is known regarding how chosen monitor-wear criteria affect accelerometer outcomes. PURPOSE: The purpose of the study was to determine the influence of compliance criteria on accelerometer monitor compliance and resulting summary levels of MVPA. METHODS: The National Cancer Institute's SAS processing routines for NHANES 2005-2006 accelerometer data were modified to evaluate the influence of wear-time thresholds. The specific manipulations used included changes in the minimum number of wear-hours in a day (8h, 10h, and 12h) and the minimum number of valid days required (3d, 5d, and 7d) to be included in the data analyses. A total of 9 wear-time guidelines were established (3×3) ranging from least strict (8h/d on 3d) to most strict (12h/d on 7d). Descriptive statistics were used to evaluate the impact of these criteria on compliance and MVPA levels. RESULTS: A total of 7086 participants provided at least 1 d of accelerometer data. Depending upon the screening method, the proportion of compliant participants ranged from 12.5% (n = 884) to 85.9% (n = 6090), with MVPA estimates (Mean ± SD) ranging from 33.6 ± 52.7 min/d to 38.4 ± 66.0 min/d. When using the 10h/d wear-time threshold, 79.5% (MVPA = 35.4 ± 55.2 min/d), 59.8% (MVPA = 36.0 ± 60.2 min/d), and 24.7% (MVPA = 36.1 ± 74.2 min/d) of participants were compliant when requiring 3, 5, and 7 valid days, respectively. When using 5 valid days as the minimum threshold, 70.1% (MVPA = 34.2 ± 56.2 min/d), 59.8% (MVPA = 36.0 ± 60.2 min/d), and 42.3% (MVPA = 38.4 ± 66.0 min/d) of participants were compliant when requiring 8h/d, 10h/d, and 12h/d, respectively. CONCLUSIONS: Accelerometer compliance estimates vary substantially in the NHANES sample when different wear-time criteria are used to define compliance. Levels of MVPA also vary depending on the compliance method, with stricter compliance usually corresponding with higher physical activity estimates. The results demonstrate the importance of selecting appropriate monitoring criteria in processing accelerometer data.
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