Physical Activity, Inactivity, and Health

Background: The total activity volume performed is an overall measure that takes into account the frequency, intensity, and duration of activities performed. The importance of considering total activity volume is shown by recent studies indicating that light physical activity (LPA) and intermittent moderate-to-vigorous physical activity (MVPA) have health benefits. Accelerometer-derived total activity counts (TAC) per day from a waist-worn accelerometer can serve as a proxy for an individual's total activity volume. The purpose of this study was to develop ageand genderspecific percentiles for daily TAC, minutes of MVPA, and minutes of LPA in U.S. youth ages 619 y. Methods: Data from the 20032006 NHANES waistworn accelerometer component were used in this analysis. The sample was composed of youth aged 619 years with at least 4 d of >= 10 hr of accelerometer wear time (N = 3698). MVPA was defined using age specific cutpoints as the total number of minutes at metabolic equivalents (METs) for youth 617 y or minutes with 2020 counts for youth 1819 y. LPA was defined as the total number of minutes between 100 counts and the MVPA threshold. TAC/d, MVPA, and LPA were averaged across all valid days. Results: For males in the 50th percentile, the median activity level was 441,431 TAC/d, with 53 min/d of MVPA and 368 min/d of LPA. The median level of activity for females was 234,322 TAC/d, with 32 min/d of MVPA and 355 min/d of LPA. Conclusion: Population referenced TAC/d percentiles for U.S. youth ages 619 y provide a novel means of characterizing the total activity volume performed by children and adolescents.