title: Population-referenced percentiles for waist-worn accelerometer-derived total activity counts in U.S. youth: 2003 - 2006 NHANES.
abstract: 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 age- and gender-specific percentiles for daily TAC, minutes of MVPA, and minutes of LPA in U.S. youth ages 6 - 19 y.
  
  
  METHODS
  Data from the 2003 - 2006 NHANES waist-worn accelerometer component were used in this analysis. The sample was composed of youth aged 6 - 19 years with at least 4 d of ≥ 10 hours of accelerometer wear time (N = 3698). MVPA was defined using age specific cutpoints as the total number of minutes at ≥4 metabolic equivalents (METs) for youth 6 - 17 y or minutes with ≥2020 counts for youth 18 - 19 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.
  
  
  CONCLUSIONS
  Population referenced TAC/d percentiles for U.S. youth ages 6-19 y provide a novel means of characterizing the total activity volume performed by children and adolescents.
authors.affiliation: Dept. of Kinesiology, Recreation & Sports Studies, The University of Tennessee, Knoxville, Tennessee, United States of America.
authors.forename: Dana L
authors.initials: DL
authors.lastname: Wolff-Hughes
authors.affiliation: Dept. of Kinesiology, Recreation & Sports Studies, The University of Tennessee, Knoxville, Tennessee, United States of America.
authors.forename: David R
authors.initials: DR
authors.lastname: Bassett
authors.affiliation: Dept. of Kinesiology, Recreation & Sports Studies, The University of Tennessee, Knoxville, Tennessee, United States of America.
authors.forename: Eugene C
authors.initials: EC
authors.lastname: Fitzhugh
mesh_terms: D061725:Accelerometry / Q000295:instrumentation / Q000592:standards*; D000293:Adolescent; D002648:Child; D004734:Energy Metabolism; D015444:Exercise / Q000502:physiology*; D005260:Female; D006801:Humans; D008297:Male; D009043:Motor Activity / Q000502:physiology*; D009749:Nutrition Surveys; D013997:Time Factors; D014481:United States