How many hours are enough? Accelerometer wear time may provide bias in daily activity estimates

Stephen D. Herrmann, Tiago V. Barreira, Minsoo Kang, Barbara E. Ainsworth

Research output: Contribution to journalArticlepeer-review

91 Scopus citations


Background: There is little consensus on how many hours of accelerometer wear time is needed to reflect a usual day. This study identifies the bias in daily physical activity (PA) estimates caused by accelerometer wear time. Methods: 124 adults (age = 41 ± 11 years; BMI = 27 ± 7 kg·m-2) contributed approximately 1,200 days accelerometer wear time. Five 40 day samples were randomly selected with 10, 11, 12, 13, and 14 h·d-1 of wear time. Four semisimulation data sets (10, 11, 12, 13 h·d-1) were created from the reference 14 h·d-1 data set to assess Absolute Percent Error (APE). Repeated-measures ANOVAs compared min·d-1 between 10, 11, 12, 13 h·d-1 and the reference 14 h·d-1 for inactivity (<100 cts·min-1), light (100-1951 cts·min-1), moderate (1952-5724 cts·min-1), and vigorous (≥5725 cts·min-1) PA. Results: APE ranged from 5.6%-41.6% (10 h·d-1 = 28.2%-41.6%; 11 h·d -1 = 20.3%-36.0%; 12 h·d-1 = 13.5%-14.3%; 13 h·d-1 = 5.6%-7.8%). Min·d-1 differences were observed for inactivity, light, and moderate PA between 10, 11, 12, and 13 h·d-1 and the reference (P < .05). Conclusions: This suggests a minimum accelerometer wear time of 13 h·d-1 is needed to provide a valid measure of daily PA when 14 h·d-1 is used as a reference.

Original languageEnglish (US)
Pages (from-to)742-749
Number of pages8
JournalJournal of Physical Activity and Health
Issue number5
StatePublished - Jul 2013
Externally publishedYes


  • Accelerometry
  • Measurement
  • Physical activity
  • Physical activity assessment

ASJC Scopus subject areas

  • Public Health, Environmental and Occupational Health
  • Physical Therapy, Sports Therapy and Rehabilitation
  • Epidemiology
  • Orthopedics and Sports Medicine


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