Abstract
BackgroundKnowledge of the reproducibility of domain-specific accelerometer-determined physical activity (PA) estimates are a prerequisite to conduct high-quality epidemiological studies. The aim of this study was to determine the reproducibility of objectively measured PA level in children during school hours, afternoon hours, weekdays, weekend days, and total leisure time over two different seasons.MethodsSix hundred seventy six children from the Active Smarter Kids study conducted in Sogn og Fjordane, Norway, were monitored for 7 days by accelerometry (ActiGraph GT3X+) during January–February and April–May 2015. Reproducibility was estimated week-by-week using intra-class correlation (ICC) and Bland-Altman plots with 95% limits of agreement (LoA).ResultsWhen controlling for season, reliability (ICC) was 0.51–0.66 for a 7-day week, 0.55–0.64 for weekdays, 0.11–0.43 for weekend days, 0.57–0.63 for school hours, 0.42–0.53 for afternoon hours, and 0.42–0.61 for total leisure time. LoA across models approximated a factor of 1.3–2.5 standard deviations of the sample PA levels. 3–6 weeks of monitoring were required to achieve a reliability of 0.80 across all domains but weekend days, which required 5–32 weeks.ConclusionReproducibility of PA during leisure time and weekend days were lower than for school hours and weekdays, and estimates were lower when analyzed using a week-by-week approach over different seasons compared to previous studies relying on a single short monitoring period. To avoid type 2-errors, researchers should consider increasing the monitoring period beyond a single 7-day period in future studies.Trial RegistrationClinicalTrials.gov, NCT021324947. Registered on 7 April 2014.
Highlights
Knowledge of the reproducibility of domain-specific accelerometer-determined physical activity (PA) estimates are a prerequisite to conduct high-quality epidemiological studies
The children included in the present analyses were more Sedentary time (SED) (mean 3.7 (1.5–5.9) min/day, p = .001), and demonstrated lower overall (− 41 (− 64–-18) cpm, p = .001) and intensity-specific PA levels (MPA: − 1.7 (− 2.4–-0.9) min/day; vigorous PA (VPA): − 1.3 (− 2.1–-0.6) min/day; moderate-to-vigorous PA (MVPA): − 3.0
Reliability for a 7-day period was lower than in most previous studies relying on a single monitoring period, and reliability for leisure time and weekend days was lower than for school hours and week days
Summary
Knowledge of the reproducibility of domain-specific accelerometer-determined physical activity (PA) estimates are a prerequisite to conduct high-quality epidemiological studies. There are many unresolved issues regarding data reduction and quality assessment of accelerometry data to determine physical activity (PA) and sedentary behavior (SED) These challenges leads to great variation in procedures used and criteria applied to define a valid measurement [1]. As behavior vary greatly over time, an important aspect of accelerometer measurements is how many days or periods of measurement that need to be included to obtain reliable estimates of habitual activity level. This is true when children live in an area with a significant change in weather during different seasons [2,3,4]. Many studies target in-school versus out-of-school, or weekday
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