Related Experiment Video
Updated: Dec 25, 2025
Visualization of Intensity Levels to Reduce the Gap Between Self-Reported and Directly Measured Physical Activity
Published on: March 7, 2019
Reproducibility of objectively measured physical activity: Reconsideration needed
Eivind Aadland1, Ada Kristine Ofrim Nilsen1, Einar Ylvisåker1
1Faculty of Education, Arts and Sports, Department of Sport, Food and Natural Sciences, Western Norway University of Applied Sciences , Sogndal, Norway.
Insights
The length of accelerometer monitoring for physical activity (PA) reliability depends on data analysis. Shorter monitoring periods may suffice, but analysis methods significantly impact results and required duration.
Area of Science:
- Pediatrics
- Sports Science
- Biomedical Engineering
Background:
- Objective measurement of physical activity (PA) using accelerometers is crucial in pediatric research.
- The reliability of accelerometer data is essential for accurate PA assessment.
- Previous studies suggest varying monitoring durations are needed, but the influence of data resolution is unclear.
Purpose of the Study:
- To compare the reliability of accelerometer-determined PA using different data resolutions.
- To determine the optimal monitoring period length for reliable PA assessment in children.
- To evaluate how different analytical approaches affect the estimation of PA reliability.
Main Methods:
- 221 Norwegian children (2-6 years) wore accelerometers (ActiGraph GT3X+) for 2-3 periods of 14 days.
- Reliability was assessed using intra-class correlation (ICC) for 1-14 days of monitoring.
- Data resolution (hour-by-hour, day-by-day, week-by-week, period-by-period) and Spearman-Brown formula were used for estimation.
Main Results:
- Measured reliability plateaued after 5-6 days of monitoring.
- Estimated monitoring duration to achieve ICC=0.80 varied significantly by data resolution (3.9-87.7 days).
- Reliability could not be accurately estimated from a single data resolution.
Conclusions:
- The analytical approach and data resolution critically influence the perceived reliability of accelerometer-measured PA.
- Current methods for determining monitoring duration may overestimate or underestimate the required period.
- Reconsideration of PA data analysis and interpretation is necessary for accurate reproducibility.
Abstract:
Reliability of accelerometer-determined physical activity (PA), and thus the required length of a monitoring period, appears to depend on the analytic approach used for its calculation. We compared reliability of objectively measured PA using different resolution of data in a sample of 221 Norwegian 2-6-year-old children providing 2-3 valid 14-day periods of accelerometer monitoring (ActiGraph GT3X+) during September-October, January-February, and May-June 2015-2016. Reliability (intra-class correlation [ICC]) was measured for 1-14 days of monitoring across the measurement periods using linear mixed effect modelling. These results were compared to reliability estimated using different resolution of data using the Spearman-Brown formula. The measured reliability improved only marginally with increased monitoring length and levelled off after 5-6 days. Estimated reliability differed substantially when derived from different resolution of data: 3.9-5.4, 6.7-9.2, 13.4-26.7 and 26.3-87.7 days of monitoring was required to achieve an ICC = 0.80 using an hour-by-hour, a day-by-day, a week-by-week and a period-by-period approach, respectively. Reliability could not be correctly estimated from any single resolution of data. We conclude that reconsideration is needed with regard to how reproducibility of objectively measured PA is analysed and interpreted.
