Impact of methodological decisions on accelerometer outcome variables in young children

Abstract

Background: The impact of accelerometer-related methodological decisions relating to the assessment of physical activity and sedentary time has not been conclusively determined in young children.Objectives: To determine the effects of epoch and cutoff points on the assessment of physical activity and sedentary time and to determine the accelerometer wear time required to achieve reliable accelerometer data in children.Design: Children were recruited from centers at Ghent, Glasgow, Gothenburg, and Zaragoza.Methods: Physical activity was assessed for 1 week in 86 children (41 girls, 45 boys; mean age 7±2 years) by uniaxial accelerometry. The epoch was set at 15s and reintegrated to 30 and 60s. Time spent sedentary and in moderate and vigorous physical activity (MVPA) was assessed using a range of cutoff points. Number of days required to achieve 80% reliability was predicted using the Spearman-Brown Prophecy formula. Results: The Reilly cutoff points (o1100 counts per min (CPM)) indicated less sedentary time per day when comparing 15 vs30s and 15 vs 60s epochs: 570±91 vs 579±93min and 570±91 vs 579±94min, respectively; Po0.05. Pate cutoff points(4420counts per 15s) reported more MVPA time per day compared with Sirard (890counts per 15s) and Puyau cutoff points(43200counts per min) using 15s epoch: 78 (4–197)min (median (range) vs 18 (1–80) min and 24 (1–100)min, respectively; Po0.001. Compliance with guidelines of at least 60min MVPA was 84, 78 and 73% for Pate cutoff points using 15, 30, and 60sepochs, respectively, but 0% for Sirard and Puyau cutoff points across epochs. The number of days required to achieve 80%reliability for CPM, sedentary, and MVPA time was 7.4–8.5 days. Conclusion: Choice of epoch and cutoff point significantly influenced the classification of sedentary and MVPA time and observed compliance to the MVPA guidelines.