Improving physical activity assessment in prepubertal children with high-frequency accelerometry monitoring: A methodological issue

Abstract

Objective

The aim of this study was to examine the duration of physical activity (PA) bouts in prepubertal children with high-frequency accelerometry monitoring.

Methods

Thirteen boys and thirteen girls (aged 8–10 years) from one school in North of France had their PA recorded during 7 days using a uniaxial Actigraph accelerometer. To examine PA behavior patterns, the epoch was set at 2 s. Times spent in light (LPA), moderate (MPA), vigorous (VPA) and very high (VHPA) intensity activity and the daily number of PA bouts of different durations (from 2 to 1200 s) were calculated for each intensity level. Data were collected in 2004.

Results

The mean duration of PA bouts was 70.8 ± 13.2 s for LPA, 9.0 ± 2.8 s for MPA, 4.7 ± 1.2 s for VPA and 3.9 ± 1.6 s for VHPA. For the whole population, 80% of MPA, 93% of VPA and 96% of VHPA lasted less than 10 s. Although times spent in VPA and VHPA represented 2.4% of the total PA time, VPA and VHPA bouts accounted for 36.1 ± 5.8% of the total amount of PA.

Conclusion

Children's PA pattern is highly transitory and intermittent whatever its intensity. Physical activity assessed with a sampling interval related to children's behavior may improve our understanding of their PA patterns.

Introduction

There is increasing evidence that physical activity (PA) during childhood and adolescence has an important impact on short- and long-term health and behavior outcomes (Strong et al., 2005). In a review on interrelationships between PA and health, Biddle et al. (2004) emphasized the need to develop a greater understanding of PA in youth. To establish the links between PA, health and disease, they stated that an accurate assessment of PA is necessary to objectively highlight the “real” patterns of children's PA over time. From a video observation, Bailey et al. (1995) reported that the nature of children's HPA pattern is intermittent and characterized by rapid changes from rest to PA of vigorous intensities, which makes these activities even more difficult to recall and quantify, especially in terms of intensity and duration. However, if video observation is a standard in PA assessment, this methodology is time consuming, needs trained staff and every event must be observable and quantifiable. Assessment of human body movement with activity monitors based on accelerometry is also a direct objective way of measuring PA (Sirard and Pate, 2001). These devices convert recorded accelerations to a quantifiable signal referred to as “counts” and sum these counts over a selected time interval called “epoch”. However, in most of the studies involving children, the epoch has been set at 1 min (Trost et al., 2002, Riddoch et al., 2004). Using such epoch can hardly reflect children's PA patterns in free-living conditions. Nilsson et al. (2002) demonstrated that there was a significant discrepancy between the recorded times spent at different levels of PA (from low to high-intensity) according to the epoch settings, particularly for high and very high intensities. Henceforth, to describe more accurately children's daily PA patterns, it appears necessary to monitor the children with a more consistent sampling interval related to their PA, which can be done using accelerometry. This study aimed to analyze the patterns of children's physical activity intensity and duration (temporal patterning) over time, using a high-frequency activity monitoring.