Accelerometer-Derived Physical Activity in Preschoolers: A G-Force Histogram Analysis

Introduction Accelerometers have been seen as gold-standard objective tool for monitoring childrens’ habitual physical activity. To become biologically meaningful, the activity levels have generally been estimated on the basis of cut-off points. However, there is a lack of general agreement on how to choose the cut-off points (Bornstein et al., 2011). The aim of this study was to describe habitual physical activity of preschool-aged children both by means of an acceleration histogram and the cut-off points (van Cauwenberghe et al., 2010).

Methods The subjects were 4-to-6-year-old children attending all-day day-care in kindergarten (n = 17; 10 boys; mean age 5.5 ± 0.6 years). Physical activity was measured over 6 days (at least 1 weekend day) using triaxial Gulf Coast Data Concepts X6-1a accelerometers with a dynamic range of ±6g. The devices were carried in an elastic belt that was firmly worn on the subjects’ waist (Finni et al. 2011). The direction of the acceleration was ignored. Magnitudes were band-pass filtered (0.25 Hz … 11 Hz), and values below 0.05g were filtered out. Physical activity counts were calculated by summing over 15-second epochs and multiplying by a device-specific factor that was derived from simultaneous recordings with the X6-1a and ActiGraph GT3X.

Results Physical activity was monitored for an average of 4.7 days (12.2 ± 2.5 hours/d). The average time children spent at acceleration level under 0.05g, between 0.05-2g and over 2g each day were 658.0 ± 133.3 (89.6%), 48.1 ± 12.1 min (6.6%) and 28.1 ± 12.2 min (3.8%), respectively. Mean total activity was 664 ± 295 counts per minute. Children participated on average 36.7 ± 14.6 minutes per day in light physical activity and 52.7 ± 35.4 minutes per day in moderate-to-vigorous physical activity.

Discussion To our knowledge this is the first time to describe preschoolaged childrens’ physical activity by g-force histogram using accelerometers. The g-force histogram conserves valuable raw data gathered and is thus promising tool for assessing both the amount and quality of preschool-aged childrens’ physical activity. In further research, g-force histogram could be useful for assessing, for instance, physical activities’ dose-response rate relating to childrens’ bone and motor skill development. Further study is also needed to map behavioural meanings into g-force histogram values.

References Bornstein DB, Beets MW, Byun W, McIver K. (2010). J Sci Med Sport, 14, 504-511. Finni T, Sääkslahti A, Laukkanen A, Pesola A, Sipila S. (2011). BMC Public Health, 11: 944. van Cauwenberghe E, Labarque V, Trost SG, De Bourdeaudhuij I, Cardon G. (2010). Int J of Pediatr Obes, 6 (2-2), 582-589.