Standardising the 'after-school' period for children's physical activity and sedentary behaviour

Issue addressed: Studies examining children's after-school physical activity (PA) and sedentary behaviours (SB) often use arbitrary times to signify the period start and end. A standardised time is required for future research examining this period. The aim of the present study was to compare children's after-school behaviour using three definitions of the after-school period, namely (1) end of school to 6 pm; (2) end of school to dinner time; and (3) end of school to sunset, to determine the extent of variability in PA and SB during the after-school period depending on the definition used. Methods: Children (n = 308; aged 8 years) from the Melbourne Transform-Us! intervention wore an accelerometer and a subsample (n = 112) wore an activPAL inclinometer in 2010. The end of school bell time was obtained from the child's school, parents completed a 2-day log reporting their child's dinner time and sunset times were obtained from Geoscience Australia. ActiGraph accelerometers assessed the proportion of time spent sedentary (SED) and that spent in light (LPA), moderate (MPA) and moderateto-to-vigorous (MVPA) PA during the three time periods; activPAL inclinometers assessed the proportion of time spent sitting (SIT). Results: Apart from the end of school time (3:30 pm), dinner (range 3:30 pm-8:40 pm) and sunset (range 5: 07 pm-7:34 pm) times varied. Despite this, there were no significant differences in estimates of the proportions of time children spent in SED, LPA, MPA, MVPA or SIT between the three after-school periods examined. Conclusion: Given the small differences in SED, PA and SIT during the after-school period regardless of the definition (6 pm, sunset or dinner time), it appears that applying a standardised definition of end of school to 6 pm is acceptable for defining children's PA and SB during the after-school period.