Longitudinal changes in objectively measured physical activity differ for weekdays and weekends among Chinese children in Hong Kong Energy balance-related behaviours

Background: Cross-sectional investigation showed that Chinese children in Hong Kong were more physically active on weekends than weekdays, which is contrary to previous findings. However, little is known as to whether these time-segment-specific differences persist with age. This study aimed to compare the 2-year changes in accelerometer-assessed physical activity (PA) and sedentary time (ST) between weekdays and weekends among Chinese children in Hong Kong. Methods: Children aged 6-8 years were recruited from primary schools in Hong Kong. Time spent in ST (<100 counts per minute [cpm]), moderate-to-vigorous PA (MVPA), and light-intensity PA (LPA) were measured by accelerometer at baseline and then at 1-year and 2-year follow-ups. Mean annual changes were determined using mixed-effects linear models for children who provided 3-day valid data (including 1 weekend day) for at least two time points (n = 412). Magnitude of changes between weekdays and weekends was compared using age × time-segment interactions. Results: At each assessment wave, the percentage of time spent in MVPA (% MVPA) and LPA (% LPA) was consistently high, whereas the percentage of time spent in ST (% ST) was lower on weekends than weekdays. A decrease in % MVPA was found for both weekdays (mean annual change: boys, -0.7, 95 % CI = -0.9 to -0.1; girls, -0.8, 95 % CI = -1.0 to -0.6) and weekends (boys, -1.2, 95 % CI = -1.5 to -0.9; girls, -1.4, 95 % CI = -1.6 to -1.1). An increase was found in % ST for both weekdays (boys, 1.3, 95 % CI = 0.7 to 1.9; girls, 2.4, 95 % CI = 1.9 to 3.3) and weekends (boys, 1.8, 95 % CI = 1.1 to 2.5; girls, 2.6, 95 % CI = 1.9 to 3.3). Mean annual change in MVPA time (min) was greater on weekends than weekdays (difference: boys, 3.0, 95 % CI = 0.3 to 5.7; girls, 3.5, 95 % CI = 1.1 to 5.8). Conclusions: Age-related decline in MVPA was more marked on weekends than weekdays. Interventions to hinder age-related changes in PA and ST should target both time segments, but weekends warrant particular attention for interventions targeting PA maintenance due to the greater declines.