The relationship between sleep and physical activity in children

The aim of this thesis was to investigate the relationship between physical activity and sleep in children. The thesis has contributed to the empirical body of evidence with three studies. Study 1 (Chapter 2) was a systematic review and meta-analysis of the literature investigating the relationship between physical activity and sleep in children. Overall, the meta-analysis found little association between physical activity and sleep (r = .02, 95% confidence interval = -.03 to .07) and no examined variables significantly moderated the overall effect. Exploratory analyses showed only two significant but weak associations for vigorous physical activity with sleep (r = .09, 95% CI = .01 to .17, I2 = 66.3%), specifically sleep duration (r = .07, 95% CI = .00 to .14, I2 = 41.1%). Study 2 (Chapter 3) investigated both longer-term (i.e., habitual) and day-to-day associations among a large sample of Australian children. Longer-term, the trajectories of change in physical activity over time showed little association with the trajectory of change in sleep. The day-to-day analysis showed that increased physical activity improves sleep the following night and that better sleep predicts an increase in physical activity the following day. Study 3 (Chapter 4) investigated accelerometer wear-time criteria for how valid a night should be and the total number of valid nights that are needed to get reliable estimates of habitual sleep duration, sleep efficiency, time in bed, and sleep timing. The study found that, generally, 5 nights of valid data is enough to get acceptable estimates of habitual sleep behaviour. Implications, strengths, and limitations of the thesis are discussed in Chapter 5.