Associations of objectively assessed sleep and physical activity in 11-year old children

Aim: Objective methods were used to evaluate children's sleep and physical activity over several days in order to test the hypotheses that: (1) low average sleep duration and/or sleep efficiency are linked to a low amount of physical activity; and (2) a reduction in sleep quantity and/or sleep efficiency during the night is followed by a decrease in physical activity the following day. Methods: This is a multi-centre, observational study involving 276 children, aged 10.5-12 years, from diverse urban settings in Croatia, Slovenia and the US. Sleep and activity were monitored for 2-6 days (median = 4) using the Sensewear Armband (TM) multi-sensor body monitor. Results: While average sleep duration and efficiency were unrelated to physical activity, within-subjects associations revealed that an extra hour spent in bed during the night was followed by a 16-minute decrease in moderate-to-vigorous physical activity (p<0.001). This was accompanied by a 4.5 kJ/kg and 5.9 kJ/kg lower total daily energy expenditure in boys and girls, respectively (p<0.001). Conclusions: This study found no evidence for a link between short sleep and low or reduced physical activity.