Máchal J, et al. - In order to assess the effects of physical activity and fitness on sleep timing parameters in adolescence, the development of sleep timing between age 8 and 15 was investigated and its association with physical fitness at age 15 in 787 adolescents (408 males, 379 females) was determined. In contrast to the existing hypotheses suggesting an association of low physical activity and fitness with shorter sleep duration and high BMI in a generally non-obese adolescent population without severe sleep restriction, this study recognized no association of sports activity at age 11 with sleep timing at age 15. However, they noted a link between higher BMI and delayed bedtime and higher physical fitness.