Most Americans go to sleep later on weekends than during the week, a new analysis confirms, reports Futurity.

The study of data from physical activity monitors suggests that younger people, especially, are more naturally prone to go to bed and wake up later. That adds evidence to support recent pushes for later middle and high school start times, the researchers say.

Most studies measure bedtime and the duration of sleep through self-reports from the sleepers themselves, says lead author Jacek Urbanek, assistant professor of medicine at the Johns Hopkins University School of Medicine.