Adequate sleep and physical exercise are cornerstones of a healthy lifestyle, yet, unfortunately, adolescents in the United States are failing to meet the recommendations for both of these behaviors. In 2023, for example, only about a quarter of high school students met the guideline for daily exercise, and another recent survey found that over 75% of U.S. adolescents do not get the recommended minimum of eight hours of sleep per night.

To explore the relationship between sleep and activity levels among U.S. adolescents, researchers at the University of Minnesota School of Public Health (SPH) conducted a study to analyze how their sleep is contributing to sedentary behavior and overall activity levels. The study, published in the Journal of Physical Activity and Health, suggests that when teens sleep longer, and at times better aligned with their biological clocks, they are less likely to spend their waking hours in sedentary activities, and are more likely to engage in physical activity.

To conduct the study, SPH researchers analyzed data from 260 ninth-grade students in Minnesota. All student participants wore wrist-mounted devices continuously for seven days, allowing researchers to objectively measure sleep duration, sleep timing, sleep efficiency, and physical activity levels—including sedentary time, light physical activity, and moderate to vigorous physical activity. Data analyzed by researchers also included demographic factors such as sex, race, and parental education levels.

The paper found:

• Longer sleep was associated with less sedentary time. For each additional hour of sleep, adolescents spent about 26 fewer minutes sedentary on weekdays and 19 fewer minutes sedentary on weekends, suggesting that extra sleep time may replace inactive waking behaviors.
• Closer alignment with adolescents’ natural circadian rhythms (i.e., internal clock) was linked to higher activity levels. Shifting to a later sleep schedule–measured by the halfway point between falling asleep and waking up–was linked to higher physical activity levels. Every hour later in this ‘sleep midpoint’ on weekdays was associated with 14.2 more minutes of light physical activity and 3.1 additional minutes of moderate to vigorous physical activity.
• More time spent sleeping was not associated with reduced activity levels. Sleep duration was not related to time spent doing moderate to vigorous physical activity on either weekdays or weekends, suggesting that increased sleep did not come at the expense of exercise.

“Both sleep and physical activity shape long-term risks for obesity, heart disease, Type 2 diabetes, and other chronic diseases, so we wanted to examine the relationship between these behaviors  in young people,” said Kayla Johnson, SPH researcher and lead author. “Our findings suggest that adolescents who get more sleep or whose sleep schedules are better aligned with their biological rhythms, rather than earlier or more forced bedtimes, tend to spend less time sedentary without losing meaningful physical activity—findings that could have implications for policies like delayed school start times.”

It is important to understand how sleep and physical activity behaviors develop over time, how these behaviors might vary across populations and what factors could influence these patterns. Daily behaviors in adolescence can set the stage for lifelong patterns.