CATEGORY: SLEEP & RECOVERY
People who went to bed earlier tended to be more physically active the next day, according to a large study that tracked sleep and movement through wrist-worn devices. Those who fell asleep around 9 p.m. logged roughly half an hour more moderate-to-vigorous activity the following day than those who turned in around 1 a.m. Because the study simply observed people’s own habits, it points to a link between sleep timing and next-day activity — not proof that going to bed earlier makes you move more.1
How the Study Worked
Researchers analyzed data from 19,963 adults who wore a fitness tracker (a WHOOP band) around the clock for a full year — nearly 6 million nights in all. The devices estimated when each person fell asleep, how long they slept, and how much moderate-to-vigorous activity (movement brisk enough to raise your heart rate, such as brisk walking or exercise) they did the next day. The team then checked the pattern against a separate group of 5,898 people who wore Fitbit devices, and it held up.
What the Numbers Showed
Bedtime stood out. Compared with people who typically fell asleep around 11 p.m. — close to the average — earlier sleepers did more the next day, up to about 20 extra minutes of moderate-to-vigorous activity for the earliest bedtimes. The gap between the earliest and latest sleepers was wider still: those asleep by 9 p.m. averaged about 28 more minutes of activity than those who went to sleep at 1 a.m.1
Timing, Not Just Hours of Sleep
The link also showed up within the same person from night to night. On nights when someone went to sleep earlier than their own usual time while still getting their typical amount of sleep, they tended to be the most active the following day. In other words, it wasn’t only how many hours people slept that tracked with activity — when they went to bed appeared to matter too.
What This Does and Doesn’t Mean
Because people chose their own sleep and activity, the study can’t prove one causes the other; early sleepers may differ in other ways, such as work schedules or morning routines. The data also came largely from people who chose to wear fitness trackers, who may be more active than average. What it adds is unusually detailed, real-world evidence that sleep timing and next-day movement are closely connected in everyday life.
Key Takeaways
- In wearable data from nearly 20,000 people, earlier bedtimes were linked to more next-day physical activity — about 28 extra minutes comparing a 9 p.m. bedtime with 1 a.m.
- The connection appeared night to night within individuals: going to sleep earlier than usual, while keeping the usual amount of sleep, was linked to the most activity the next day.
- This was an observational study, so it shows an association, not proof that earlier bedtimes cause more activity.
- If you’re weighing changes to your sleep schedule, your healthcare provider can help you find an approach that fits your health and daily life.
References
- Leota J, Czeisler MÉ, Le F, et al. Sleep duration and timing are associated with next-day physical activity: insights from two large-scale wearable sensor studies. Proceedings of the National Academy of Sciences. 2025;122(27):e2420846122. link