Sweat Doesn’t Guarantee Good Night’s Sleep, Study Says

A good workout doesn’t guarantee a sounder night’s sleep.

The idea that people need sleep to recover from the wear and tear of exercise is overrated, a researcher says.

“The evidence shows exercise just does not have that much effect on sleep,” said researcher Shawn Youngsted of UC San Diego.

Youngsted’s review, a meta-analysis, culled 38 studies and pooled data from 401 research subjects to cover just about all phases of sleep from nodding off to waking up. The paper was an attempt to determine whether popular preconceptions about the benefits of sleep matched the facts. It was published in the American Sleep Disorders Assn. and Sleep Research Society journal, Sleep.

“Most people think that, if they had a physically active day, they would sleep better,” Youngsted said. But the research indicates that an active day doesn’t make much difference, he said.

For instance, the time spent going from wakefulness to sleep does not differ in any meaningful way between exercisers and non-exercisers, Youngsted said. Nor does stage 1 sleep, the twilight state of nodding off, he said.

Exercisers did have a bit under two minutes more stage 2 sleep, the study found. But stage 2 accounts for about half of all time sleeping, so there was no real advantage, Youngsted said.

There was a similar benefit of, on average, less than two minutes, in slow wave sleep, which is the deepest sleep, and which accounts for about 20% of all sleep, Youngsted said. But there’s not much evidence that the extra slow wave slumber will help anyone work better or play harder the next day, he said.

Exercisers had about six minutes less REM sleep, the dreaming stage that comprises another 20% of sleep time, the review found. “I’m not sure what to make of that finding,” Youngsted said. For one thing, dreaming can take place in other sleep stages, he said.

In all, exercisers had about 10 minutes more sleep than non-exercisers, the study found. And people who exercised more also slept longer, it found.

Because the average sleep period was about seven hours, the difference doesn’t mean exercisers need--or benefit from--appreciably more sleep, Youngsted said. But it doesn’t rule out a greater need for sleep after very long, hard exercise, he said.

And the studies examined only normal sleepers, so it’s not known if poor sleepers would improve their sleep a lot after exercise, Youngsted said.

The studies also looked at what happened after a single exercise session, not for any cumulative effects built up in a habit of exercise.

“The most interesting group was not able to be done,” said researcher Ofreu Buxton of the University of Chicago. “The chronic exercise group could show the greatest benefits.”