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Depending on the time of day they happen, intense workouts can have a negative or positive impact on your sleep.
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  • New research shows that high-intensity exercise less than 2 hours before bedtime can have a negative impact on sleep.
  • Exercising earlier in the evening leads to better sleep quality.
  • But high-intensity exercise also triggers physiological changes that can delay sleepiness.

Moderate-intensity exercise is often recommended as a way to help you sleep better, with high-intensity exercise being discouraged.

However, there is much we do not know about the interplay between exercise and sleep quality.

To learn more about the link, researchers at Concordia University conducted an analysis of the data from previous studies dealing with the effect of high-intensity exercise on sleep.

The researchers found, overall, that exercise that was completed 2 or more hours before bedtime aided sleep quality. Participants fell asleep faster and slept longer.

Exercise that occurred closer to bedtime, however, had a negative impact, causing people to take longer to fall asleep and to sleep for a shorter amount of time.

In order to conduct the study, the team did a review of the literature dealing with this topic in six major scientific databases.

They were able to identify a total of 15 trials involving 194 people.

Participants were either sedentary or physically fit good sleepers between the ages of 18 and 50.

Each study used either objective measures, like polysomnography or actigraphy, or the participants’ subjective judgment to assess how high-intensity exercise had affected people’s sleep.

The team then conducted an analysis of the data they had gathered.

One of the outstanding findings of their analysis was how the timing of exercise affected sleep.

When exercise ended at least 2 hours before bedtime, people fell asleep more quickly and slept for longer. This was especially true for the more sedentary individuals.

However, if exercise ended less than 2 hours before bedtime, the opposite occurred. People took longer to fall asleep and did not sleep as long.

The researchers further found that exercise performed between 30 and 60 minutes of time also improved sleep onset and duration.

Cycling exercises were the most beneficial in helping people fall asleep and sleep deeply, according to the team.

However, the study also mentioned that high-intensity exercise, no matter when it occurred, slightly decreased the rapid-eye-movement (REM) state of sleep. REM sleep is associated with dreaming. Some studies suggest that decreased REM sleep may have a negative effect on cognitive tasks, according to the study authors.

On the other hand, according to Tamara Hew-Butler, DPM, PhD, FACSM, an associate professor in exercise and sport science at Wayne State University’s College of Education, high-intensity exercise causes a strong sympathetic nervous system response called the “fight or flight” response.

The fight or flight response is a survival response that our bodies have in the face of threats, real or perceived. It prepares us to either fight against those threats or to run away to safety by increasing heart rate, blood pressure, and breathing rate.

This same physiological response is triggered by intense exercise, leaving you prepared for action, not sleep.

Hew-Butler said it is commonly thought that high-intensity exercise performed within about 3 hours of bedtime can interfere with sleep — especially falling asleep — because it increases arousal, core body temperature, stress, and sympathetic hyperactivity.

It can also cause a “phase delay” in circadian rhythm, she explained, causing you to stay up later and wake up later due to delayed release of melatonin, the hormone that triggers nighttime sleepiness.

Yasi Ansari, MS, RDN, a registered dietitian nutritionist specializing in sports nutrition and National Media Spokesperson for the Academy of Nutrition and Dietetics, said that this review suggests an evening of high-intensity exercise may be beneficial for nighttime sleep quality, if it’s completed earlier in the evening.

However, if you exercise closer to the time you settle down for the night, it could disrupt your sleep.

Regardless of what the study indicates, Ansari suggests that you should tailor your exercise habits to your own individual body.

“I encourage readers to understand what works best for them and the type and training time that supports their sleep,” she said.

“While there is research out there for us, and research-supported recommendations, it is also important for each person to see what works best for them, their energy, and sleep quality.”