You've heard me say it before: Exercise is good for sleep. Research has documented the benefits of exercise to improving sleep patterns. Exercise lifts mood and reduces stress. It can strengthen circadian rhythms, promoting daytime alertness and helping bring on sleepiness at night. Exercise has been shown to improve sleep for people with sleep disorders, including insomnia and obstructive sleep apnea. A recent National Sleep Foundation poll found that regular exercisers were significantly more likely to report sleeping well on most nights than people who were not physically active. Research has shown exercise can help to improve not only the quantity of sleep but also the quality: Studies show daytime physical activity may stimulate longer periods of slow-wave sleep, the deepest and most restorative stages of sleep.
A new study takes a closer look at the relationship between exercise and sleep. The results confirm some of what we already know: A regular exercise routine does contribute to improved sleep. But this research also sheds some light on the complexity of the relationship between sleep and exercise. In particular, the study suggests that exercise may not have an immediate impact on sleep, but in fact may take several weeks or months to significantly change sleep. Sleep, on the other hand, may have a very short-term effect on exercise. According to these results, a poor night's sleep can have a negative effect on next-day workouts.
Researchers at Northwestern University's Feinberg School of Medicine investigated the bi-directional relationship between sleep and exercise, studying not just the effects of exercise on sleep, but also the effects of sleep on exercise. They used data from an earlier sleep study that examined the impact of moderate, regular physical activity on sleep, mood and quality of life among a group of adults 55 years and older, all of whom had chronic insomnia. None of the subjects exercised regularly. Researchers divided the subjects into two groups. One group remained with their sedentary routine, while the other group began a regular exercise program that included three to four 30-minute sessions per week of moderate aerobic exercise. After 16 weeks, the exercise group had improved sleep significantly and across several measures of sleep, including sleep duration and sleep quality, as well as daytime sleepiness. The exercisers also reported improvements to their moods and to their quality of life.
For the current study, researchers looked closely at this data, this time to see how quickly exercisers saw improvements to their sleep. They wanted to know whether individual daytime exercise sessions led to better sleep later that same night. They also investigated what impact sleep had on exercise the following day. Their analysis revealed that though exercise did have a significant positive impact on sleep, its effects were not immediate:
- Individual exercise sessions did not have an immediate effect on sleep. Researchers found no improvements to sleep from exercise on a day-to-day basis.
- As far as two months into the 16-week study period, the exercising group had experienced no significant improvements to their sleep. By the end of the 16 weeks, however, the exercising group had seen their sleep quality and sleep quantity rise significantly.
- Though exercise did not appear to have an immediate impact on sleep, analysis showed that sleep did have an immediate -- and significant -- effect on exercise. Subjects had shorter exercise sessions after nights when they slept poorly. This relationship of poor sleep to diminished exercise was strongest among subjects whose sleep was the most challenged at the beginning of the study period.
This news might seem disappointing, especially for those people who hoped that exercise might provide a quick fix for sleep problems. But there are a few important points to keep in mind. First, this study did confirm that exercise can have a dramatic effect on sleep. Exercising subjects in the 16-week study eventually wound up sleeping as much as an additional 1.25 hours per night more than their non-exercising counterparts. If you're not a regular exerciser and you're looking for a way to improve your sleep, starting a routine of moderate physical activity is a great strategy. Just keep in mind that the effect may happen gradually, not all at once. This is how we think of exercise as applied to weight loss -- and we may need to think of exercise in relation to sleep the same way.
For those already exercising, terrific! Your regular workouts are helping to protect the quality of your sleep. This study shows how your sleep can protect and enhance your workouts. You can strengthen your exercise regimen by getting a good night's rest. That's something to think about before staying up into the wee hours to work or watch late-night television.
As we so often learn, there is no magic bullet or quick fix to solve sleep problems. But when it comes to sleep and exercise, there is a significant benefit to be gained by sticking with a regular routine, and allowing the benefits to develop gradually. Slow and steady wins the race, in this case.
Michael J. Breus, PhD
The Sleep Doctor®
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