Exercise and Sleep

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Does exercise make it easier or harder to get to sleep? As in so many things involving sleep, the answer is both.

More often than not, exercise is good for your health and improves sleep quality. Sometimes it decreases sleep latency (e.g. you get to sleep faster) and increases sleep efficiency (e.g. you won’t be awake so much in bed). Some people are not healthy enough for exercise (check with your doctor) and even in people who are, heavy exercise sometimes results in middle-of-the-night awakenings. These might be due to hyperarousal (hard to relax) and/or increased adrenaline levels during the night following aerobic exercise. Increased body heat could also make it difficult to sleep.

Light aerobic exercise and anaerobic exercise such as lifting weights almost always increases sleep quality. If you are really interested in how exercise affects your sleep and how different types of exercise make you feel later that night, we encourage you to keep a sleep diary. Just a few data points may give you some insight about the type, intensity, and duration of exercise can help you.

Exercise before bed

The federal government (National Institute of Health) says 5 to 6 hours before bed exercise should be avoided during this time. This is intended as a very general guideline. The actual time differs from person to person. Strenuous exercise can make you sleepy. Lifting weights, for instance, when you haven’t been lifting in a while, makes most people sleepy.

Why should exercise make it easier to get to sleep or make the quality of sleep better? Is this a product of the “restorative” function of sleep – better rest? If so, that is thought to be a minor reason. Your muscles can rest while you are awake sitting on the couch watching television. it enhances/reinforces swings in your daily cycle, with increases in blood pressure, metabolic activity, and overall feeling of being alive. The “up” of exercise makes the “down” the following night feel lower and mitigates the feeling of hyperarousal that might cause insomnia.

Both aerobic and anaerobic exercise stimulate release or more growth hormone during the following night. Interestingly, it has been shown that the diminishing returns happen sooner with anaerobic exercise than with aerobic: i.e. if you increase the duration of your run you increase the boost in hormone release more than if you increase the duration of your weight-lifting session.

A study in India looked at the effect of exercise on sleep quality in elderly people. It concluded both anaerorbic and aeronic exercise promoted sleep quality, and that aerobic exercise was better.

Exercise is like a warm bath in that both are skeep hygiene/lifestyle choices that can make sleep better and which do not involve drugs. Why should a bath help with sleep? The bath (even in warm water) lowers body temperature and thereby signals the body to start sleeping in the evening – in conjunction with the circadian cycle.. But doesn’t warm bath water increase body temperature? No. Even a warm bath is cooler than body temperature. Further, after you exit the bathtub evaporation of residual water carries away heat and cools down your body.

Exercise and Sleep

You might hear or read statements like “getting exercise helps you sleep better”.  Like most simple statements about sleep physiology it is too simplistic to be always true.  But we can say it is mostly true.  In some situations exercise may disrupt sleep, but in other situations it will make you sleep sounder and reduce sleep latency.

In fact, starting an exercise program is often recommended as an approach to insomnia for people who want to avoid medicines.  Getting tired from exercise may somewhat assist people in falling asleep.  It is possible to rest the skeletal muscles without sleep, of course, but athletes who train at a high level often report a desire to sleep after a workout.  The average person doesn’t exercise that hard.

Science

These are anecdotes.  More formal study of the question has failed to find a strong connection between exercise and sleep quality and duration.  Researchers at the University of California at San Diego examined sleep and exercise diaries of college students and found “These results fail to support epidemiological data on the value of exercise for sleep, but are consistent with experimental evidence showing only modest effects of exercise on sleep.”

In a journal article called “Epidemiology of exercise and sleep” researchers from the University of South Carolina concluded “experimental evidence has found acute and chronic exercise to exert only modest effects on subsequent sleep.”

There it is some evidence that exercise may be a placebo when it comes to sleep latency.  By exercising, people think they will sleep better, and by thinking they will sleep better, they actually do sleep better.

When seniors participate in mild physical exercise they get more slow wave sleep.  Given the decline in deep sleep as we age, this is welcome news.

Some people seem to sleep better after exercise and some worse.  Not only does the effect vary from individual to individual, it varies with the time of day, length of time between exercise and bed, intensity of exercise, food and drink consumed, and fitness level. Attempts to draw generalizations amount the relationship between sleep and exercise have been thwarted by this observation.

A meta-study back in the 90s found that for the population as a whole, exercise improves the metrics of sleep quality.  The amount of deep sleep, amount of REM sleep, and total sleep time all tend to increase with exercise, sleep latency tends and fragmentation tend to fall. Other older studies had suggested no increase in slow-wave sleep;

A German study of children found that moderate exercise did not substantially change sleep architecture, but intense exercise shifts sleep from light sleep to deep sleep. (http://www.ncbi.nlm.nih.gov/pubmed/17644426)  REM sleep time did not appear to be affected by exercise.

There have been some speculation that the increased body heat from exercise may disrupt the sleep cycle.  The body’s thermoregulation process and the sleep cycle are connected.

Exercise in the few hours before bed also makes it difficult to get to sleep for many. One of the principles of sleep hygiene is avoiding rigorous exercise during the evening.

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