Effects of Exercise on Sleep

Original Editor - Sai Kripa

Top Contributors - Sai Kripa, Pacifique Dusabeyezu, Kim Jackson and Sehriban Ozmen  

Introduction

Sleep is defined as a reversible behavioral state of perceptual disconnection from and impassiveness to the surroundings. It is usually divided into two sleep states, namely rapid eye movement (REM) sleep, non-rapid eye movement (NREM) sleep. While sleeping at night there is a sequential rotation occurs quite a lot of times (5 to 6 times) among these two sleep states. According to American sleep association, there are many sleep disorders that humans suffer from; including dyssomnias such as Sleep Apnea, Hypersomnia and Insomnia; Bruxism; parasomnias such as REM Behavior Disorder and sleepwalking, and circadian rhythm sleep disorders. Furthermore, sleep disorders are so common among individuals and it could lead to chronic sleep deprivation which is completely dangerous. There are numerous pharmacological interventions available to treat these sleep disorders, however one of the best non-pharmacological intervention approved by American Sleep Disorders Association regarding improving your sleep is considered to be Exercise, Wide epidemiological studies indicate that the general population recognizes the therapeutic and sleep promoting advantages of moderate to regular physical activity. Also, there are few researches that has been conducted on subjects to identify the effects of exercise upon sleep quality and quantity. Since exercise induces physical exhaustion, moreover its physiological and psychological calming effects are well known, it can be obvious to assume that exercise promotes sleep. 

 

Exercise and Insomnia

Two recent studies suggest improvement in sleep that has been performed to test the effect of exercise training among insomniacs. Guilleminault et al randomly allocated 3 separate 4-week therapies to 30 individuals (average age 44) who had psychophysiologic insomnia. The first set of intervention included sleep hygiene education, such as motivating the individuals to maintain a fixed sleep-wake schedule and to ignore daytime napping. The second set of intervention included sleep hygiene education and light therapy that involved individuals to sit in front of a bright light (3,000 lux) for 45 minutes beginning 5 minutes after awakening. The third set of intervention included sleep hygiene education and 45 minutes of brisk daily walking in the early evening. According to evidence, there has been an exercise-related improvement in sleep probably due to individual's exposure to outdoor light during exercise and at other times of the day. Apart from outdoor exposure, the improvement would have also been due to individual's different expectations for improved sleep associated with each protocol.

In another report, King et al randomly assigned 43 older people (age 50 to 76) with moderate sleep complaints to an exercise program for 16 weeks or to a waiting list control condition. During the day or early evening, the exercise group performed 30-40 minutes of moderate aerobic exercise 4 times per week. Based on sleep diaries and the Pittsburgh Sleep Quality Index, the exercise group showed considerably higher improvements in sleep. Nevertheless, on observing at these handful of evidences that have been performed suggest that exercise significantly improves the sleep of people with insomnia. 

Acute Exercise and Sleep

A recent meta-analysis of 38 studies carried out by Youngstedt et al examined the mean impact of acute exercise on sleep. Additionally, these studies pay attention exclusively on subjects who are good sleepers. Even the sleeping pills can have little effect on healthy sleepers. The small size of the results relating to exercise does not inherently undermine their meaning.

In all studies, sleep was assessed by polysomnography and the analysis concluded that:

• No effects on the amount of time it took to fall asleep;
• Statistically significant yet marginal improvement in overall sleep time (average 10 minutes) and slow-wave sleep time (average 4 minutes)
• Statistically significant but limited decrease in rapid eye movement ( REM) sleep (average 7 minutes), increases in the time for REM sleep to occur following sleep onset (average, 13 minutes).

Although the research focused on healthy sleepers, the results reveal nothing about the impact of acute exercise on sleep disorder sufferers. Furthermore, there are lack of evidence to prove the effects of acute exercise in such individuals.

Factors Influencing Exercise and Sleep

There are numerous factors that can potentially contribute to effects of sleep on exercise. It includes individual’s level of fitness, thermoregulation, duration of exercise, time of exercise, and light exposure. Examining such factors could facilitate us to know the mechanism by which exercise influences sleep and the parameter that most influence sleep.

• Fitness- Some researchers have hypothesized that the extreme, comprehensive exercise believed to be important for sleep enhancement can only be done by fit subjects. Since unfit subjects are unable to reach the exercise level that might be required for better sleep, the claim goes, exercise will profit them less than it would benefit fit individuals. Experimental evidence, however, suggests that fitness does not affect the effects of acute sleep exercise, and these findings are consistent with surveys indicating that exercise in the general population encourages sleep.

• Thermoregulation- The thermo-genic hypothesis, which posits that exercise enhances sleep by heating the body or brain, has been a widespread theory for the effects of exercise on sleep. This hypothesis is consistent with findings that passive body heating promotes slow-wave sleep via a hot tub or sauna. Neurophysiologic evidence also indicates an association in the anterior hypothalamus between heat loss and sleep processes that are triggered when the temperature is elevated. Therefore, exercise may work as a thermo-genic stimulus to enhance sleep. Since body temperature rises as a result of exercise intensity during exercise, the thermo-genic hypothesis indicates that the more intensive the exercise, the greater the increase in sleep. As individuals have a general habit of exercising at lower intensities which would also suggest that exercise would not benefit for most individuals sleep.

• Duration of exercise- Meta-analysis suggested that duration of exercise was considered to be one of the major factor modifying the influence of exercise on sleep. As the exercise duration increased beyond 1 hour a day, there was a steady rise in overall sleep time. Additional research is needed to clarify whether very prolonged exercise will improve overall sleep.

• Time of exercise- Performing intense exercise before bed time interrupts sleep is recognized to be a common belief among individuals. Recent evidence questions the supposition that sleep is disrupted by late-night exercise. Sleep was not adversely affected in aerobically fit subjects by a 1 hour bout of exercise at 60% VO2 max or by 3 hours of exercise at 70% VO2 max done 30 minutes prior to bed time. On the other hand, a population study found that exercise improved or had no effect on sleep for most individuals within 2 hours of bedtime.

• Light exposure- Insufficient exposure to bright light has been related to disrupted sleep. Conversely, exposure to bright light can cause rapid and drastic changes in sleep. Although the average adult receives just around 20 minutes of daily exposure to bright light-more than 2,500 lux-it is fair to believe that at least three times as much is obtained by people who exercise regularly outdoors. In view of the recent study suggesting that exposure to bright light could boost sleep more than exercise. It is important to examine this issue more carefully. The synergistic effects of exercise and bright light on sleep may be fascinating.

Anti-Depressant Effects

Anxiety is considered as one of the primary cause of insomnia, especially transitory, situational insomnia. Because exercise has shown to reduce psychophysiological and subjective anxiety indices, and anxiolytic therapeutic therapies have been successful for insomnia, it is possible that exercise by reducing anxiety can promote sleep. Chronic exercise may also promote sleep by its antidepressant effects. Acute exercise delays REM onset and decreases REM sleep overall. Vogel et al have argued that these REM effects are the mechanism by which all antidepressant treatments work.

Conclusion

Clearly there is a need for more studies to investigate the impact of exercise on sleep and to assess if they can be linked to exercise or related factors. Until such study findings are available a formal exercise prescription for sleep disorders is not warranted. However, physicians and scientists may also recommend exercising as a way to boost sleep. Based on epidemiological data and recent insomnia experimental research, the recommendations seem rational, particularly if exercise is part of an overall treatment regimen and indicates with the patient's understanding that it could yield little or no sleep improvement. Although exercise does not improve sleep, exercise can reduce overall mortality and morbidity.

Resource

The brain-changing benefits of exercise