Q:CAN EXERCISE HELP OR HINDER GETTING A GOOD NIGHT’S SLEEP? DOES THE TIMING OF EXERCISE RELATIVE TO BEDTIME MATTER?
A good night’s sleep can be elusive. Within the United States, chronic sleep loss or sleep disorders may impact up to 70 million people (5); see the Figure for prevalence of insufficient rest or sleep among adults in each state. This translates to significant health care expenses (∼$16 billion annually) and lost productivity (∼$50 billion) (5). Daytime sleepiness is reported by more than one third of adults who report experiencing problems with work, driving, and social functioning as a result (5). Approximately half of older adults also complain of difficulty sleeping; this potentially is a function of various factors observed with aging, including illness, medication use, and changes in the circadian clock (10).
Total sleep requirements vary widely for various species, for example, 19.9 hours per day for brown bats compared with only 1.9 hours per day for giraffes; common household pets fall between these two extremes, with 12.1 hours per day for cats and 10.6 hours per day for dogs (6). Humans vary in their sleep requirements as well; infants need an average of 16 hours per day and adolescents 9 hours per day (6). Adults seem to need between 7 and 8 hours per night to be well rested (5). However, the average American adult does not achieve even 7 hours per night — in contrast to the 9 hours of sleep reported in 1910 (5). Individual sleep requirements vary depending on a number of factors, including genetics, physiology, age, sex, and previous amount of sleep (1). Quality sleep has been described as “being easy to fall into sleep and wake up, and when sleep is continuous and long enough” (4).
Does sleep really matter with regard to health and daily living? The answer seems to be a resounding YES. The National Heart, Lung, and Blood Institute (NHLBI) highlights a number of benefits in the publication Your Guide to Healthy Sleep, available as a free download at http://www.nhlbi.nih.gov/health/public/sleep/ (5). For a sample of some of the benefits noted by the NHLBI, see Box 1. For additional helpful resources on sleep, see Box 3.
SLEEP AND EXERCISE
Regular exercise is one of the common tips for achieving a good night’s sleep (8). For 10 healthy sleep tips from the National Sleep Foundation, see http://www.sleepfoundation.org/article/sleep-topics/healthy-sleep-tips (8). In a recent mini-review, researchers underscore the health and fitness benefits of exercise while trying to determine the potential impact of exercise on sleep physiology (11). Meta-analyses of chronic exercise studies seem to support shorter sleep onset latency, less time awake after sleep onset, and longer total sleep time (11). In another review article, researchers proposed that regular aerobic or resistance training was helpful in improving sleep quality in adults older than 40 years; this included a perceived reduction in time to fall asleep and reduced use of medication for insomnia (12).
If exercise is beneficial in improving sleep, the next question that follows is “how?” Various mechanisms by which exercise could promote sleep include (13):
- Anxiety reduction: Anxiety is associated with disturbed sleep and because exercise has the potential to reduce anxiety, exercise may promote sleep.
- Antidepressant effects: Depression and disturbed sleep are related, and thus the antidepressant effects of exercise may be beneficial to sleep.
- Thermogenic effect: Temperature downregulation associated with sleep onset may be promoted by heat acclimation associated with exercise.
Although exercise seems to have a beneficial effect on chronic insomnia, details on the optimal amount, type, and timing of exercise are still areas in need of additional research (3).
Sleep hygiene recommendations often discourage exercise close to bedtime. However, new survey results suggest exercise at any time of day may be better than no exercise at all (9). In 2013, the National Sleep Foundation’s annual Sleep in America® poll focused on the relationship between physical activity, exercise, and sleep, with the bottom line neatly summarized in this statement: “Data from the 2013 Sleep in America® poll overwhelmingly support the proposition that ‘Exercise is good for sleep’” (7). Survey research such as the NationalSleep Foundation 2013 poll can demonstrate a relationship between good sleep and exercise but, by the nature of the study, cannot state definitively a cause-and-effect relationship (i.e., does exercise cause a good night’s sleep or does a good night’s sleep help to increase one’s amount of exercise) and does not address other factors, such as health, that could impact both physical activity level and sleep. Regardless, the 2013 poll results provide insight into the positive relationship between exercise and sleep (9). For more information, see Box 4, or for the complete report (7), see http://www.sleepfoundation.org/2013poll.
In support of the findings of the National Sleep Foundation poll, consider the results of a study related to vigorous exercise before bedtime. Eleven physically fit young adults were monitored in a sleep laboratory under two conditions: 1) after an incremental cycle ergometer exercise bout until exhaustion (exercise duration approximately was 35 minutes and occurred 2 to 2.5 hours before bedtime) or 2) control condition without any exercise (4). After the exercise bout, researchers found a greater proportion of non-rapid eye movement sleep and no difference compared with the control condition for subjective sleep quality (4). Heart rate was higher for the first 3 hours of sleep after the exercise bout but did not seem to disturb sleep (4).
Researchers acknowledge the complexity related to recovery during sleep, including potential impact of various physiological and psychological aspects (4). For example, some researchers have raised the question of the impact of fitness and the possibility that the sympathetic nervous system of fit individuals may be able to recover more quickly from the increase that occurs with exercise (14). Others have questioned if fitness level and perceived physical activity might play a role in sleep (i.e., cognitive processes such as the role of beliefs, perceptions, and expectations related to the sleep) (2). Another factor to consider when reviewing research is the population studied; research with good sleepers may not have shown significant sleep improvements (as there is little room to improve) whereas studies including those with insomnia have more encouraging results (13).
Sleep is an important and dynamic part of one’s daily routine. Researchers continue to examine factors that influence sleep and the influence that sleep quality and quantity may have on health and daily function. Although many questions remain relative to the effect of exercise on the physiology of sleep, exercise does not seem to impact negatively, and may help to promote, achieving a good night’s sleep. With a potential sleep benefit, along with the myriad of other health benefits from a physically activity lifestyle — one can see a real win-win situation.
2. Gerber M, Brand S, Holsboer-Trachsler E, Puhse U. Fitness and exercise as correlates of sleep complaints: is it all in our minds? Med. Sci. Sports Exerc. 2010; 42 (5): 893–901.
4. Myllymäki T, Kyröläinen H, Savolainen K, Hokka L, Jakonen R, Juuti T, Martinmäki K, Kaartinen J, Kinnunen ML, Rusko H. Effects of vigorous late-night exercise on sleep quality and cardiac autonomic activity. J Sleep Res. 2011; 20: 146–153. [cited 2013 March 27]. Available from: http://www.ncbi.nlm.nih.gov/pubmed/20673290.
5. National Heart, Lung, and Blood Institute; U.S. Department of Health & Human Services; National Institutes of Health. Your Guide to Healthy Sleep. NIH Publication No. 11-5271. Bethesda (MD): National Heart Lung and Blood Institute; 2011. [cited 2013 April 1]. Available from: http://www.nhlbi.nih.gov/health/public/sleep/healthy_sleep.htm.
7. National Sleep Foundation. 2013 Sleep in America Poll: Exercise and Sleep. Arlington (VA): National Sleep Foundation; 2013. [cited 2013 April 1]. Available from: http://www.sleepfoundation.org/2013poll.
12. Yang P-Y, Ho K-H, Chen H-C, Chien M-Y. Exercise training improves sleep quality in middle-aged and older adults with sleep problems: a systematic review. J Physiother. 2002; 58: 157–63.
13. Youngstedt SD. Effects of exercise on sleep. Clin Sports Med. 2005; 24: 355–65.
14. Youngstedt SD, Kripki DF, Elliott JA. Is sleep disturbed by vigorous late-night exercise? Med Sci Sports Exerc. 1999; 31 (6): 864–9.