Physical Exercise & Sleep: A (very small) Review
In today’s society, where sleeping time averages have been constantly diminishing since the invention of the light bulb (Sleep in America Poll, 2003) and stressful environments (Myllymaki, T et al. 2011), it has been reported that 7 out of 10 Americans indicate having frequent sleep difficulties (Sleep in America Poll, 2003). Considering the importance of sleep for human physiology (Taylor, 2001)(Buguet & Lonsorfer, 1987), it was of interest to investigate the effect of physical exercise on the quality of sleep in healthy individuals, considering the advantageous position health clinicians find themselves to promote and recommend physical exercise.
Importance of sleep
From a physiological aspect, adequate sleep may be important as a restorative mechanism, increasing anabolic processes, important to counter balance the daytime demands characterized by catabolic processes (Taylor, 2001)(Buguet & Lonsorfer, 1987). In fact, as reported by Sigurdson and Avas (2007), sleep loss may be associated with severe long-term problematic such as cardio-vascular diseases, type-2 diabetes, obesity, clinical depression and an increase in all-cause mortality (Myllymaki, T. et al., 2011).
In addition to physiological benefits of sleep, psychological well-being is also associated with adequate sleep (Myllymaki et al., 2011). Daytime sleepiness linked to poor sleep quality (Myllymaki et al., 2011) may also lead to an economic burden due to work absence and decrease in productivity, as reported by Daley et al. (2009) (Myllymaki et al., 2011).
Objective measurements of sleep
Electroencephalogram (measurement of brain wave activity), electromyogram (measurement of muscular activity), electrooculogram (measurement of ocular movement activity) are often grouped together in what is called a polysomnogram which records a wide scope of biophysiological variables observable during sleep (Myllymèaki et al., 2011)(Myllymèaki et al., 2012)(Montgomery, Trinder, Paxton 1982)(Trinder, Stevenson, Paxton, Montgomery, 1982)(Trinder, Buck, Paxton, Montgomery, Bowling, 1982)(Flausino, Da, Queiroz, Tufik, Mello, 2012)(Shapiro et al., 1984). Lastly, actigraphy (measurement of human activity and rest cycles) and heart rate variability (assessment of the autonomous nervous system) are used as additional non-invasive methods (Flausino, Da, Queiroz, Tufik, Mello, 2012)(Myllymèaki et al., 2011)(Myllymèaki et al., 2012).
Subjective measurements of sleep
Assessed through self-reported questionnaires, they investigate different components of sleep such as sleep quality, sleep latency, sleep duration, sleep efficiency, sleep disturbances, use of sleep medication, tiredness, and daytime dysfunction (Myllymèaki et al., 2012)(Sleep in America Poll, 2003)(Mensink, Loose, Oomen, 1997).
Chronic exercise and sleep
When comparing fit individuals, to unfit individuals, it was established that the fitness level influenced sleep cycle length characterized by the time lapse between the 3 phases of non rapid eye movement (NREM) and the single phase of rapid eye movement (REM) (Trinder, Stevenson, Paxton, Montgomery, 1982)(Montgomery, Trinder, Paxton 1982). This observation seems to be related to metabolic rate, where metabolic rate is inversely proportional to sleep cycle length. Indeed, fit individuals are known to possess higher metabolic rate known to be a normal physiological adaptation to exercise stress (Trinder, Stevenson, Paxton, Montgomery, 1982).
Furthermore, slow wave sleep (SWS) that occurs during the third phase of NREM sleep, has been observed to increase in a fit population (Trinder, Buck, Paxton, Montgomery, Bowling, 1982)(Montgomery, Trinder, Paxton 1982)(Shapiro et al., 1984). This phase has been said to be the most restorative phase of sleep, and thus, improve its quality (Trinder, Buck, Paxton, Montgomery, Bowling, 1982)(Shapiro et al., 1984).
Lastly, fit individuals demonstrated longer sleep duration and an increase in the ability to fall asleep (Montgomery, Trinder, Paxton 1982) when compared ton their untrained counter-parts. These observations perdure in time, even in periods of reduced exercise levels, demonstrating long-term benefits of exercise on sleep (Montgomery, Trinder, Paxton 1982) possibly explained by the apparent effect of fitness and metabolic rate on sleep cycle length (Trinder, Stevenson, Paxton, Montgomery, 1982)(Montgomery, Trinder, Paxton 1982).
Acute exercise and sleep
It has been observed that acute bouts of physical activity does not affect sleep cycle length, a finding suggesting that sporadic physical activity may have no objective effect on sleep (Trinder, Stevenson, Paxton, Montgomery, 1982)(Myllymèaki et al., 2012).
Regarding the period of day when exercise is performed, it is commonly accepted that exercise before sleep may disturb it’s quality, but results from a variety of studies suggest that it has no effect or can account for a slight increase in sleep quality. Myllymèaki et al (2011) demonstrated through polysomnography that high intensity exercise performed before going to bed (2-2.5 h) caused decrease in sleep onset latency, defined as the time taken to fall asleep. It is proposed that an increase in body temperature caused by physical exercise has greater effect on the ability to fall asleep then the sleep-disturbance influence generated by physical exercise, such as the secretion of specific hormones (Myllymèaki et al., 2011). In addition to improving the ability to fall asleep, it seems that acute exercise before bed-time increase sleep efficiency, increase REM sleep latency and decrease awake time after sleep onset (Flausino, Da, Queiroz, Tufik, Mello, 2012).
Exercise and subjective perception of sleep
Self-reports about sleeping habits demonstrate that exercise is perceived as being a helpful habit to a good sleep (Sleep in America Poll, 2003). Furthermore, an epidemiological study has concluded similar results where regular physical activity enhanced the perception of sleep quality (Mensink, Loose, Oomen, 1997). As of exercise before bedtime, subjective sleep quality was not affected (Myllymèaki et al., 2012).
It is important to note that this literature review posses many limitations. Indeed, considering the undeniable subjectivity of sleep, it would have been important to consult primary sources where both objective and subjective data were collected, to better represent the assessment of sleep quality.
As the literature review progressed, it became clear that the research question was too broad. Precision regarding the type of exercise (e.g. chronic, acute, aerobic, strength training) and sleep (e.g. amount of SWS, sleep length, sleep cycle length) would have allowed a better understanding of the current knowledge on physical exercise and sleep.
Conclusion (Lazy reader? Read THIS!)
Ultimately, the major themes of this literature review tend to show that chronic amounts of physical activity have more effect on sleep than acute amounts of exercise. In fit individuals, benefits of exercise on sleep quality last over-time and may be explained by increase in metabolic rate. Findings also seem to contradict common thought that sleep before bedtime is negative considering the neutral or positive effect on sleep that some study demonstrated. From a subjective point of view, exercise as a whole seems to positively influence quality of sleep.
These conclusions are interesting for health clinicians considering that the literature is showing a positive influence of exercise on sleep, although the details and mechanisms behind these findings must be investigated further.
It would be of great interest to now investigate the exact mechanisms behind the benefits of physical activity and sleep, in the purpose to better control, monitor and recommend physical exercise to patients who whish to ameliorate their sleep quality.
Written by Antoine Del Bello
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Flausino, N. H., Da, S. P. J. M., Queiroz, S. S., Tufik, S., & Mello, M. T. (2012). Physical exercise performed before bedtime improves the sleep pattern of healthy young good sleepers. Psychophysiology, 49, 2, 186-192.
Mensink, G. B. M., Loose, N., & Oomen, C. M. (1997). Physical activity and its association with other lifestyle factors. European Journal of Epidemiology, 13, 7, 771.
Montgomery I, Trinder J, Paxton SJ. (1982). Energy expenditure and total sleep time: effect of physical exercise. Sleep, 5, 159-169
Myllymaki, T., Kyrolainen, H., Hokka, L., Juuti, T., Martinmaki, K., Kinnunen, M.-L., Rusko, H., Kaartinen, J. (2011). Effects of vigorous late-night exercise on sleep quality and cardiac autonomic activity. Journal of Sleep Research, 20, 146-153.
Myllymèaki, T., Rusko, H., Syvèaoja, H., Juuti, T., Kinnunen, M.-L., & Kyrèolèainen, H. (2012). Effects of exercise intensity and duration on nocturnal heart rate variability and sleep quality. European Journal of Applied Physiology, 112, 3, 801-809.
National Sleep Foundation. (2003). Sleep in America Poll. Washington, DC: National Sleep Foundation, 2003.
Shapiro, C. M., Warren, P. M., Trinder, J., Paxton, S. J., Oswald, I., Flenley, D. C., & Catterall, J. R. (1984). Fitness facilitates sleep. European Journal of Applied Physiology and Occupational Physiology, 53, 1, 1-4.
Taylor, S. R. (2001). The influence of exercise on sleep quality. International Sportmed Journal, 2, 3, 1-10.
Trinder, J., Bruck, D., Paxton, S. J., Montgomery, I., & Bowling, A. (1982). Physical fitness, exercise, age and human sleep. Australian Journal of Psychology, 34, 2, 131-138.
Trinder, J., Stevenson, J., Paxton, S. J., & Montgomery, I. (1982). Physical Fitness, Exercise, and REM Sleep Cycle Length. Psychophysiology, 19, 1, 89-93.