Getting a good night’s rest is important for so many aspects of our lives including our overall sense of wellbeing. The fact that we spend on average 33% of our lives sleeping is an indicator that sleep must serve a very important purpose. Not surprisingly, research has shown that a variety of physiological processes occur during this unconscious state. During sleep, for example, our musculoskeletal, immune and nervous systems go through a process of restoration. Additionally, our brains go through a process of neurochemical clearance and importantly, memories are formed – a process termed memory consolidation. Indeed, optimal health requires good and consistent sleep habits.
Unfortunately, lack of sleep is a serious public health concern with approximately 60 million Americans experiencing sleep difficulties (Centers for Disease Control and Prevention). People who experience sleep problems report issues with concentration, learning and memory, work or volunteer responsibilities, driving or taking public transit, tending to financial affairs, and engaging in things that they enjoy like hobbies. Additionally, individuals who do not get enough sleep are more likely to suffer from other chronic health issues such as hypertension, diabetes, depression, obesity and cancer. Fortunately, we can do several things to help us sleep better including having a regular sleep schedule (including sleep and wake times) and avoiding alcohol, nicotine and other drugs as well as large meals before bedtime. Another behavioral intervention to help us improve our sleep is to incorporate exercise into our daily lifestyle.
Much research has been done to investigate the relationship between exercise and sleep, and studies have shown that if you exercise, your self-reported sleep quality is much improved (Sherrill et al., 1998; Dzierzewski et al., 2014). Meta-analyses are systematic reviews that combine data from multiple studies to develop a single conclusion about a particular topic. Two meta-analyses that together examined 104 studies looking at the effect of exercise on sleep determined that acute exercise significantly improved a variety of sleep measures.
Specifically, exercise increases total sleep time by decreasing the time it takes to fall asleep, enhancing the efficiency of sleep (that is, how much time you actually sleep while laying down in bed), and delaying the wake time after sleep onset (Youngstedt et al., 1997; Kredlow et al., 2015). The most beneficial effects were seen when exercise took place 4 to 8 hours before bedtime. However, no need to worry if you prefer to exercise late at night, as exercising closer to bedtime did not disturb overall sleep quality.
Electroencephalography (EEG) is a non-invasive technique used to record activity of large groups of neurons in the cortex of humans, and neuroscientists have used this technique to record brain activity during sleep. When we sleep, our brains go through five different stages of sleep, stage I, II, III, IV and REM (rapid eye movement) sleep. Each sleep stage is characterized by rhythmic, wave-like patterns (like a sine wave) that have particular frequencies and amplitudes associated with them. As we descend through the stages of sleep into deeper sleep, the pattern of activity becomes slower (see the attached image). Interestingly, during REM sleep, which is the period of time when we dream, the activity patterns mimic brain activity during wakefulness.
Along with improving behavioral measures of sleep, exercise has been shown to improve the brain patterns associated with sleep (Youngstedt et al., 1997). As EEG sleep studies in humans are quite labor intensive, these kinds of studies have also been conducted in rodents. In one study, rodents were assigned to run, walk or remain sedentary for 45 minutes during their waking hours (Gambelunghe, 2001). Brain activity was then recorded while they slept. Compared to sedentary rodents, walkers and runners had an enhanced propensity to fall asleep. Additionally, this behavioral improvement in sleep was accompanied by enhanced duration of both slow wave sleep (occurs during stage III and IV) and REM sleep.
A variety of hypotheses have been put forth as to why exercise improves sleep. For example, exercise may improve sleep quality because it alters a variety of physiological and psychological factors including body temperature, metabolic rate, heart rate, heart rate variability, fatigue, mood and anxiety (Uchida et al., 2012). Other more molecular-based hypotheses suggest that exercise improves sleep because of changes in growth or immune factors such as interleukin-1, interleukin-6, and tumor necrosis factor-α, as these factors increase after bouts of exercise and have been shown to regulate the sleep-wake cycle.
Much more research is required to understand the exact mechanisms underlying exercise-induced sleep improvements. This work, however, highlights the idea that future studies should take these results into consideration as sleep improvement may be one of the reasons why chronic exercise improves other behaviors such as cognitive function and mood.
Related Article: 7 Tips To Get You Sleeping Again
Centers for Disease Control and Prevention (2015). Insufficient sleep is a public health problem. http://www.cdc.gov/features/dssleep/
Dzierzewski, J. M., Buman, M. P., Giacobbi, P. R., Roberts, B. L., Aiken‐Morgan, A. T., Marsiske, M., & McCrae, C. S. (2014). Exercise and sleep in community‐dwelling older adults: evidence for a reciprocal relationship.Journal of sleep research, 23(1), 61-68.
Gambelunghe, C. R. I. S. T. I. A. N. A., Rossi, R. U. G. G. E. R. O., Mariucci, G. I. U. S. E. P. P. I. N. A., Tantucci, M., & Ambrosini, M. V. (2001). Effects of light physical exercise on sleep regulation in rats. Medicine and science in sports and exercise, 33(1), 57-60.
Kredlow, M. A., Capozzoli, M. C., Hearon, B. A., Calkins, A. W., & Otto, M. W. (2015). The effects of physical activity on sleep: a meta-analytic review.Journal of behavioral medicine, 38(3), 427-449.
Sherrill, D. L., Kotchou, K., & Quan, S. F. (1998). Association of physical activity and human sleep disorders. Archives of internal medicine, 158(17), 1894-1898.
Uchida, S., Shioda, K., Morita, Y., Kubota, C., Ganeko, M., & Takeda, N. (2012). Exercise effects on sleep physiology. Frontiers in neurology, 3, 48.
Youngstedt, S. D., O’Connor, P. J., & Dishman, R. K. (1997). The effects of acute exercise on sleep: a quantitative syntesis. Sleep, 20, 103-14.
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