The relationship between exercise and sleep has been extensively investigated over the years. Previous studies have noted that proper exercise can alleviate sleep-related problems and help you get an adequate amount of rest. Recent research also suggests insufficient or poor-quality sleep can lead to lower levels of physical activity the following day.
For these reasons, experts today believe sleep and exercise have a bidirectional relationship. In other words, optimizing your exercise routine can potentially help you sleep better and getting an adequate amount of sleep may promote healthier physical activity levels during the day.
How Does Exercise Impact Sleep?
There are many benefits to exercising regularly. These include a lower risk of diseases like cancer and diabetes, improved physical function, and a higher quality of life. Exercising can also benefit certain groups. For example, pregnant women who engage in routine physical activity are less likely to gain an excessive amount of weight or experience postpartum depression, and elderly people who exercise are at lower risk of being injured during a fall.
Exercising also improves sleep for many people. Specifically, moderate-to-vigorous exercise can increase sleep quality for adults by reducing sleep onset – or the time it takes to fall asleep – and decrease the amount of time they lie awake in bed during the night. Additionally, physical activity can help alleviate daytime sleepiness and, for some people, reduce the need for sleep medications.
Exercise can also improve sleep in indirect ways. For instance, moderate-to-vigorous physical activity can decrease the risk of excessive weight gain, which in turn makes that person less likely to experience symptoms of obstructive sleep apnea (OSA). Roughly 60% of moderate to severe OSA cases have been attributed to obesity.
Numerous surveys have explored sleep and exercise habits among adults. These include the National Sleep Foundation’s 2003 Sleep in America poll, which surveyed adults between the ages of 55 and 84.
Among that survey’s respondents, about 52% said they exercised three or more times per week and 24% said they exercised less than once a week. Respondents in the latter group were more likely to sleep less than six hours per night, experience fair or poor sleep quality, struggle with falling and staying asleep, and receiving a diagnosis for a sleep disorder such as insomnia, sleep apnea, or restless legs syndrome.
The 2013 Sleep in America poll, which surveyed adults between the ages of 23 and 60 and focused on “Exercise and Sleep,” produced similar results. Roughly 76-83% of respondents who engage in light, moderate, or vigorous exercise reported very good or fairly good sleep quality. For those who did not exercise, this figure dropped to 56%. People who exercised were also more likely to get more sleep than needed during the work week.
Similar studies and surveys have focused on the effects of exercise for subjects in other demographic groups. One study profiled college students during their examination periods and found that exercise and physical activity can reduce test-related stress. Another study noted that sleep and exercise are “dynamically related” for community-dwelling older adults. Additionally, a third study found that regular, mostly aerobic exercise reduced symptoms for people with OSA, even if they didn’t lose any weight in the process.
Compared to exercise, jobs involving manual labor may not provide the same relief for sleep problems. One reason for this is that many laborious jobs often lead to musculoskeletal aches and pains that can negatively impact sleep. Moreover, manual labor involving long working hours can increase an employee’s risk for stress and fatigue.
Is It Harmful to Exercise Before Bed?
The question of whether exercise in the hours before bedtime contributes to poor-quality sleep has been hotly debated over the years. Traditional sleep hygiene dictates that intensive exercise during the three-hour period leading up to sleep can negatively impact sleep because it can increase your heart rate, body temperature, and adrenaline levels. On the other hand, some studies have noted exercising before bed may not produce any negative effects.
One survey found that the majority of people who exercise at 8 p.m. or later fall asleep quickly, experience an adequate amount of deep sleep, and wake up feeling well-rested. Respondents who exercise between 4 and 8 p.m. reported similar percentages for these categories, suggesting late-night exercise may actually benefit some people.
Other studies have yielded similar results. In one, subjects who exercised in the evening reported more slow-wave sleep and increased latency for rapid eye movement sleep compared to the control group, as well as less stage 1 (or light) sleep. However, researchers also noted that a higher core temperature – which can occur after intensive workouts – was associated with lower sleep efficiency and more time awake after sleep onset. So while exercising before bedtime may not be inherently harmful, vigorous workouts in the hour leading up to bed can affect sleep efficiency and total sleep time.
That said, some surveys have found the vast majority of people do not exercise in the hour before bedtime. One example is the National Sleep Foundation’s 2005 Sleep in America poll, which surveyed adults 18 and older. Of these respondents, 4% said they exercised within an hour of bedtime on a nightly basis, 7% said they did so a few nights a week, and 5% said they exercised before bed a few nights per month. The remaining respondents either rarely or never exercised an hour before bedtime, or refused to answer.
Since survey results among people who exercise late at night have been variable, you should base your exercise times and intensity on what best suits your sleep schedule. Certain exercises may be more beneficial for sleep than others. These include yoga, light stretching, and breathing exercises.
How Does Sleep Impact Exercise?
The role sleep plays in our physical activity levels has not been studied as thoroughly, and much of the research has focused on differences in physical activity between people with sleep disorders and healthy individuals.
However, most of these studies have concluded that those who experience poor sleep are less active than those with healthy sleep cycles. In particular, people with certain sleep disorders are not as likely to exercise during the day. Adults with insomnia tend to be less active than those without insomnia. The same is true for people with OSA and other types of sleep-disordered breathing, though excess weight may also be a factor for this population.
Some studies have noted that nightly shifts in sleep quality, latency, and efficiency can be used to predict physical activity levels. For example, one study found that a 30-minute increase in sleep onset was associated with a one-minute decrease in exercise duration the next day.
A person’s preference for morning or evening activity may also play a role. People who are early risers or “morning people” are more likely to engage in physical activity than those who sleep in or are more active in the evening. In fact, some studies have suggested that exercise can essentially alter one’s diurnal preference over time, and may even shift their circadian rhythms.
Although many studies to date have established a relationship between high-quality sleep and healthy physical activity levels, the research to date has not conclusively proven that better sleep leads to an increase in physical activity levels.
One series of studies noted that one to six months of continuous positive air pressure (CPAP) therapy – a first-line treatment for OSA – did not have any noticeable effect on a person’s physical activity levels, even though the therapy alleviated OSA symptoms and promoted better sleep. Another study explored the effect of CPAP therapy combined with modified eating habits. At the conclusion of this study, the subjects had successfully retooled their dietary patterns but had not adjusted their physical activity levels to a meaningful degree.
The takeaway here is that a good night’s sleep can help you feel well-rested and more motivated to exercise the following day, but healthy sleep alone may not be enough to spontaneously change how and how often you engage in physical activity.
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