Exercise and sleep are two vital parts of a healthy lifestyle. In general, we know that working up a sweat and getting rest go hand-in-hand: Healthy sleep patterns often predict higher levels of activity. And, more and more, athletes and other people whose lives revolve around being in shape are making rest a priority. But, as a new review paper makes clear, the relationship between these two good-for-you behaviors isn't that straightforward.
Researchers from UCLA's Geffen School of Medicine and the VA Greater Los Angeles Healthcare System poured over sleep-and-exercise studies published between 2013 and 2017. Based on their analysis of 34 studies — including public health surveys and experimental research — they found that the degree to which exercise predicted better sleep depended on factors including the type of exercise in question, the reason for exercising and the age of participants. In other words, sleep and exercise do influence each other, but not always in a predictable or consistent way. Here are seven takeaways from the paper to help you understand how moving your body today could help you sleep like a champ tonight.
Sleep comes to those who exercise for pleasure
It's important to examine not only how much you exercise but also why you do it. In one study, participants who got the best sleep reported getting (a lot of) exercise from leisure activities. People who were active for other reasons, e.g., due to occupational demands, reported worse sleep, as did people who didn't exercise at all. So, even if your job already keeps you on your feet, it's still worth your while to carve out time for exercise you enjoy.
Timing is secondary
No sleep-and-exercise discussion is complete without dipping back into the time-of-day debate. The big question is: Does working out at night leave you too over-stimulated to get solid rest? And if it does, is it better to exercise at night or skip it all together? We don't have any definitive answers yet, but the review paper suggests that sunrise and sunset exercise both improve sleep — just in slightly different ways.
In one study, researchers looked at various sleep and physiological measures (e.g., melatonin levels, rectal temperature, and EEG activity) and determined that exercising early in the day improves the quality of nighttime sleep. But, in another study, exercising 90 minutes before bedtime was associated with increased deep sleep. And a third study found that, regardless of the time of day, resistance training improved sleep quality: Morning training reduced the amount of time it took for participants to fall asleep (a good thing), whereas nighttime training reduced the number of times participants woke up after they fell asleep (also a good thing). In summary? Don't be afraid of working out after work.
Lie yourself to sleep
Maybe you're not running six-minute miles or toning your core like an Instagram fitness model. But, regardless of what you're actually doing in the gym, believing that you're pushing your body to its limits could help you fall into a deeper sleep than usual. In the same study that said it's cool to get sweaty 90 minutes before bed, participants who perceived their workouts as being really hard exhibited increased deep sleep. Participants who reported lower levels of self-perceived exertion did not get the same deep-sleep upgrade. Sleeping is believing.
Get fit, get sleep
Exercise probably improves sleep for a number of reasons — the biological mechanisms underlying the relationship aren't fully understood yet, but the literature suggests that working out is beneficial to sleep in large part because it enhances fitness and protects against metabolic disease. For one thing, the link between exercise and sleep bears out more consistently for regular exercise than one-time workouts. This suggests that the longer-term health effects of exercise are the driving factor behind resulting sleep changes. Exercise also appears to affect sleep the most for people who aren't in great shape. In one study, participants had to complete a 15-week exercise regimen. The only participants who exhibited markedly changed sleep patterns were those who'd been classified as overweight or obese at the outset of the study and shed weight during it.
If you're already in great shape, more exercise probably won't help you sleep
(Take a closer look at your diet instead.) Athletes aren't immune to sleep problems. But they're less likely than other people to reap the rest-enhancing benefits of exercise. This is probably because they're already working out at maximum capacity. If the uber-fit can't sleep because, let's say, they're dealing with performance anxiety or jet lag from non-stop travel, ramping up their training schedule probably isn't the answer. Instead, poorly slept athletes could try changing their diets by increasing their protein intake, avoiding high-fat foods, and eating tryptophan-rich foods like pumpkin seeds.
Exercise might make the biggest difference for older people
Exercise doesn't have the same impact on sleep for young and middle-aged adults as it does for mature adults. Studies on older adults have linked both routine exercise regimens and single, intense workout sessions to improved sleep. Age and sex, researchers surmise, changes the way exercise and sleep interact.
The mind matters, too
Yes, physical fitness is a big factor in the exercise-sleep link. But the mental effects of exercise also seem to play a role. In one study on older adults, both intense aerobic exercise and mind-body exercise (yoga, Tai Chi) lead to improved objective sleep, as measured by actigraphy trackers (e.g., fitbit). But participants in the mind-body group reported significant improvements in sleep, mood, and mental health. The aerobic exercisers didn't. The emphasis on relaxation and emotional regulation in mind-body exercise might make it especially useful for people whose sleep issues are rooted in anxiety. And combining mind-body, aerobic, and strength training might make exercise a particularly effective weapon against poor sleep.