How Much You Need to Exercise for Better Sleep, According to Experts

Ever notice how some workouts put you to sleep while others make you feel like someone switched out your vitamins for caffeine pills? You’re not going crazy. Exercise can significantly impact your sleep—for better or for worse—depending on how, and when, you work out.Unfortunately, the exercise-sleep relationship is not as straightforward as the internet’s sleepmaxxers might lead you to believe. While research has unlocked some valuable insights that you can start putting into practice later tonight, there’s still a lot we don’t know. "Part of what's vexing about this is we don't have the mechanism totally locked down,” says James Wyatt, PhD, clinical sleep disorder specialist at Rush University System for Health in Chicago."It's also important to caveat that, while the data is enormously helpful, there's so much intra-individual variability,” says Kristen Holmes, PhD, global head of human performance and principal scientist at Whoop. At the end of the day (literally), sleep is a complex chemical equation that differs to various degrees from person to person.But back to those valuable insights. From morning HIIT workouts that reset your circadian rhythm to an evening workout to hack your body’s natural cooling system, here are some of the best ways to use exercise to fall asleep faster, according to experts.Working out in general won’t make you fall asleep fasterExercise can certainly reduce the time it takes to fall asleep, but not for the reason that many wellness influencers would have you think—that is, by spurring your body’s natural production of adenosine, a sleep-inducing compound that is also a byproduct of exercise.Your body’s cells rely on a molecule called adenosine triphosphate, or ATP, for energy. It’s a universal fuel source that powers everything from muscle contractions to brain function to simply existing. As ATP is utilized, it produces a compound called adenosine. Adenosine is not a waste product. In fact, it is highly valuable. “In muscle, adenosine helps to reduce inflammation and limit damage during periods of metabolic stress,” says Dr. Holmes. Meanwhile, in the brain, adenosine accumulates throughout the day, gradually making you feel sleepier. “In sleep science, this is called ‘sleep pressure,’” says Dr. Holmes.So it seems perfectly plausible that the key to falling asleep faster would simply be to exercise. More exertion equals more adenosine and therefore greater sleep pressure. A 2007 study published in the journal Neuroscience actually found that when rats engaged in intense exercise, the levels of adenosine in their brains increased significantly.But that’s not how it works in humans. "Adenosine can do an awful lot of different things in the brain and in the body, but we have to separate these,” says Dr. Wyatt. This is because adenosine doesn’t cross the blood-brain barrier—the wrapping around your brain that selectively allows certain chemicals in and not others. “If you build up adenosine in your body as a byproduct of exercising, that will not influence what happens in your brain,” Dr. Wyatt says. “That adenosine doesn't make it into the brain.”Make no mistake, adenosine is still crucial for sleep in humans. "Adenosine on its own is one of the major chemicals that helps us fall asleep at night and get deep sleep for the first couple of hours,” Dr. Wyatt says. But only adenosine that is created in the brain will ultimately contribute to increasing sleep pressure.The timing of your workout may be more important than the durationIn terms of how hard or how long you need to work out in order to fall asleep faster, experts aren’t entirely sure of this, or if it even matters all that much. "We don't have a lot of great data on the intensity of exercise that's needed,” says Dr. Wyatt. The main reason for this, it seems, is that exercise’s ability to improve sleep is likely not a direct function of intensity—or any single factor, for that matter—but rather a combination of variables, including timing. For example, working out at a high intensity could be helpful in the morning, but detrimental later on in the day.