How Bad Is It Really to Work Out Right Before Bed?

Raise your hand if this sounds familiar: You put "exercise" at the top of your to-do list for the day, but things keep popping up — work, phone calls, errands, you name it — and you suddenly find your only workout window is after dinner and before you hit the sheets. But then you wonder: Is it OK to workout before bed?

After all, you've heard it can mess with your sleep. And while the benefits of exercise are seemingly boundless, good sleep is crucial, too.

To solve your dilemma, we tapped experts and dug into the research to find out just how detrimental it is to schedule a workout before a snooze session.

The idea that exercising before bed is bad has to do with the chemicals your body releases during a workout, says Matthew Mintz, MD, a board-certified internist based in Bethesda, Maryland. When you exercise, your brain tells your adrenal glands to make adrenaline, also known as epinephrine.

"Epinephrine kicks the heart into high gear by increasing the heart rate," he explains. This in turn improves blood flow, and therefore oxygen to the muscles, which help overall performance.

However, epinephrine, like caffeine, is also a stimulant, which increases alertness. "This is good for exercise, but not necessarily good for sleep," Dr. Mintz says.

‌Read more:‌ What Really Happens to Your Body When You Have Caffeine

For many years it was just assumed that exercising before bed negatively affected sleep. However, there were little to no studies to back up the concept until recently. These new studies have found that exercising before bed is not only harmless, but may even improve sleep.

A February 2019 review of over 23 different studies published in ‌Sports Medicine‌ discovered that while people who exercised within four hours of going to sleep found no difference in the time it took them to fall asleep, their sleep quality improved. Study participants who exercised also enjoyed more hours of deep sleep than their sedentary counterparts.

However, there are a few factors that play a role in exercise's effect on your sleep.

‌1. Individual Biochemistry‌

Dr. Mintz maintains that there are lots of gray areas when it comes to whether exercising before bed is beneficial, and in many cases, it varies by the person. "Everyone reacts differently," he explains. "For some, the increased epinephrine may be stimulating and make it difficult to fall asleep. For others, being exhausted after a good workout may actually promote sleep. The bottom line is that you really need to listen to your body to determine what's right for you."

‌Read more:‌ 6 Reasons You're Still Tired After a Full Night's Sleep

Lev Kalika, DC, owner of New York Dynamic Neuromuscular Rehabilitation & Physical Therapy in New York City, adds that a person's emotional involvement in the workout can also come into play. "The more excited you are, the harder it is going to be to fall asleep," he explains.

‌2. Workout Intensity‌

As far as whether specific workouts — such as walking vs. HIIT — differ in terms of before-bed benefits or side effects, Dr. Mintz claims there isn't enough research to make that call. However, there is scientific evidence that the intensity of your workout influences sleep.

One small study, published September 2014 in the journal ‌Sleep Medicine‌, surveyed 52 healthy adults who exercised before bedtime and then had electroencephalographic recordings (EEG's) performed to measure sleep. It found that the harder these individuals thought they performed during their pre-bedtime workout, the better they actually slept.

However, a separate review published in the February 2019 journal ‌Sports Medicine‌ found that those who worked out rigorously before bed had more trouble falling asleep because it took more time for their heart rate to normalize and reach resting rate before bedtime.

‌3. Timing‌

This is where timing can matter. According to the study published in ‌Sleep Medicine‌, you should complete your workout at least an hour before bedtime. The researchers found that exercising within the hour can definitely have a negative effect on your sleep.

However, some experts, like Kalika, believe it is best to give yourself about two hours to let your body wind down for bed after a workout.

‌Read more:‌ Morning vs. Evening Workouts: What's Best for Your Goals?

Is exercising before bed something to lose sleep over? Well, yes and no.

If you want to make sure your workouts aren't going to have a negative effect on getting your zzzs, you need to take factors such as timing, intensity of your workout and your body's biochemistry into account. "If you feel that exercising before bedtime makes it more difficult to relax, then don't do it," Dr. Mintz suggests.

If you decide that exercising before bed is right for you, Kalika suggests choosing less-intense and more slow-paced workouts that do not involve emotional energy.

As for timing, just to be safe, Dr. Mintz suggests leaving at least an hour before the end of your workout and shutting down for the night. But listen to your body! If you find that you are having trouble falling or staying asleep, put some more time between your workout and lights out.