How Sleep Affects Fitness

When it comes to working out, you know that what you do in the gym is important. But what you do outside the gym — what you eat, what you drink, and especially how you sleep, is just as crucial. In fact, you must sleep in order for exercise to actually work.

“We exercise for a purpose: for cardiovascular health, to increase lean muscle mass, to improve endurance, and more. All of these ‘goals’ require sleep,” says W. Christopher Winter, MD, the president of Charlottesville Neurology and Sleep Medicine and the author of The Sleep Solution: Why Your Sleep Is Broken and How to Fix It.

Without sleep, exercise does not deliver those benefits, Dr. Winter explains. “If you don’t sleep, you undermine your body.”

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Sleep gives your body time to recover, conserve energy, and repair and build up the muscles worked during exercise. When we get enough good quality sleep, the body produces growth hormone. During childhood and adolescence, growth hormone makes us grow — as the name implies, Winter says. “And when we are older, it helps us build lean muscle and helps our body repair when we have torn ourselves up during a hard workout,” he adds. “Growth hormone is essential for athletic recovery.”

The problem is that Americans have a major issue when it comes to sleep: More than 30 percent of us are sleep-deprived, which means we’re not getting the recommended seven to eight hours a night required for adults. (1,2) And that means more than 100 million people in the U.S. are sabotaging their own fitness goals, too.

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Can exercise help you sleep? Absolutely. And if you’ve never experienced that immediate sleep-inducing exhaustion one might experience after a day of hiking or a grueling boot camp class, there’s a ton of scientific research to back up this claim, too.

In one study, individuals with a self-reported sleep time of less than 6.5 hours completed moderate-intensity workouts (think walking, riding a stationary bicycle, or running or walking on a treadmill) four times a week for six weeks. (3) At the end of the experiment, they reported getting an extra 75 minutes of sleep per night — more than any drug has helped deliver, according to the study authors.

Exercise actually has a chemical effect on the brain. “Physical activity creates more adenosine in the brain, and adenosine makes us feel sleepy,” says Winter. (Fun fact: Adenosine is the chemical that caffeine blocks to make you feel more alert.) “The harder we work out, the more driven we are by this chemical to sleep.”

Working out also helps you maintain your circadian rhythm (that is, your body’s internal clock), Winter says. “Exercise helps your body understand the schedule it’s on; and morning exercise primes your body to sleep better at night.”

But what about late-day exercise? While it is possible that exercising at night will keep you awake longer, science says it’s a matter of choosing the right type of workout and finding the right workout schedule for you.

People who reported greater exertion before bed were actually more efficient sleepers, according to research; they also fell asleep faster, slept deeper, and woke up less during the night. (4) Another study found that moderate-intensity workouts before bed helped soothe presleep anxiety. (5)

That said, you’re probably better off sticking to low-intensity workouts like yoga, pilates, or barre, if you plan to sweat close to bedtime. Research found that high-intensity exercise has been shown to delay sleep onset, probably because of an increased heart rate post-gym time. (6)

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Winter recommends finding out what works for you. Everyone is different when it comes to how stimulating any one particular workout might be. If you have trouble falling asleep, getting your heart rate up too close to bedtime may be contributing to that, but for others, breaking a sweat at the end of the day may not affect sleep.

Again, the short answer is yes. The better rested you are, the better your mind and body function — and that includes at the gym. Adequate sleep has been shown to help motivate people to stick to their exercise plans and work out the next day, according to a study. (7) The more sleep time individuals in the study got, the more likely they were to complete their exercise regimen.

“Getting enough sleep can not only give you more drive and strength to maximize your workout, but its effects on concentration, mood, and focus can make you more efficient and better prepared for that workout,” explains Winter.

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On the flip side, not getting enough sleep can actually make exercise feel harder. (8) Sleep deprivation won’t affect your cardiovascular and respiratory responses to exercise, aerobic and anaerobic performance capability, muscle strength, or electromechanical responses. That means biomechanically there’s no reason sleep will lessen your physical capabilities. But you will fatigue faster on less sleep, making it feel tougher to work out to your maximum capacity.

In fact, even after just one night of not sleeping, endurance performance on a treadmill decreases — likely because it feels so much tougher. (9)

That’s not to say that suddenly getting the requisite seven to eight hours of sleep a night will turn you into a speed demon or a sports superstar. Extra sleep won’t necessarily make you faster, stronger, or improve your times or performance. Rather, sleep loss has been linked to physiological responses — like autonomic nervous system imbalances, which are similar to overtraining symptoms like sore muscles and a higher risk of injuries — that can inhibit your performance. (10)

Getting enough sleep and getting regular exercise are both important, so how do you decide which one takes priority? You really shouldn’t put yourself in that position, because you absolutely need both.

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But if it’s not possible to find that perfect balance all the time, “I would say sleep is always the priority, unless your sleep is almost always sound in quality and quantity,” says Winter.

So if you got seven to eight hours of sleep the night before, get up and hit the gym! But if you’ve been clocking less than six hours most nights that week, you probably want to savor that extra hour of sleep. If you skip it, chances are you’ll log a subpar workout, anyway.

And if you were up all night the night before, definitely choose sleep, Winter says. After an all-nighter (or just a few hours of shut-eye), your body needs the rest more than ever.

The bottom line: If you’re not getting the recommended seven to eight hours of sleep per night, you need to rethink your schedule so you can make sure you do — and then you have to figure out how to fit in your regular workouts without sacrificing that sleep. You can’t have one without the other; both are absolutely essential to you being able to operate at 100 percent — not just in the gym, but in your everyday life, too.