Why Good Sleep Is Key for Reaching Your Fitness Goals

Sleep can be just as important as workouts for those who are serious about athletic performance and wellness.

three women resting on a tennis court
Getty Images / Westend61

You’ve probably heard that regular exercise and movement throughout the day can lead to better sleep at night.

In fact, if you’re not sleeping well, exercise is one of the first recommendations to incorporate into your daily routine.

But the reverse is also true. Whether you’re just starting to work out; you’re building stamina and strength to achieve goals; you are taking on a training plan for a race; or you’re a competitive athlete, your sleep could be just as important as the time you spend working out when it comes to performing at your best.

How sleep impacts fitness

Sleep has a tremendous impact on how we function. If you’ve ever pulled an all-nighter studying for a test or battled jet lag after a long journey, you’re familiar with that hazy feeling that can impair your thinking and mood. Sleep impacts not only our mental cognition but our immune system, nervous system, and any other functionality, physically and psychologically.

For sleep neurologist and Sleep.com Sleep Advisor Dr. Chris Winter, exercise and sleep are inextricably connected. As a sleep coach for elite athletes and professional sports teams, Winter travels the country helping align sleep with athletic goals.

One of the reasons is that moderate to intense exercise creates greater accumulation of the chemical adenosine, which is what makes us feel sleepy, he explains. “When we work out extra-hard, we create more adenosine, thus making us want to seek sleep even more. When we don't get enough sleep, we do not get rid of all of the adenosine,” he says. “It's kind of like saying, ‘What happens if we make a big hole in the hull of our ship, but don't work that hard to bail it out?’”

In short, working out naturally makes us tired and if we don’t heed that feeling by getting restorative sleep, some of that sleepiness can linger. Yesterday’s workout paired with a bad night’s sleep could snowball into impaired performance today.

How your body recovers while you sleep

We might think muscle is built entirely at the gym or on the track, but that’s not the whole story. While working out, we’re creating microscopic tears in muscle, Winter explains. When those tears are repaired, they are rebuilt to be stronger and larger, which helps your body become stronger and faster. “A vigorous workout actually damages the muscle fibers at a microscopic level,” he says. “After the workout is when the anabolic process begins to repair and rebuild the muscle to a stronger degree. Think of a callus that is forming as a reaction to an external process, getting bigger and thicker to create protection from this new process.”

Sleep is the time when the body repairs and recovers, through a complex process of hormone release by the endocrine system. So while the gym is a critical part of getting stronger, sleep is critical to utilizing any gains made while you’re there.

What happens if I work out while sleep deprived?

Several clinical studies have examined what happens to physical performance when we’re sleep-deprived. One study that Winter cited focused on male weightlifters, having them sleep normally for four nights followed by four daytime weightlifting exercises. After that, they resumed normal life for 10 days and then spent three consecutive nights sleeping for only three hours. When three of the four weightlifting tasks were performed again, the team noticed a significant performance decrease. According to Winter, it shows that even a few nights of bad sleep can negatively impact performance.

The opposite is true of performance when athletes are thoroughly rested, leading to benefits in strength and speed. A Stanford University study examined the impact of sleep on collegiate swimmers. The participants increased their sleep to 10 hours per night for six or seven weeks. At the end, they noted athletes swam a 15-meter meter sprint 0.51 seconds faster, reacted 0.15 seconds quicker off the blocks, improved turn time by 0.10 seconds, and increased kick strokes by five kicks.

Another Stanford University study examined the benefits of sleep extension for members of the men’s varsity basketball team. After a two- to four-week baseline, players slept for at least 10 hours a night over five to seven weeks, with their athletic performance measured along the way. The study found that during the period of sleep extension, players were not only faster, but more accurate in their shooting, with free throw percentages increasing by 9% and three-point field goals by 9.2%. The study concluded that optimal sleep is “likely beneficial in reaching peak athletic performance.”

But sleep is beneficial even for those who exercise more casually. Winter believes that morning exercise is the best thing that you can do for your body at night, but if you’re giving up necessary sleep to get that exercise, you’re causing more harm than good. “I personally believe sleep’s more important,” Winter says. “I would get that sleep and instead fit exercise into another part of the day.” He recommends taking a walk during lunch, or while waiting for kids at sports practice. “I have an easier time building exercise time into a schedule than taking it away from sleep.”

How sleep benefits cognition and “muscle memory”

Sleep directly impacts our cognition and learning ability. Zack DiCristino, physical therapist and medical manager for the USA Climbing National Team, sees this with all of the athletes he works with, from the youth roster all the way to the team’s Olympic athletes.

“The central nervous system is one of the first things impacted by sleep,” he said. “Not only does this impact your memory, focus, and motivation the next day, but sleep also impacts our working memories.” DiCristino explains that those working memories are a critical part of learning a new task, for example. In his work, this means competitive rock climbers are learning new coordination movements or how to maneuver better on the wall. Without restorative sleep, he says retaining these memories becomes more difficult.

When it comes to memory and cognition, one sleep study went so far as to rephrase the popular saying, “Practice makes perfect,” to “Practice, with sleep, makes perfect.”

This sleep can also reduce the risk of injury. A 2021 study found that athletes who slept for 7 hours or less each night for two consecutive weeks carried a 1.7 times higher risk of sustaining a musculoskeletal injury. DiCristino agrees that injury risk is one of the largest concerns when it comes to working out when sleep-deprived. In his case, training with rock climbers involves precise coordination and quick thinking on the wall to solve problems. Quality rest can cut down on that problem-solving time, while poor sleep can lengthen reaction times.

How much sleep does an athlete need?

So what’s the magic number of hours of sleep to maintain peak physical performance? That answer depends on each individual's needs. While some of us feel great and fully functional with eight hours of sleep, those who are more physically active sometimes need more. DiCristino recommends adult athletes get between eight and 10 hours of sleep, but he also mentions that youth athletes should be getting more like nine to 11 hours. He also notes that the quality of sleep could matter more than the number of hours of sleep in determining how your body will perform or recover.

Winter also agrees that it’s hard to nail down an exact number for all athletes. “Start by going to bed 15 to 30 minutes earlier,” he recommends. “Did you utilize that extra time? Did you feel better? That might be an indication that you were a bit under-slept.”

How to incorporate quality sleep into your workout routine

Whether you’ve just joined a gym, you’re lining up for your first 5k race or you’ve booked your fifth Ironman triathlon, sleep should be considered a tool that’s a critical aspect of training. Here are some tips to get optimal, restorative sleep while training:

  • Practice good sleep hygiene by finding a pre-bedtime routine that works well for you and sticking to it as closely as possible, even on weekends.
  • Maintain a sleep diary to figure out how much sleep you need each night to feel and perform your best. Note what you’ve done each day or night and how you feel the next morning to pinpoint factors that inhibit or improve your sleep.
  • Aim to work out earlier in the day, so that your body is not wound up in later hours as you prepare for bed. A wind-down yoga routine or some evening stretching can help with easing you into a bedtime routine.