This Is How Your Body Recovers At Night & Why It Matters For Optimal Performance

It’s no secret that sleep is a foundational piece of mental and physical health, but if asked, most people wouldn’t be able to answer why that is.

I mean, think about it: Do you feel like your strongest, fastest, most agile self if you’re exhausted and running on empty? Me neither. So, it’s not surprising that even one night of sleep deprivation1 can decrease muscular endurance and strength, and plenty of research has shown other negative impacts on athletic performance, from increased perceived effort to reduced speed and accuracy.

“Sleep is an essential recovery and growth process. It actively repairs damage, promotes healing and immune defense, regulates emotions, consolidates memories, forms neural connections, etc. When we chronically don't get enough opportunity to meet our sleep needs, we suffer in our health and performance in every way,” shares sleep expert Jade Wu, M.D.

Most of us are at least vaguely familiar with rapid eye movement (REM) sleep, which benefits brain and mental function. Well, non-rapid eye movement (NREM) sleep is the sweet spot for physical recovery, with Stage 3 of NREM considered the deepest sleep of all. With the brain less active during this time, blood supply increases to our muscles and tissues, bringing with it more nutrients to optimize repair and growth. 

But that extra boost in nutrient-dense blood supply isn’t the only magic at work. Shelby Harris, PsyD, DBSM, and author of The Women’s Guide to Overcoming Insomnia, notes that a critical hormonal is also at play. 

“During the deeper stages of sleep, human growth hormone (HGH) is released2, which aids in repairing muscle, strengthening bones, and converting fat to fuel,” she says. “Less sleep leads to reduced HGH levels, impacting the speed from which you recover from workouts.”

Muscle protein synthesis (MPS) is three little words that have become a hot topic.

MPS is how the body uses amino acids to build and maintain muscle. It’s happening all the time, as the body is constantly breaking down muscle and building it back up using the amino acids we consume through protein. 

When we work out, we inflict minor microscopic damage to muscle tissue—I know it sounds negative, but it’s just a normal part of the process. The body is intelligently designed to repair these tiny tears, again through the power of amino acids. Healing this damage, building new muscle, creating new microtears, and repeating the cycle eventually leads to increases in muscle mass.

Among its other superpowers, HGH supports muscle protein synthesis4, which is another reason that the precious HGH spike we receive at night is so supportive of physical recovery. But that’s not the only hormone helping us promote muscle health.

Testosterone typically rises as we sleep, promoting muscle growth and increasing glycogen stores (more on that below). 

Though often associated with men’s health, testosterone is essential for women, too, as it helps regulate muscle mass, strength, and bone density. Women naturally produce testosterone through the ovaries, adrenal glands, liver, kidney, muscle, fat, and skin. Sleep deprivation is linked to reduced testosterone production in both men and women, putting a definite damper on the body’s ability to heal and wake up stronger.

Yet another hormone for optimal muscle growth, maintenance, and healing, insulin-like growth factor-1 (IGF-1) also increases muscle protein synthesis5. It’s especially skilled in activating muscle satellite cells which can replenish muscle fibers. Improving sleep quality is associated with improved IGF-1 levels.

Inflammation is a bit of a misunderstood sibling in the family of physiological processes. Yes, chronic inflammation is harmful and can lead to systemic issues. However, a certain amount of inflammation is a natural part of the recovery process7. 

Those microtears I mentioned earlier? That’s inflammation, and the body’s ability to swiftly respond to it is an integral component of improving strength and endurance while preventing injury. 

As Nishi Bhopal, M.D. says, “sleep is important for immune function, as it enhances the production of antibodies and cytokines that support the body’s response to infections and inflammation.” 

Research shows that sleep does, in fact, boost anti-inflammatory cytokine production8—these are our chemical messengers that regulate immunity, impact blood cell growth, and aid in wound repair. 

Our cardiovascular system also plays a part. When we sleep, our blood pressure drops and blood vessels relax. If we’re deprived of sleep, this process doesn’t occur, and elevated blood pressure can create inflammation through endothelial cells lining blood vessels. 

Cortisol is one of our main stress hormones, and when we sleep, especially in the deep stages of NREM, cortisol levels drop. That’s to our recovery advantage, as consistently high levels of cortisol reduce the immune response9 needed for tissue healing and also make it harder for us to stick with a healthy sleep schedule10. 

There’s a tricky cycle that can happen between sleep and cortisol if things go in the wrong direction. “Sleep deprivation also leads to increased levels of cortisol. More cortisol contributes to slower recovery times,” cautions Harris. 

The darling of nighttime hormones, melatonin11 offers us more than just solid sleep. It happens to also be a powerful antioxidant that inhibits inflammatory enzymes and reduces tissue damage.

Glycogen is a primary source of energy stored in our muscles and liver, which we tap into during intense activity. Ever heard of carbo-loading before a big race or event? Folks do that because the body breaks carbohydrates into glucose, and carbs that aren’t immediately used for energy are stored as glycogen for future needs.

Luckily, carbs aren’t the only way to replenish our glycogen stores during recovery (though they should certainly play a part). Sleep is another part of the equation, as it’s a time the body can reduce energy expenditure and instead focus on replenishment. 

Research shows that two or more hours of moderate exercise12 is enough to significantly reduce glycogen stores and that it can take 24 hours of rest along with adequate carbohydrate consumption to replenish this loss. And sleep deprivation is also linked to reduced muscle glycogen stores.

Wu recommends identifying your sleep chronotype and working with your body’s natural tendencies to get on a healthy schedule. 

It’s not just about our space, Bhopal adds. “Mindset is important here. Prioritize sleep and think of it as part of your training routine. A consistent sleep schedule regulates the circadian rhythm and helps maintain a healthy body clock and sleep architecture.”

Sleep is a must-have part of recovery and an essential aspect of optimizing both physical and mental performance. From muscle protein synthesis to reduced inflammation, it offers the body a change to repair and grow stronger.