If you’ve ever thrown down a hard one at the gym, you’re familiar with the soreness that lingers in the hours, days, and even weeks following the workout. You’ve damaged your muscles. That’s why they’re sore.


Fortunately, your muscles adapt to this damage by growing back stronger. The term for this adaptation is hormesis, and it’s why exercise is so healthy in the first place.


But in order for this adaptation to occur, your body needs certain inputs. Protein is a big one. You can’t build muscle if you don’t have enough amino acids in your blood.


Sleep is another, and it’s the centerpiece of this article. When you sleep, you unleash a hormonal cascade necessary for muscle growth and recovery. Let’s look at three of these hormones.


1) Growth Hormone (Yeah, It Helps Us Grow)


Growth hormone (GH) is a natural molecule in the human body that helps our cells replicate and repair. GH is anabolic, meaning it helps us get bigger.


The issue is: when we hit about 30, GH production starts to decline. Between the ages of 30-40, in fact, GH levels can decrease by a factor of 2 to 3. Not ideal if you’re trying to put on muscle.


Here’s where sleep comes in. Sleepy time is when growth hormone gets secreted, and as we grow older, adequate slow wave sleep helps maintain GH levels.  


But no matter our age, GH production suffers when we don’t sleep enough. And when GH production suffers, muscle recovery suffers too. So to develop strong and healthy muscles, it makes sense to prioritize sleep.


2) Testosterone (Not Just A Sex Hormone)


Closely linked to growth hormone is testosterone, the prototypical male sex hormone. Like GH, testosterone is anabolic. It helps all humans build muscle, not just humans with a Y chromosome.


Also like GH, testosterone production depends upon sleep. Can you guess what happens when we don’t get enough Zs? That’s right, testosterone declines. And it stays declined all day.


Since testosterone (like GH) is crucial for muscle growth and repair, low levels of this steroid hormone will hamper your efforts to put on lean mass. The solution? Get under the dang covers and stay there for at least 8 hours.


3) Cortisol (Sleep Deprivation Is Stressful)


Cortisol – the “stress hormone” – acts differently than testosterone and GH. Cortisol is our body’s response to acute stress. It prepares us to flee from predators, real or imagined.


But cortisol does not help you recover from a heavy session at the gym. That’s because cortisol is catabolic. In other words, it breaks down muscle.  


As you may have guessed, sleep plays a major role in regulating this hormone. In one study, partial sleep deprivation caused a 37% rise in cortisol over baseline levels. And total sleep deprivation? A 45% rise.


We return again to the common theme. Sleep deprivation causes hormonal issues, which in turn leads to impaired protein synthesis and muscle development.


If you don’t get enough sleep, other bad stuff will happen too. Sleep deprivation will make you sad, slow, and sick. Sleep deprivation will bury you.




To recap, growth hormone, testosterone, and cortisol are three hormones that factor heavily into muscle growth and repair. To make these hormones play nice, we need plenty of Z’s.


So next time you pump some iron, do your muscles a favor. Sleep.

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