The Critical Importance of Sleep For Fitness and Health

In the world of fitness, topics like muscle growth, fat loss, strength gain, the latest fat burner pill, and how to optimize your hormones often take the spotlight.

And while most of these topics matter and we should strive to educate ourselves, one vital topic is often left in the shadows.

That topic is on the importance of sleep.

Indeed, adequate sleep is vital, yet most people don’t recognize its importance.

Today, we’ll go over everything you need to know about sleep, what effects it has on the body, and how to improve yours for optimal fitness progress and good health.

The Critical Importance of Sleep For Fitness and Health

The Vital Importance of Sleep

To realize how important sleep is for us, I’d like to bring your attention to a study that was published back in 2010.

The study’s name? “Insufficient sleep undermines dietary efforts to reduce adiposity.”

The title pretty much sums it up, but let’s take a more in-depth look:


Nedeltcheva and colleagues wanted to determine what effects sleep deprivation had on fat loss efforts. The participants were ten overweight but otherwise healthy individuals between the ages of thirty-five and forty-nine. None of the participants had self-reported sleep issues, consumed excessive amounts of alcohol or caffeine, smoked, or had unusual medical histories. In other words, they were pretty healthy and normal, middle-aged folks.

All of the subjects went through a couple of sleeping protocols that were conducted at least twelve weeks apart. Both conditions lasted for two weeks.

In the first condition, subjects stayed in bed for 8.5 hours per night, which resulted in an average of 7 hours and 25 minutes of actual sleeping time. In the second condition, subjects spent 5.5 hours in bed, which, on average, led to 5 hours and 14 minutes of sleep.

In both cases, subjects were also put on a calorie-restricted diet and consumed about 1,450 calories per day, which put them at a reasonably aggressive deficit of about 700 calories per day. In both conditions, the diet composition was the same: 


  • 48 percent of calories came from carbs;
  • 34 percent of calories came from fats;
  • 18 percent of calories came from protein;


My only critique is that their protein intake was quite low, especially given the aggressive caloric deficit. On average, that meant the subjects consumed about 65 grams of protein per day. 

Now, here is where it gets interesting:

In both conditions, subjects lost about 6.6 pounds of weight in two weeks. But, in the sleep-deprived state, subjects lost nearly 80 percent of the weight from lean tissue, and only 20 percent came from fat. Meaning, for every five pounds of weight loss, only one came from fat!

When subjects stayed in bed for 8.5 hours, they still lost 6.6 pounds of weight, but now they lost fat and lean tissue at a one to one ratio. Meaning, about 3.3 pounds came from fat, and 3.3 pounds came from lean tissue.

That’s a huge difference. And, keep in mind that everything except their sleep time was the same - their diet, exercise, and habits. They were the same people, and how long they slept was the only thing that changed. Yet, it resulted in such profound differences in fat loss.

In the sleep-deprived condition, subjects also had higher levels of ghrelin (a hunger hormone) and reported higher hunger and more cravings.

Granted, the study wasn’t perfect and had its flaws. But researchers ensured identical conditions in both cases, and this indeed suggests that sleep is vital for fat loss.

The Critical Importance of Sleep For Fitness and Health

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When it comes to muscle growth, good health, and cognitive function, things aren’t much different - we need to sleep.


For example, sleep deprivation hinders muscle growth for two reasons:


  1. It leads to lower levels of testosterone and IGF-1 (source, source, source) - two hormones that play a huge role in muscle growth.
  2. It impacts gym performance, and thus hinders your ability to accumulate training volume, which is vital for muscle growth.


It’s been well-established that testosterone plays a huge role in muscle growth and protein synthesis. The hormone binds to androgen receptors and increases protein synthesis. Testosterone also has a hand in the mTOR pathway, which plays vital roles in longevity, muscle growth, and more.

IGF-1 has some similar effects and also plays a role in the mTOR pathway, helping optimize protein synthesis. 

What’s more, sleep deprivation appears to raise levels of cortisol - the stress hormone. Spikes in the hormone are healthy and beneficial. But, when cortisol is chronically elevated, it leads to adverse health effects, muscle breakdown, water retention, and an inability to sleep (thus creating a cursed cycle).


And, lastly, sleep deprivation affects our cognitive function (ability to focus, to make decisions, to use our critical thinking skills, and more), subjective mood, motivation, and more.

It’s clear that to stay healthy, feel good, perform optimally, and make the best fitness progress possible, we need to get adequate sleep. The question is, how much would that be?

The Critical Importance of Sleep For Fitness and Health

How Much Sleep Do We Need?


First of all, it’s important to remember that sleep deprivation is a cumulative issue. As you sleep less than you should night after night, your ‘bucket’ of sleep debt fills up. The longer you spend in this sleep-deprived state, the worse the symptoms become.


For example, this study from 2004 examined three sleep lengths and their effects on the subjects. Researchers had 48 healthy and young adults and split them into four groups. One group had to stay up for three days without sleep, one group got to stay in bed for four hours, one stayed in bed for six hours, and the luckiest of all got to stay in bed for eight hours per night. The intervention lasted for two weeks.


Researchers found that the subjects who slept for four hours displayed the greatest mental decline as the days passed. The group that slept for six hours did a bit better, but not by much. The group that stayed in bed for eight hours displayed no cognitive decline throughout the study.


Researchers found that sleep debt is very much a real thing, and 25 percent of the subjects who slept for six hours began falling asleep at random times during the day by the end of week one. By the end of week two, the same subjects displayed a cognitive decline that would be considered equivalent to that one would experience if they stayed up for two days straight.


Frankly, we can’t give a single answer to the question of, “How much sleep do we need?” We are all different, and thus, we all have different needs. But, as far as research goes, it seems that seven to nine hours are the sweet spot for most people. So, make sure to fall somewhere in that range for optimal health, well-being, and fitness.

The Critical Importance of Sleep For Fitness and Health

The Negative Effects of Sleep Deprivation


The greatest irony with sleep is that we tend to sacrifice it, so we have more time to do work and run errands. But, sleep deprivation hinders our performance, and those extra hours we’ve ‘saved up’ are more or less wasted. 

Not only does the lack of sleep lower our productivity, motivation, cognitive function, and ability to concentrate, it also makes us more irritable, more impulsive, and less able to control our urges.

Also, sleep deprivation lowers our overall athletic performance, hinders our recovery, reduces our ability to burn fat, and puts us at a higher risk of muscle loss (especially while dieting).


How to Sleep Better: Three Proven Tactics

Before wrapping this guide up, let’s go over some actionable ways to get better sleep.

The Critical Importance of Sleep For Fitness and Health

1. Exercise Regularly

Research is largely in agreement that regular physical activity leads to improved quality (and quantity) of sleep. 


2. Avoid Alcohol and Caffeine Consumption In The Hours Before Bed

Alcohol, in particular, is often used as a sleep aid. While most use the regular ‘nightcap’ to fall asleep more easily, alcohol can decrease the quality of sleep and delay the onset of the REM cycle.

And, as a stimulant, caffeine should also be avoided within eight hours of going to sleep as it can make it difficult (impossible even) to fall asleep. And, when you eventually fall asleep, you’re much less likely to get enough deep, restorative sleep.


3. Create The Perfect Sleep Environment

Having a pleasant sleep environment is crucial. Here are some ideas:


  • It’s best to cool down your room. Most folks sleep best at temperatures between 65 and 70 degrees Fahrenheit (or 18 to 21 degrees Celsius).
  • Make sure that your room is completely dark, as light can often interfere with your sleep. Blackout curtains are a good idea.
  • A quiet room is vital for restful sleep. So, do your best to insulate your room. If that’s not an option, you can also get yourself earplugs from the local drug store.
  • Invest a bit of money in a decent mattress and pillow. Sure, they aren’t the cheapest home items to buy, but a good one will last you for well over a decade.