How Sleep Affects Fitness: Weight Loss, Muscle Growth, and Overall Health
- Deb Cano
- Oct 7
- 11 min read
How does sleep affect your fitness goals?
Whether your goal is to lose weight, build muscle, or maintain overall health, sleep plays a massive role in your fitness results. In this article, you’ll learn exactly how sleep affects your fitness goals — and how to improve your sleep for better recovery, performance, and results.
Let's first look at how it affects your weight loss goals.
How Sleep Affects Weight Loss
Lack of sleep doesn't directly make you gain weight, nor does it directly keep you from losing weight.
An energy balance determines your weight.
Our bodies use calories as the unit of energy. We eat a certain amount of calories, and we expend a certain amount of calories.
If you eat more calories than you burn, you will gain weight. That means you are in a calorie surplus.
If you eat the same amount of calories as you burn, you will maintain your weight. That means you are in a calorie maintenance.
If you eat fewer calories than you burn, then you will lose weight. That means you are in a calorie deficit.
This is how our bodies lose, gain, or maintain weight.
In the end, if your goal is to lose weight, you'll need to be in a calorie deficit, because that's the only way you will lose weight.
Now, how does sleep affect your weight loss goals?
How Sleep Affects Fitness Through Hunger Hormones (Leptin and Ghrelin)
When it comes to sleep and weight loss, poor sleep can disrupt hunger hormones, making it harder to maintain a calorie deficit.
However, before you start blaming your hormones for not losing weight, let me explain what happens to your body when you are not getting enough sleep.
There are two hormones in your body called Leptin and Ghrelin.
Leptin decreases appetite.
Ghrelin increases appetite.
One controlled study demonstrated that acute sleep deprivation decreased leptin levels and increased ghrelin levels.
While you sleep through the night, leptin levels increase and ghrelin levels decrease.
This is because you are sleeping. There is no need for you to be eating. This is the time for your body to recover. Your body is going through a parasympathetic state.
That is why your leptin levels increase. To signal to your body that you are not hungry.
However, if you are awake, your body is not in a parasympathetic state, and your leptin levels are not being increased.
This means that your ghrelin levels are being increased. You know those late-night cravings you get late at night, yep, that's your ghrelin levels. And those cravings are typically for highly palatable, high-calorie foods. You don't usually crave carrots or apples late at night.
In one experimental protocol, sleep restriction increased ghrelin levels, leading to ~300 kcal more in snack intake.
So, if you are constantly under-sleeping, this means your leptin levels are constantly lowered and your ghrelin levels are constantly increased.
This leads to you being hungrier, which leads to you taking in more calories.
If you consistently take in more calories than your body needs, that means you are in a calorie surplus. And a calorie surplus will lead to weight gain.
Lack of sleep causes you to have less energy, which can prevent you from getting your workouts in, especially when you have other responsibilities, such as work or family, and you're already tired.
When you're tired from lack of sleep, you're not going to feel like cooking a healthy meal. All you're thinking about is what is the fastest way I can feed my family and myself so I can just sit down and relax.
A lack of sleep equates to a lack of energy, which can result in a decrease in energy expenditure. You're skipping workouts and not eating the healthiest foods. These actions make it harder for you to be in a calorie deficit, which doesn't lead to weight loss.
How Sleep Affects Fitness: Training, Nutrition, and Muscle Growth
You probably know that you need to train to build muscle and that your nutrition plays a crucial role, especially in eating enough protein to support muscle growth.
However, sleep also plays a role in building muscle.
Training and Building Muscle
First, when you train hard, you are damaging your muscles and creating other forms of fatigue in your body that your body needs to recover from.
That's the signal that tells your body to build muscle.
It goes something like this:
1) Let's say you did 10 push-ups in your training session.
2) Your brain recognizes you just did something challenging, and it tells your body, "We need to get stronger and build more muscle so when we do this again, it's not so hard."
3) That's the signal your body needed to start building muscle.
Then, repeating that for many, many months and years to see considerable muscle gains.
Nutrition and Protein Intake
After you've challenged your body by training hard, your body needs building blocks to grow and repair the muscle tissue that was damaged during your training session.
That's why nutrition matters.
Building muscle is most easily done while eating in a calorie surplus. If you remember, that means you're taking in more energy (in the form of calories) than your body needs each day. It can also be achieved while eating at maintenance (eating the same amount of calories as you burn), but it's easier if you're in a slight calorie surplus.
And it's not just about the calories, you'll also want to ensure you're eating enough protein. Protein provides the nutrients needed to repair and grow muscle tissue.
So if you:
1) Eat in a slight calorie surplus (200-500 calories of a surplus on average).
2) Eat enough protein per day (.7-1 gram per pound of body weight or lean bodyweight).
3) Eat mostly whole, highly nutritious foods.
Do this consistently and repeat it over and over, again and again, for a very long time. Combine it with strength training, and it will help you build muscle.
How Sleep Affects Fitness and Building Muscle
Now we get to why sleep matters and what role it plays in building muscle.
If your goal is to build muscle or improve performance, sleep is when your body repairs, grows, and strengthens your muscles.
While sleeping, your body produces growth hormones, which are a primary driver of recovery and growth.
Cells and tissues are undergoing reconstruction, and your body essentially restores itself. Sleep is the period of time during which the majority of the muscle tissue gets repaired and rebuilt.
Deep sleep and REM sleep are both vital for muscle recovery, hormone production, and strength gains.
So if you don't get enough sleep, your body struggles to repair, restore, and recover your muscles.
Not to mention, if you are sleep-deprived, you won't have the energy to push yourself during your workouts, which can hinder your ability to continue seeing results.
When your sleep improves, so does your consistency in training, because you have the energy to show up.
As you can see, sleep is beneficial for building muscle.
How Sleep Affects Fitness and Overall Health
Quality sleep improves not only your physical fitness but also your overall health — from a better mood and improved memory to stronger immunity and faster recovery.
Your life is just much more enjoyable with good quality sleep.
Sleep plays a crucial role in memory, learning, and mental health.
Sleep helps us have a strong immune system. It's no coincidence that when we feel ill, whether with the flu, a cold, or are recovering from an injury, we tend to sleep more. That's because sleep plays a crucial role in recovery.
Sleep helps with emotional stability. You'll be less irritable. You'll be able to make better decisions after a good night's sleep. Your relationships will be better, you'll be able to have better conversations.
There would be less road rage and fewer accidents when people get enough sleep because they would be more emotionally stable.
You'll be more focused and productive at work, which can lead to a raise. Whether you are self-employed or not, better sleep can definitely lead to making more money.
The Four Stages of Sleep (and Why They Matter for Recovery)
While we sleep, both our brain and body go through a powerful process of restoration and repair.
There are four main stages of sleep, and cycling through all of them is key to getting the full benefits of recovery.
Stage 1: Light Sleep
The transition phase between being awake and asleep.
Lasts just a few minutes.
Breathing, heart rate, and brain waves slow down.
Helps your body ease into deeper, more restorative sleep.
Stage 2: Deeper Light Sleep
Makes up the majority of your total sleep cycle.
Heart rate and body temperature drop further.
Brain activity slows, supporting memory and learning.
Plays a major role in overall recovery.
Stage 3: Deep Sleep (Slow-Wave Sleep)
The most restorative phase of non-REM sleep.
Breathing and heart rate reach their lowest point.
Your body releases the highest amounts of growth hormone, crucial for:
Muscle repair
Tissue growth
Full recovery from tough workouts
If your goal is to build muscle or improve recovery, this stage is non-negotiable.
Stage 4: REM Sleep
Stands for Rapid Eye Movement.
Brain activity increases again, similar to when you’re awake.
This is when most dreaming happens.
REM sleep is vital for:
Cognitive function
Memory and emotional regulation
Motor learning and coordination
Why All Stages Matter
Your body cycles through these stages 4–6 times per night. Missing out on enough total sleep means cutting short one or more stages, which can impact:
Muscle recovery
Hormone balance
Focus and consistency in training and nutrition
Tip: Keep Your Sleep and Wake Times Consistent
Try to maintain a consistent sleep and wake schedule—ideally within about an hour each day. This helps stabilize your circadian rhythm, allowing your body to move more efficiently through all sleep stages and recover more effectively.
How to Build a Better Sleep Routine for Fitness
Your sleep routine will help you consistently get the 7-9 hours of sleep you need.
Believe it or not, your sleep routine actually starts when you wake up in the morning. Waking up at roughly the same time each morning, consistently, including weekends and yes, even Sundays, will eventually help your body get used to a consistent sleep-wake rhythm.
Note: You shouldn't need "extra" sleep on the weekends if you're getting enough sleep every night.
Starting your day with sunlight on your skin first thing in the morning helps your circadian rhythm, which is heavily influenced by direct sunlight.
When you get sun exposure early in the morning, that's telling your body it's time to be awake, alert, and energized.
Caffeine Cut-off Time
Caffeine has a half-life of 4-6 hours. This means that if you drink a coffee or an energy drink with 100 mg of caffeine in 4-6 hours, you will still have half of that amount, or 50 mg of caffeine, in your body.
Alcohol and Sleep Quality
Alcohol negatively impacts your sleep.
Some use alcohol as a way to wind down from a stressful day, not knowing the negative impacts it has on their sleep.
Alcohol shouldn't be used as a sleep aid. If alcohol is knocking you out, you're not getting good quality sleep.
Consuming more than a couple of glasses can have a negative impact on your sleep, especially if it's too close to bedtime.
Screen Time and Blue Light Exposure
You want to have no screen time 30 minutes to 2 hours before bed. No screen means no phones, no tablets, no TV, no laptops, and so on.
No scrolling on social media. Whatever the news, whether good or bad, it will still be there the next day. It can wait! And quite frankly, most of the news you consume is counterproductive to a good night's sleep. Social media is designed to keep you watching and to initiate a specific reaction, and that is primarily a negative reaction these days, which is the complete opposite of what you want when you're winding down. You want to feel relaxed and calm as you get ready for bed.
Staring at a screen, whether on your phone or another device that emits blue light, has been shown to negatively impact your body's ability to secrete melatonin and wind down for sleep.
Here are a few things you can do before bed that doesn't include screens.
1) Read
2) Journal
3) Stretch
4) Meditate
Creating a Bedtime Routine
For optimal fitness recovery and performance, aim for 7–9 hours of quality sleep per night.
That doesn't mean 7 hours lying in bed. If you're in bed for 7 hours, you're getting about 6 hours of sleep. You're not sleeping the whole time you're lying in bed. It takes you about 20 minutes to fall asleep, then you wake up to pee in the middle of the night. So even if you're in bed for a whole 7 hours, you're not sleeping the entire time.
Let's work backwards from your wake time. Let's say you have to wake up at 6 am, then you should aim to be in bed by 10 pm. That will give you 8 hours in bed and about 7 hours of sleep.
With a bedtime of 10 pm, this means you should start heading to bed by 9:30 pm, not 10 pm.
Sleep in a cool room. Ideally, the temperature should be 68°F or cooler.
Sleep in a dark room. Dark out curtains, no alarm light, and an eyemask are helpful.
FAQ: Sleep And Your Fitness Goals
What if I work night shifts and I get most of my sleep during the day?
This is definitely tough. First, ensure you're doing everything in your control to stick to a sleep routine and set up your environment for good quality sleep, the best you can. This means sleeping in a quiet, cool, dark room, being as consistent as you can with your sleep schedule, and still aiming for 7-9 hours of sleep. Do everything I outlined above, just during the day. Everything still applies.
What if I only sleep 6 hours?
Six hours is obviously better than 5 hours or less. Do your best to make those 6 hours of sleep the best quality sleep you can. However, try to get at least 7 hours of sleep. Begin by reviewing your schedule and sleep routine to identify areas for adjustment, aiming to gain 15-30 minutes of additional sleep. Then, in two weeks, audit your schedule again and see if you can squeeze another 15-30 minutes of sleep until you're getting 7 hours of sleep. You'll notice a difference going from 6 to 7 hours.
Is it true that some people function well on 4 or 5 hours of sleep?
I feel like many people brag about how they can get by on 4 or 5 hours of sleep. The truth is, you might think you do just fine on very little sleep, but going from 5 hours or less of sleep to 6, then to 7 hours, will not only help you achieve your fitness goals faster, but you will also feel better. Try it!
Further Reading & Resources
If you’d like to dive deeper into the science and strategies of sleep, here are two excellent books I recommend:
Sleep Smarter by Shawn Stevenson — A practical guide packed with 21 strategies to improve your sleep and overall health.
Why We Sleep by Matthew Walker, PhD — A deep dive into the science of sleep, how it impacts every aspect of health, and why prioritizing it is non-negotiable.
Sleep And Your Fitness Goals: Conclusion
Just like training and nutrition are integral to your fitness goals and impact whether you lose weight or gain muscle, sleep also plays a crucial role in your fitness progress.
Consistently sleeping 7-9 hours a night will help you recover from your training and feel refreshed and energized to train again the next day.
Going to bed between 10 pm and 11 pm will ensure you naturally align with your circadian rhythm.
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I hope you found this article helpful! Now you know, sleep is essential when it comes to your overall health.
If you’re ready to finally put the pieces together — training, nutrition, sleep, and overall health routine — this is what I do, I'm here to help!
Apply here, and let’s build a program that helps you become stronger, healthier, and feel your best.
Thanks for reading!
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