The Different Stages of Sleep (And What They Mean)


You might know that there are various stages of sleep, but more than likely, you mostly know that some mornings you wake up refreshed, and other times, you feel like you could sleep for a year. What are the different stages of sleep, what roles do they play, and why should you care?

Moreover, what does sleep have to do with your progress in the gym and how well your body is able to recover from the (good) stress you put it through during training?

What Are the Stages of Sleep? 

According to, your sleep cycle includes two main parts: non-REM (rapid eye movement) and REM sleep. Non-REM sleep includes four phases.

Phase 1

Right after dozing off, your brain starts to produce alpha and theta waves. Your eye movement slows down. This phase will last up to seven minutes in duration, and you're still somewhat alert and can be woken up fairly easily.

alarm clock

Phase 2

Your brain waves slow down, but this is still a stage of pretty light sleep. Your brain wave frequency increases, producing "sleep spindles." Sleep spindles get their name because of the way they look on an EEG reading. Tuck defines them as "sudden bursts of oscillatory brain activity generated in the reticular nucleus of the thalamus that occur during stage 2 of light sleep."

Phases 3 and 4

This is where you begin to transition into a deep sleep. The delta waves that your brain is producing slow down but increase in number. You exhibit no eye movement or muscle activity, and you won't respond nearly as much to outside stimuli. 

These two phases are so important because this is the time when your body will start to repair and recharge your muscles and tissues. The exhaustion you feel after a big training day? That DOMS you've got from a particularly grueling workout? This is the prime time for all of those things to begin their healing process. 

You'll also restore energy for the upcoming day, and your immune system gets a nice boost. 

Now, what happens once you hit REM sleep? 

man sleeping on bench

REM Sleep

Around 90 minutes after falling asleep, you hit the REM stage. Most adults have somewhere between five and six REM cycles per night, and each one can last up to an hour. Your brain is more active here, your heart rate and blood pressure go up, you breathe faster, and your eyes dart in different directions. This is also when you'll have dreams. 

It's so vital to hit REM sleep because it plays such an important part in your learning and memory. This is your brain's opportunity to process all of the information it took in the day prior so that it can file it away in your long-term memory.

All of these steps make up your main sleep cycle, which (according to Tuck) lasts about 90 to 120 minutes before repeating. 

How Does Sleep Affect Your Fitness?

It's clear why sleep is necessary for your overall health; but what's the relationship between sleep and fitness specifically?

For starters, if you don't get enough sleep, you might not feel the motivation to exercise in the first place, since the two are positively correlated. True, motivation is largely mind over matter. But with the way sleep affects your hormones, it can indeed impact the way you feel emotionally — and that includes your motivation (or lack thereof).

Plus, because sleep affects your energy levels, a lack of it can have you dragging in the gym. You might experience difficulty training for as long or as hard as you normally would. Some people try to power through this, but that could easily lead to burnout, sickness, and overtraining. If your body is screaming for sleep, let it have it. 

man running on treadmill

And on a related note, sleep is vital — vital! — for your recovery. Recovery won't happen without it. Not only will a lack of sleep slow down the healing process, but it can negatively impact other metrics, as well. 

For instance, did you know that not getting enough sleep can increase your heart rate variability (HRV)? This ultimately means that your body is going to be more stressed. And when your body is stressed, it works harder to function throughout your everyday life. Everything suffers — sleep, recovery, hormones, everything. 

This conversation is a giant web, and everything affects everything, but here's the takeaway: A lack of sleep > diminished recovery > increased HRV > increased stress > a lack of sleep. It's a concerning cycle.

Safety Concerns

It might not be safe to train when you're especially tired, either. A lack of sleep might have the same effect on your body as alcohol, slowing your reflexes. If your plan is to throw some heavier weights around, you might want to rethink that. Your body isn't in a position to react as quickly as it will need to.

Furthermore, as you now know, sleep is an opportunity for your body to heal. If you're training hard and not giving yourself ample time to recover, you could experience burnout or even injury. Sleep is when your muscles relax the most. More blood flows to them, lactic acid breaks down, tissue growth and repair happen, and HGH (human growth hormone) is released, which helps support your immune system and metabolism.

The Impact of Fitness on Sleep

And make no mistake about it: Fitness affects sleep, as well. Mounting evidence — including research published in Advances in Preventative Medicine — confirms that physical exercise is an effective way to improve sleep duration and quality.

Sure enough, people who exercise experience better sleep. The 2013 National Sleep Foundation Sleep In America Poll found that 75% of exercisers reported very good or fairly good sleep quality, compared to about 50% of non-exercisers. Furthermore, they found that people who don't exercise have a higher risk of sleep apnea.

tired man sitting at table

Americans Are Tired

Sleep is serious business, but unfortunately, most of us are walking around tired. Information from Statista says that 45% of us getting seven to eight hours a night still report being tired or fatigued up to three times a week. 27% of us wake up tired four or more times a week.

The demands of work and life have a large piece of us walking around perpetually tired.

So, What Can You Do About It?

The best to improve something is to track and measure it over time. Are you really getting as much sleep as you think you are? 

What's more, even if you are, is it the number of hours that your body needs? 

There's only one way to know for sure, and that's to track you sleep using something like Atlas Wearables. It's not uncommon for people to think they're getting a solid eight hours, only for their Atlas watch to tell them it's closer to five or six — and that makes a huge difference.

We'd like to leave you with some helpful tips for getting more sleep — but not the common ones you've already heard a million times. 

1. Increase Your Exposure to Natural Light During the Day

You probably already know to avoid blue light at night, which is why you want to stay away from your phone. However, getting more natural light during the day could also help, because it aids in keeping your circadian rhythm healthy.

hand in sunlight

2. Turn Down the Thermostat

It's so relaxing to curl up under the blankets so you're nice and warm at night, but you might want to consider turning the thermostat down so it's even cooler. says the best temperature for sleep is somewhere between 60 and 67 degrees Fahrenheit.

This is because your body's temperature naturally decreases in preparation for sleep. If you give it a little nudge, it could improve your sleep further, signaling to your body that it's time to get some rest.

3. Clear Your Room of Clutter

Is your bedroom a little messy? Clean it up! Research has found that your duration and quality of sleep could be negatively affected if your room has a lot of clutter.

Sleep is crucial not to just your health and your fitness, but your survival. If you want to see progress in the gym, there's no doubt about it. You need to sleep to get stronger and recover properly. Take it seriously and feel the difference.