Deep sleep is one of the 4 stages of sleep (along with light, REM and wake) that your body spends time in each night. Known as the “physically restorative” stage of sleep, it is of great importance for athletes. Below we discuss exactly what deep sleep is, what happens during it, how it benefits you, how much you need and the consequences of not getting enough, as well as what you can do to get more of it.
Shortly after falling asleep, your body transitions from light sleep to deep sleep. This is the stage of sleep when your brain waves are the slowest (and their activity is synchronized when monitored with an EEG). For this reason, deep sleep is also referred to as slow wave sleep (SWS). During this time your muscles relax, and your heart rate and respiratory rate decrease significantly. It can also be difficult to wake up, even when there are loud noises. When you are woken up during this stage, you tend to feel groggy and disoriented.
Your first period of deep sleep each night generally lasts between 45 and 90 minutes. As the night progresses, periods of deep sleep become shorter in the cycles that follow (the average adult typically goes through 3-5 full sleep cycles per night).
Deep sleep and REM (rapid eye movement) sleep are not the same thing. REM sleep follows deep sleep in standard sleep cycles and is the “mentally restorative” stage of sleep–when short-term memories from that day are converted to long-term memories. Unlike deep sleep the brain is very active during the REM stage, when most dreams occur.
As mentioned previously, deep sleep is the time during which your body restores itself physically. In fact, 95% of human growth hormone is produced during deep sleep. What does this mean? You don’t actually get stronger in the gym or while you’re exercising. Working out breaks your muscles down, then deep sleep helps build them back up. In order to see the greatest potential gains from training, getting a sufficient amount of deep sleep afterwards is essential.
The following things also happen during deep sleep:
Below is a healthy breakdown to aim for in terms of percentage of time spent in each stage of sleep:
For most adults, deep sleep normally consists of 15-25% of their total time asleep, usually between an hour or two each night. However, deep sleep also decreases with age. Seniors get less of it than adults, and adults get less than children (primarily because growth and development are key aspects of it).
Learn More: How Much Time Should You Spend in Each Stage of Sleep?
When you’re sleep deprived, deep sleep becomes your body’s priority. If you fail to get the proper amount of deep sleep one night, it will do everything it can to make up for it the next night. For example, even if you have back-to-back nights with below average hours of sleep, on the second night you’ll get a disproportionately high amount of deep sleep to make up for what was lost the night before.
A consistent, long-term loss of deep sleep is likely an indicator of chronic sleep deprivation (or other sleep disorder), which has been linked to greater risk of obesity, Type 2 Diabetes, heart disease, cancer, dementia and depression.
In general, anything you can do to promote better sleep behavior will also help you get more deep sleep–starting by simply spending more time in bed. Check out these 45 tips to get a better night’s sleep.
Additionally, two other things stand out to increase deep sleep. One is something we call sleep consistency, going to bed and waking up at similar times each day. Your body runs more efficiently when it’s on a predictable schedule, and this is particularly true with sleep. An analysis of sleep data from 25,000 WHOOP members showed a distinct rise in amount of nightly deep sleep (SWS) as the percentage of sleep consistency in a 4-day period increased:
The other is to avoid drinking alcohol before bed. When your body is busy processing alcohol it has trouble getting past light sleep and into deep sleep. This is especially problematic because a large portion of your deep sleep usually occurs in the first sleep cycle, which is the one most disrupted by alcohol consumed prior to falling asleep.
Learn More: How to Get More Deep Sleep
WHOOP tracks your sleep in detail each night, telling you exactly how much time you spend in each stage of sleep. There’s also a Sleep Coach in the app which uses your natural circadian rhythm to make recommendations for bed and wake times each day in order to maximize the quality of your sleep. WHOOP will let you know how much deep sleep you’re getting and help you better understand what you can do to get more of it.