What is Core Sleep?

Core sleep is a term you may have seen on smartwatches or on health blogs, for example, and along with "deep sleep", "light sleep", "REM sleep" etc., things can get a little confusing.

Knowing the difference between the various types of sleep is important in the quest for achieving a quality, well-rounded rest. Once you're aware of how they can affect your waking life, resolving the issue is a rather simple process.

Core sleep refers to the second stage of your sleep cycle. A sleep cycle is not your regular sleep routine, but instead a biological process your body goes through when you fall asleep to help your body and mind recover from the day and rebuild for a new day tomorrow.

MedicalNewsToday defines four stages of sleep:

1. A short period of light sleep, occurring during the transitional period of being awake and falling asleep. The body begins to relax its muscles and slow its breathing.
2. A transitional period between light and deeper sleep known as core sleep. This is where a human's breathing, heart rate, and brain waves slow even further.
3. Deep sleep phase - the most difficult phase of the sleep cycle to wake up from. The heart rate and breathing rate are at their lowest and most regular during this stage.
4. Finally, an REM (Rapid Eye Movement) stage occurring after approximately 90 minutes asleep. During this time, the eyes will move back and forth while closed, and breathing and heart rate increases. Dreams can be at their most vivid and the muscles as their most relaxed, which can cause sleep paralysis in some.

The second stage, although not the deepest stage and is easier to wake up from in comparison to REM sleep, is the period of the sleep cycle humans spend most of their time in. Up to 50% of your time asleep will be spent in this stage, with the duration becoming longer each time the cycle restarts.

The core sleep stage helps the body to repair from wear and tear during the day. Your muscles especially become worn with frequent and laborious use, and this stage of sleep is a dedicated time to undo the damage and refresh. The same goes for the mind - a tired brain cannot manage mood, alertness, or productivity well, which is why quality rest is a necessity.

• muscle aches
• brain fog
• poor productivity
• increased sensitivity to pain
• sleepiness and fatigue during daytime
• mood swings
• memory problems

Core sleep accounts for about half of your time asleep. Say, for example, if you got the recommended 7-9 hours of sleep per night - about 3.5-4.5 hours of sleep should be in the core sleep stage.

Sleep devices such as smartwatches and wearable sleep trackers can tell you how much core sleep you're getting, but if the symptoms listed above describe your waking life, you're probably not spending enough time in the core sleep stage.

Poor quality or little core sleep can be caused by, but are not limited to, the following factors:

• not getting enough hours of sleep regularly 
• stress, anxiety, or depression
• sleep apnea
• too hot or cold a climate in the bedroom
• insomnia
• overuse of caffeine
• noisy environments