Oura identifies light sleep, deep sleep, REM sleep and awake time. This article describes what goes on in your body during each stage.
Understanding your readiness starts with understanding how you sleep. Sleep is the most important time for your body and mind recover from your daily challenges. It’s the time your brain flushes out toxins and your cells and tissues grow and repair.
Getting enough restorative sleep helps keep your autonomic nervous system and hormonal and immune system functions balanced. And when you’re balanced, you sleep better. It’s a virtuous cycle that affects every aspect of your health and performance.
Understanding sleep stages
Sleep can be divided into two basic categories: Non-rapid eye movement sleep (NREM) and Rapid eye movement sleep (REM) which alternate in approximately 90-minute cycles throughout the night. Each sleep stage has its own characteristics, which are reflected in your metabolic, immune and autonomic nervous system functions in a number of different ways.
Light sleep makes up about 50% of total sleep time for adults, and typically begins a sleep cycle. Light sleep consists of N1 and N2 sleep, which are the first two stages of NREM sleep. Sleep usually begins with N1, which is a very light sleep stage between sleep and wakefulness. Typically most light sleep is N2 sleep. Deeper than N1, stage N2 sleep also prepares your body for transitions between sleep stages. During this stage your muscles begin to relax, your heart and breathing rates slow down, but you still wake up quite easily.
Deep Sleep or N3 is the third stage of NREM sleep. It's the most restorative and rejuvenating sleep stage, enabling muscle growth and repair. When you're in deep sleep, your blood pressure drops, heart and breathing rates are regular, arm and leg muscles are relaxed and you're very difficult to awaken.
The amount of deep sleep can vary significantly between nights and individuals, and it can make up anywhere between 0-35% of your total sleep time. On average adults spend 15-20% of their total sleep time in deep sleep, the percentage usually decreasing with age.
Regular physical activity, avoiding heavy meals and alcohol before bed and long naps and caffeine in the afternoon can improve your chances of getting more deep sleep.
REM Sleep plays an important role in re-energizing your mind and your body. REM is associated with dreaming, memory consolidation, learning and creativity. Making up anywhere between 5-50% of your total sleep time, the amount of REM can vary significantly between nights and individuals. On average REM counts for 20-25% (1,5h - 2h) of total sleep time for adults, and it also usually decreases with age.
REM is regulated by circadian rhythms, i.e. your body clock. Getting a full night's sleep, sticking to a regular sleep schedule and avoiding caffeine, alcohol or other stimulants in the evening can increase your chances of getting more REM.
Awake time is the time spent awake in bed before and after falling asleep. Measuring the time it takes for you to fall asleep (sleep latency) and the time you spend awake in bed after going to sleep can be used to evaluate your sleep quality. A high amount of awake time can indicate difficulties falling or staying asleep. It's also usually connected to daytime sleepiness.
Read more: Stages of Sleep: The Definitive Guide for the Curious