Oura's Rem Sleep Measurement Explained

The Oura Ring is a sleep-tracking device that has gained popularity among fitness enthusiasts and celebrities since its debut in 2015. The ring uses infrared and red and green LED light beams to measure sleep through your skin. It also uses an accelerometer to log your activity and movement. The Oura Ring measures four separate stages of sleep: awake, REM, light, and deep sleep. While the ring does not directly measure brain waves like medical devices, it uses a combination of movement, skin temperature, resting heart rate, heart rate variability, and respiratory rate to determine which sleep stage the wearer is in. The Oura Ring has been validated against polysomnography (PSG) — the gold standard sleep laboratory test. Independent studies have shown that the Oura Ring has a 70-80% accuracy when compared to PSG.

The Oura Ring uses infrared PPG, which penetrates deeper than the greenlight PPG in other wearables

The Oura Ring is a health- and sleep-tracking device that has been a favourite of fitness enthusiasts and celebrities since its debut in 2015. The ring shines light beams (infrared and red and green LED) through the skin and uses sensors to measure respiratory rate, heart rate, heart rate variability (HRV), blood oxygen levels, and body temperature. An accelerometer logs activity and movement. The Oura Ring uses infrared PPG, which stands for "photoplethysmography", and refers to the infrared LED that measures heart rate, respiration, and heart rate variability at night. This is sampled at 50Hz, meaning it completes 50 cycles per second. The infrared PPG used by the Oura Ring penetrates deeper than the greenlight PPG in other wearables.

The unobtrusive ring design allows for comfortable sleep tracking without bright screens or notifications disrupting sleep. The ring measures directly from arteries in the finger, rather than the surface capillaries in the wrist. This enables the Oura Ring to capture the signal as it leaves the heart, rather than on a delay on the return. The ring also leverages LEDs on either side of the finger to prioritise the clearest signal.

The Oura Ring is intentionally designed to maximise sleep data quality. The ring's accelerometer sensor sits on the finger, enabling highly sensitive activity detection for even subtle nighttime movements. The Oura Ring is one of the only wearables that directly measures skin temperature, allowing it to detect how the body temperature naturally drops when falling asleep and rises again just before waking up.

The ring measures directly from the arteries in your finger, capturing the signal as it leaves the heart

The Oura Ring is a sleep-tracking device that measures and processes information from several bio-signals. The ring measures directly from the arteries in your finger, capturing the signal as it leaves the heart. This is in contrast to other wrist wearables that measure from the surface capillaries, which causes a delay in capturing the signal.

The Oura Ring uses photoplethysmography (PPG) to measure heart rate, respiration and heart rate variability at night. The PPG is sampled at 50Hz, meaning it completes 50 cycles per second. The ring also has an accelerometer sensor that sits on your finger, enabling highly sensitive activity detection for even subtle nighttime movements.

The Oura Ring uses data from multiple biosignals, including movement, skin temperature, resting heart rate, heart rate variability and respiratory rate, to determine which sleep stage your body is in. When you fall asleep, your body temperature drops, your heart rate decreases, your respiratory rate slows, and your muscles relax. The ring measures these changes to determine when you have fallen asleep.

The Oura Ring then takes all of the data from your night's sleep and divides it into five-minute intervals. It then classifies your data into sleep stages – awake, light, deep and REM – by looking for which sleep stage patterns are most dominant in your data. The ring uses your movement and changes in your heart rate, respiration and temperature to identify the signatures of each sleep stage.

The Oura Ring has been validated against polysomnography (PSG), the gold standard sleep laboratory test. A 2021 validation study of the third-generation Oura Ring indicated that the ring agreed with polysomnography 79% of the time.

Oura is one of the only wearables that directly measures skin temperature

Oura is a sleep-tracking ring that provides tons of data about your sleep and health. It measures and processes information from several bio-signals, including skin temperature.

The Oura ring is one of the few wearables that continuously measures body temperature directly from the skin. It picks up on subtle variations in skin temperature, providing a comfortable and easy way to measure your temperature without disrupting your routine. The temperature sensor can detect changes as small as 0.1° Celsius.

The ring measures your skin temperature at night, as during the day, your average body temperature is impacted by external factors such as eating, drinking, and exercising. By measuring your skin temperature while you sleep, Oura can provide more accurate readings. The ring calculates your normal temperature during the first couple of weeks of wear and adjusts your baseline as needed.

Oura displays changes in your skin temperature as fluctuations from your personal baseline. The closer the reading is to 0.0, the closer your current skin temperature is to your long-term average. You can access your average body temperature trends by selecting "Readiness" from the Oura App's home screen or Vitals tab and then selecting "Body Temperature" above your Readiness Score.

Oura's temperature measurements can be used to identify strain and recovery during physical activity, emerging illness, and phases of the menstrual cycle. For example, you may notice lower temperature trends during your follicular phase and higher trends during your luteal phase.

Oura has a highly sensitive accelerometer to measure your movement

The Oura Ring is a sleep-tracking device that can be worn on the finger. It uses a combination of your body temperature and activity patterns to determine whether you are asleep or awake. The ring has a highly sensitive accelerometer to measure your movement. By being located on your finger, the ring can capture your subtlest movements and detect the differences between twitching in a dream, turning over in bed, and getting up for a nighttime trip to the bathroom.

The accelerometer is one of the sensors that the ring uses to track your sleep. The accelerometer measures your activity and movement. The ring also has infrared and red and green LED lights that shine through your skin, and sensors that measure your respiratory rate, heart rate, heart rate variability, blood oxygen levels, and body temperature.

The Oura Ring uses data from many of your biosignals to determine which sleep stage your body is in. These biosignals include movement, skin temperature, resting heart rate, heart rate variability, and respiratory rate. The ring measures these biosignals throughout the night and then divides your sleep into 5-minute intervals. It then classifies your data into sleep stages—awake, light, deep, and REM—by looking for which sleep stage patterns are most dominant in your data.

The Oura Ring is intentionally designed to maximize sleep data quality. The ring design is unobtrusive, allowing you to measure your sleep comfortably without bright screens or notifications disrupting your sleep. The ring also measures directly from the arteries in your finger, rather than the surface capillaries in your wrist. This enables the ring to capture the signal as it leaves the heart, rather than on a delay on the return.

Oura's sleep algorithm was tested and trained using machine learning

The Oura Ring was designed by experts to empower its members to understand their sleep and health, and to enable researchers to use it as a tool for advancing the understanding of sleep. Unlike other wearables that were originally designed as activity trackers, Oura was engineered to prioritize accurate sleep insights. The Oura Ring delivers research-quality data and has been validated against the gold standard sleep laboratory test, polysomnography (PSG).

In the Oura Ring Gen3, PPG is sampled at 50Hz, meaning it completes 50 cycles per second. PPG stands for "photoplethysmography" and refers to the infrared LED that measures heart rate, respiration, and heart rate variability at night. The unobtrusive ring design allows users to measure their sleep comfortably, without bright screens or notifications disrupting their sleep.

The Oura Ring measures four separate stages of sleep: awake, REM, light, and deep. Every individual's sleep requirements are different, though the recommended amount is 7-9 hours for most adults. This is enough time for the body to go through four to five 90-minute sleep cycles. In general, people spend most of the night in light sleep.

Oura uses data from many biosignals, including movement, skin temperature, resting heart rate, heart rate variability, and respiratory rate, to determine which sleep stage the body is in. The indicators that Oura looks for at each stage include:

• Respiratory rate slows
• Heart rate decreases
• Body temperature drops
• Heart rate and respiration stabilize
• Skin temperature is at its highest
• Respiratory rate increases
• Heart rate increases

Oura's sleep staging algorithm achieved 79% agreement with PSG sleep lab tests.

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