Whoop's Tracking Abilities: Do They Include Rem Sleep?

does whoop track rem sleep

The Whoop Strap Fitness Tracker is a wrist-worn device that provides insights into your health and wellness by tracking your sleep, heart rate, and recovery. Whoop claims to track all four stages of sleep with near-perfect accuracy: slow-wave sleep (SWS), REM, light, and awake. However, some users have questioned the accuracy of Whoop's sleep measurements, particularly when differentiating between light sleep and sedentary wakefulness. While Whoop has been validated by independent studies, including one published in the Journal of Clinical Sleep Medicine, some users have shared their experiences of inconsistent sleep tracking, especially when there is wrist movement or when the strap fit is loose. Overall, Whoop offers valuable insights into sleep quality and duration, but individual experiences may vary, and factors such as skin colour or tattoos can also impact the accuracy of heart rate measurements.

Characteristics Values
Accuracy of REM sleep tracking Accurate according to some users; inaccurate according to others
Heart rate tracking accuracy Accurate when there isn't a lot of wrist movement; less accurate during exercises with lots of wrist movement
Calorie burn accuracy Unable to accurately predict absolute calorie burn; can accurately record relative changes in calories burned
Strain tracking accuracy Depends on an accurate heart rate reading; certain types of physical activities cause slightly inaccurate strain scores
Sleep tracking accuracy Accurate according to third-party validation studies; excellent agreement with EKG

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Whoop's accuracy in tracking REM sleep

The accuracy of Whoop in tracking REM sleep has been validated by independent studies, including one conducted by the University of Arizona, which was published in the Journal of Clinical Sleep Medicine. The study found that Whoop was highly accurate when compared to polysomnography (PSG), the gold standard of sleep tracking.

Whoop collects hundreds of data points per second using its accelerometer, gyroscope, and PPG heart rate sensor. It uses photoplethysmography (PPG) to measure blood flow by assessing changes in blood volume. By shining specific colours of light onto the skin and measuring the light reflected back, Whoop can derive heart rate, heart rate variability, and respiratory rate, which are used in its sleep detection and staging algorithms.

The University of Arizona study found that Whoop's sleeping respiratory rate algorithm was within 1 breath per minute of the gold standard, and its sleeping heart rate was within 1 beat per minute of an EKG. It also showed highly accurate detection of REM and Slow Wave (deep) sleep.

Another study of leading wrist-worn wearables revealed that Whoop was the most accurate when compared to PSG. However, it is important to note that Whoop may struggle to differentiate between light sleep and sedentary wakefulness, as this differentiation is typically done through human interpretation of EEG readings and visual observation, which Whoop cannot do.

Overall, Whoop has been shown to be highly accurate in tracking REM sleep, but it may have limitations in distinguishing between light sleep and wakefulness in certain scenarios.

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Whoop's limitations during certain activities

While Whoop is highly accurate in tracking sleep and sleep stages, it has limitations during certain types of activities and workouts, especially those involving a significant amount of wrist movement.

Whoop relies on light-emitting diodes (LEDs) that shine light through your skin and onto your blood vessels. Interpreting the light signal as it bounces back from your skin is an analog process, and is thus subject to interference and signal noise. This means that any activity that involves wrist movement can cause issues with the accuracy of the data. For example, during CrossFit or other types of high-intensity interval training (HIIT), your heart rate changes a lot, and the sensor may lose contact with your skin.

Other factors that can negatively impact the accuracy of Whoop during activities include:

  • A loose strap that doesn't have sufficient contact between the sensor and the skin.
  • Body motion that the sensor might interpret as heart contractions.
  • Ambient and body temperature, which influence blood flow.
  • Variables that can interfere with the reading of the reflected light, such as skin colour or tattoos.

To mitigate these issues, Whoop has released accessories like the SuperKnit strap, which provides a more secure and comfortable fit, and Whoop Body, a special line of activewear that enables you to wear the sensor on your arm or hip.

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Whoop's heart rate variability (HRV) tracking

Whoop Heart Rate Variability (HRV) Tracking

Heart rate variability (HRV) is a measure of the variance in time between each heartbeat. The higher the variability is, the more ready your body is to perform. HRV is a valuable indicator for potential illness and fitness.

The Whoop band is one of the few sensors that complies with the standard Bluetooth heart-rate profile. This means that you can link the band to any other third-party app for heart rate and HRV analysis. This is useful because, if the data is accurate, we can use the sensor as a replacement for a chest strap to collect morning HRV data.

A study funded by the Australian Institute of Sport (AIS) found that Whoop was 99.7% accurate in measuring heart rate and 99% accurate in measuring HRV—levels of accuracy that surpassed all other wearables in the study. Another study of leading wrist-worn wearables revealed that Whoop was the most accurate when compared to the gold-standard PSG.

Whoop's former approach to night HRV was flawed from a physiological and technological perspective. Last summer, Whoop aligned with Oura and now reports the full night of HRV (with a different "weighting", but data shows that they are now an almost perfect match).

In a third-party study, Whoop was shown to be highly accurate in measuring HRV. The study found that Whoop had the smallest errors in measurement with a standard deviation in data of 1 beat per minute (bpm) while other wearables ranged from 2.1 to 12.8 bpm.

The Whoop Health Monitor displays key vital signs and lets you see if they are within their normal ranges.

Whoop collects hundreds of data points per second using the device's accelerometer, gyroscope, and PPG heart-rate sensor. PPG, or photoplethysmography, is a technique that involves measuring blood flow by assessing superficial changes in blood volume. When you shine specific colours (wavelengths) of light onto the skin, blood volume can be measured by looking at the light reflected back from our skin since blood absorbs specific colours and reflects others. Once blood flow is measured, we can then derive heart rate, HRV, and respiratory rate, all of which are used in Whoop's sleep detection and staging algorithms.

Whoop's Limitations

You might experience mixed results with heart rate tracking during certain types of exercises and activities, especially when they involve lots of wrist movement. Factors that can negatively influence the accuracy of Whoop include:

  • A loose strap that has insufficient contact between the sensor and the skin.
  • Wrist movement that temporarily breaks contact between the sensor and your skin.
  • Body motion that the sensor might interpret as heart contractions.
  • The ambient temperature and your body temperature, both of which influence blood flow.
  • Variables that can interfere with the reading of the reflected light (e.g. your skin colour or tattoos).

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Whoop's sleep staging algorithm

WHOOP collects hundreds of data points per second using its accelerometer, gyroscope, and PPG heart rate sensor. It also measures capacitive touch and temperature but does not use data from these sensors in its sleep algorithm. PPG, or photoplethysmography, is a technique that involves measuring blood flow by assessing superficial changes in blood volume. The tiny green lights on the bottom of the WHOOP strap are part of this process, which also involves a photo-receptor that measures light. By shining specific colours (wavelengths) of light onto the skin and observing the differences in light, WHOOP can track changes in blood flow caused by each pulse and calculate heart rate and heart rate variability.

The University of Arizona conducted an independent validation of WHOOP's sleep staging analytics, published in the Journal of Clinical Sleep Medicine. This study found that WHOOP was highly accurate when compared to PSG, the gold standard of sleep tracking. Specifically, the study found that WHOOP's sleeping respiratory rate algorithm was within 1 breath per minute of the gold standard, and its sleeping heart rate was within 1 beat per minute of an EKG. WHOOP sleep staging also had high levels of agreement with PSG testing.

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Whoop's recovery score

The WHOOP Strap is a 24/7 fitness tracker that helps users understand how their bodies function and change over time. One of its key features is its recovery analysis, which calculates a daily recovery score as a percentage between 0-100%. This score is a reflection of how the user's nervous system is doing and is calculated by measuring heart rate variability (HRV) during the last phase of deep sleep. This is when the brain is most "disconnected" from the rest of the body, preventing movement or other influencing factors.

The recovery score is colour-coded into three categories: green (67-100%), yellow (34-66%), and red (0-33%). A green score indicates that the user is well recovered and primed to perform strenuous activity. A yellow score suggests that the body can handle a moderate amount of strain, while a red score means that rest is likely what the body needs as it is working hard to recover. The average recovery score for WHOOP members is approximately 58%.

The recovery score is influenced by several physiological metrics, including HRV, resting heart rate (RHR), respiratory rate, sleep performance, blood oxygen level, and skin temperature. HRV is the biggest influence on the score, but health, behaviours, stress levels, and hydration are also considered. The score is intended to guide users in making decisions about their daily activity levels. For example, if a user has a red recovery score, they may decide to take it easy that day, whereas a green score may indicate that it is a good day to engage in strenuous activity.

The recovery score is highly accurate, with third-party validation studies confirming WHOOP's accuracy as a sleep tracker. A study funded by the Australian Institute of Sport (AIS) found that WHOOP was 99.7% accurate in measuring heart rate and 99% accurate in measuring HRV when compared to electrocardiogram-derived (ECG) metrics. Another study by the University of Arizona found that WHOOP accurately detects sleep duration with a precision of 17.8 minutes and also reported highly accurate detection of REM and Slow Wave (deep) sleep.

Frequently asked questions

WHOOP has been proven to be highly accurate in tracking sleep. The University of Arizona conducted an independent validation of WHOOP's sleep staging analytics, which was published in the Journal of Clinical Sleep Medicine. The study found that WHOOP was highly accurate when compared to polysomnography (PSG), the gold standard of sleep tracking.

WHOOP collects hundreds of data points per second using its accelerometer, gyroscope, and PPG heart-rate sensor. It measures blood flow by assessing superficial changes in blood volume using PPG (photoplethysmography). WHOOP then derives heart rate, heart rate variability, and respiratory rate, which are used in its sleep detection and staging algorithms.

WHOOP tracks four stages of sleep: slow-wave sleep (SWS), REM, light, and awake. Each stage serves a different purpose in the recovery process. Slow-wave sleep is the physically restorative stage, while REM is the mentally restorative stage.

Tracking sleep is crucial for understanding your body's recovery and performance. Decades of research have shown that sleep is essential for recovery, performance, and overall health. WHOOP's sleep analytics provide insights into your sleep duration, quality, and patterns, enabling you to make informed decisions to optimize your sleep and enhance your recovery.

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