Herbie Murray
The Apple Watch's Sleep app can estimate the time spent in different sleep stages, categorising sleep into core, deep, and REM sleep. Deep sleep is the middle stage of each sleep cycle and is also known as N3 sleep. The Apple Watch uses an accelerometer, heart rate sensor, and blood oxygen sensor to approximate sleep stages, but this method cannot easily distinguish between N1 and N2 sleep, which are combined into core sleep. The average Apple Watch user achieves 49 minutes of deep sleep per night, which is around 12-13% of their total sleep time.
| Characteristics | Values |
|---|---|
| Sleep stages | Core, Deep, and REM |
| Deep sleep | N3 |
| Average deep sleep | 49 minutes per night |
| Percentage of total sleep time | 12-13% |
| Good deep sleep | 14% or higher |
| Top 10% of sleepers | 18% of total sleep time spent in deep sleep |
| Bottom 10% of sleepers | 28 minutes of deep sleep per night |
| Top 10% of sleepers | 71 minutes of deep sleep per night |
| Accuracy | 62% |
| Core sleep | Light sleep (N1 and N2) |
| REM sleep | Deep sleep |
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What You'll Learn
How Apple Watch tracks sleep
The Apple Watch can track sleep using the Sleep app. The watch uses its accelerometer, heart rate sensor, and blood oxygen sensor to approximate sleep stages. It categorizes sleep into three categories: core, deep, and REM. These categories are based on the sleep cycle, which lasts about 90 minutes and consists of four stages. The Apple Watch combines stages N1 and N2 into core sleep, N3 into deep sleep, and the final stage into REM sleep.
The Apple Watch can help users set sleep schedules and sleep goals. It can also provide a bedtime reminder and turn on Sleep Focus, which limits distractions before bedtime. The watch can also track the user's movement to detect sleep, although it requires the user to be awake for several minutes to register that they are no longer asleep.
The watch can estimate the time spent in each sleep stage and provide a summary of sleep trends over the past 14 days. It can also detect when the user wakes up during the night. However, it is important to note that the Apple Watch may not always accurately distinguish between sleep stages, particularly between core and deep sleep. The watch may also struggle to detect when the user is awake, especially if they are moving very little.
The data provided by the Apple Watch can be viewed in the Sleep app or the Health app on the iPhone. The user can also download third-party apps, such as Empirical Health, to access more detailed sleep data and benchmarks. These apps can provide insights into sleep duration, onset time, quality, sleeping oxygen, heart rate, and more. They can also help identify potential causes of poor sleep, such as sleep apnea.
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Deep sleep as a percentage of total sleep
The Apple Watch divides sleep into three categories: core, deep, and REM. These categories are based on the sleep cycle, which consists of four stages and repeats throughout the night. N1 and N2 correspond to core sleep, while N3 corresponds to deep sleep. REM is the fourth stage.
Deep sleep is the middle stage of each sleep cycle and makes up about 12% of total sleep time on average for Apple Watch users, according to Empirical Health. However, there is a lot of variance, and some users report getting up to 1 hour and 21 minutes of deep sleep per night. The Apple Watch approximates sleep stages based on its accelerometer, heart rate sensor, and blood oxygen sensor, but it cannot easily distinguish between N1 and N2, so they are combined into core sleep.
According to Empirical Health, if you spend 14% or more of your total sleep time in deep sleep, you are in the top 10% of sleepers. However, it's important to note that the Apple Watch may not always accurately distinguish between core and deep sleep, with an accuracy rate of around 62%.
The Sleep app on the Apple Watch allows users to track their sleep and set sleep schedules to help them meet their sleep goals. It can estimate the time spent in each sleep stage and provide sleep trends over the past 14 days. Additionally, the Wind Down feature helps users create a bedtime routine and reduce distractions before bedtime.
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Accuracy of Apple Watch deep sleep tracking
Sleep is divided into cycles throughout the night, N1, N2, N3, and REM. N1 and N2 correspond to Core sleep, and N3 corresponds to deep sleep on Apple Watch. The gold standard for measuring sleep stages in a laboratory setting is an EEG (electroencephalogram), a device worn on the head to detect brain waves. However, Apple Watch uses its accelerometer, heart rate sensor, and blood oxygen sensor to approximate sleep stages.
The Apple Watch sleep tracking feature has been tested for accuracy in a study of 166 people who wore both an Apple Watch and polysomnography equipment. The study found that the Apple Watch was about 62% accurate in detecting deep sleep, mistaking it for core sleep 38% of the time. This means that the Apple Watch is likely to underestimate deep sleep.
Other sources suggest that the Apple Watch is about 85% accurate in detecting deep sleep, which is higher than the accuracy of other wrist trackers. However, it is important to note that the accuracy of sleep tracking can vary between individuals and that there may be a degree of discrepancy between the Apple Watch and other sleep tracking applications.
The Apple Watch sleep tracking feature provides insights into sleep stages, sleep duration, onset time, quality, sleeping oxygen, heart rate, and more. It also helps identify potential causes of poor sleep, such as sleep apnea, and provides recommendations for improving sleep hygiene.
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How to interpret deep sleep data
The Apple Watch divides your sleep into three categories: core, deep, and REM. These categories are based on the well-known sleep cycle, where each night's sleep is divided into cycles that last about 90 minutes, and each cycle has four stages. The Apple Watch creates an approximation based on its accelerometer, heart rate sensor, and blood oxygen sensor.
Deep sleep is the middle stage of each sleep cycle. According to Apple Watch data, the average deep sleep is 12% of total sleep, or about 49 minutes per night. However, there is a lot of variance, and if you spend 18% of your total sleep time in deep sleep, you are in the top 10% of sleepers.
It's important to note that the Apple Watch algorithm can sometimes miscategorize light sleep as deep sleep or vice versa. This means that your watch may underestimate or overestimate the amount of deep sleep you are getting. Therefore, it is recommended not to make any significant changes to your routine based on the specific sleep stage numbers.
To interpret your deep sleep data, you can use the metrics screen in the Empirical Health app, which is designed to help you benchmark your sleep data. This includes sleep duration, onset time, quality, sleeping oxygen, heart rate, and more. You can also compare your deep sleep data to others within the metrics screen. Additionally, the Sleep app on Apple Watch can help you track your sleep and set sleep schedules to meet your sleep goals.
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Improving deep sleep
The Apple Watch can help you improve your deep sleep by tracking your sleep and providing insights into your sleep patterns. Here are some ways you can use the Apple Watch to improve your deep sleep:
Set Sleep Goals and Schedules
The Health app on your iPhone, when paired with your Apple Watch, allows you to set sleep goals and create customized sleep schedules. You can determine the number of hours you want to sleep and set your preferred bedtime and wake-up times. This helps you develop a consistent sleep routine, which is essential for improving sleep quality.
Enable Sleep Focus
The Sleep Focus feature on your Apple Watch and iPhone helps reduce distractions before your scheduled bedtime. It simplifies your Lock Screen and limits notifications to create a calm environment conducive to better sleep.
Track Sleep Stages
The Apple Watch categorizes your sleep into three stages: Core sleep (N1 and N2), Deep sleep (N3), and REM sleep. By tracking these stages, you can understand your sleep quality and identify areas for improvement. The watch approximates your sleep stages based on its accelerometer, heart rate sensor, and blood oxygen sensor.
Analyze Sleep Trends
The Sleep app on your Apple Watch and iPhone provides insights into your sleep trends over time. You can view your sleep history for the past week, month, or even six months. This helps you identify patterns and make informed decisions to improve your deep sleep.
Monitor Respiratory Rate
The Apple Watch can track your breathing rate during sleep, providing insights into your overall health. A low respiratory rate during sleep may indicate good sleep quality. However, consult a healthcare professional for accurate interpretations of your respiratory data.
Identify Sleep Apnea
The latest Apple Watch models can alert you to possible sleep apnea, a condition where your breathing stops during sleep. If you receive such alerts, consider taking an at-home sleep apnea test or consulting a healthcare professional for further guidance.
By utilizing these features of the Apple Watch and making necessary adjustments to your sleep habits, you can work towards improving the quality of your deep sleep. Remember that getting enough sleep and maintaining a consistent sleep schedule are crucial for your overall health and well-being.
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Frequently asked questions
Deep sleep is the middle stage of each sleep cycle. The Apple Watch divides sleep into three categories: core, deep, and REM. Deep sleep is also known as N3 sleep.
The average Apple Watch user gets 49 minutes of deep sleep per night, which is about 13% of their total sleep time.
The Apple Watch was about 62% accurate in detecting deep sleep, mistaking it for core sleep 38% of the time. This means your Apple Watch is likely to underestimate deep sleep.
