Home Insights Smartwatch Fitbit Sleep Tracker Accuracy: What you should know

Fitbit Sleep Tracker Accuracy: What you should know

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According to Mordor Intelligence, the global smartwatch market for 2026 will reach more than 230 million units, a staggering CAGR of 22% during the 2021 to 2026 period. 

People buy smartwatches or fitness trackers for numerous reasons, far from just knowing what the time is. With smartwatches and fitness trackers becoming fashion accessories, health powerhouses, and fitness or diet coaches, there are plenty of reasons to wear a smart device on your wrist.

One of them may be to analyze your sleep to know more about your sleeping patterns or get into a healthy bedtime routine that translates into better and more productive days.

Actually, according to an article published on T3.com, the first three reasons why people bought a smartwatch were:

  1. Track their daily activities,
  2. Measure the heart rate and
  3. Improve sleep.

Sleep issues affect a large percentage of the population. They impact up to 70 million people in the United States every year. On average, 1 in 2 adults has insomnia symptoms, and 1 in 10 struggle with chronic sleep disorders. 

Numerous devices have hit the market promising detailed sleep patterns analyses leading to better sleep in recent years.

From sleep tracking mats to smart pillows and portable electroencephalograms, such as the Muse, up to high-end sleep trackers. 

How does Fitbit track sleep?

The Fitbit wearables have been extremely popular among consumers, with more than 28 million active users and 60 million devices in more than 80 countries.

Fitbit smartwatches and fitness trackers include up to 16 sensors. Yes, you read well: 16 divided into 3-axis accelerometers, gyroscopes, altimeter, electrocardiogram, electrodermal activity sensor, thermic sensor, blood oxygen saturation sensor, and of course, a multi-path optical heart rate tracker.

Packed with so much technology, Fitbit devices offer the possibility to track much more than just the time you sleep. It can also dissect your resting time into various sleep stages, including light sleep, deep sleep, and REM sleep, during which we dream.

In just 40 years, technology evolved dramatically to detect sleep patterns and assess sleep quality. 

In the 1980s, Ambulatory Monitoring Inc. created a wrist actigraphy device that detected rapid motion. Today, the technology is used in conjunction with proprietary algorithms to conduct outpatient sleep exams, which results in the estimate of essential sleep metrics.

Fitbit launched its first wearable device nearly ten years ago to benefit health-conscious customers. Besides its many sensors, the device also relies on algorithms that have been calibrated using the gold standard polysomnography to detect the various stages of sleep by recognizing brain wave patterns.

What can you learn from the Fitbit Sleep Score?

The Sleep Score is at the center of the Fitbit sleep tracking analysis. By integrating various parameters such as time spent in the various stages, heart rate, and movements, the algorithms will compute a score that reflects your sleep quality.

The length of time spent sleeping is a crucial component. The more hours slept, the better the score. 7 to 8 hours of sleep every night is the minimum time advised. If you can sleep inside this range, you will receive bonus points.

The sleep cycle is divided into three phases: light sleep, deep sleep, and rapid eye movement sleep (REM). Deep sleep and rapid eye movement (REM) sleep phases are the most beneficial for recovery, and the more time spent in these two cycles, the better the score.

The higher the restorative sleep score, the more restful the night’s sleep. With the sleep monitoring function, you may measure your heart rate and movements to determine the quality and restoration of your sleep. 

The tracker will assess the sleep pattern, including the time spent in light or deep sleep, and link it with the heart rhythm to determine the average sleeping heart rate. This information is critical because a better restoration score will be granted to the individual if the sleeping heart rate is lower than the average day heart rate.

Individuals will receive a score ranging from 0 to 100 that combines the individual scores of the various component components. Most healthy sleepers will fall between 70 and 80 minutes every night.

We do not know if the Fitbit Sleep Score is scientifically accurate, but we can say that we feel more rested when our sleep score is higher.

What does Science say about Fitbit Sleep Tracker Accuracy?

In 2019, Haghayegh et al. from the University of Austin, Texas conducted a meta-analysis of the scientific publications dealing with the sleep tracking accuracy of the Fitbit Smartwatches and Fitness Trackers.

The criteria to select the articles to be included were strict: The data needed to include:

– Polysomnography, actigraphy, home electroencephalogram, or a detailed sleep diary

Out of 3085 candidate articles, 22 were deemed acceptable, including a systematic review, while eight also presented quantitative data.

The researchers examined both nonsleep-staging and sleep-staging Fitbit models. The research found that the advanced body movement and heart rate variability approach used by recent-generation Fitbit wristband models appears acceptable for obtaining accurate estimations of sleep characteristics and time spent asleep, despite these limitations. 

The findings also show that Fitbit models may be valuable in conducting population-based sleep research.

According to additional research, the Fitbit Ionic and the Oura Smart Ring were found to have the lowest degrees of error in sleep tracking compared to an electroencephalography (EEG)-based device and other wrist-based trackers published in the Nature & Science of Sleep Journal in October 2020.

How does Fitbit compare to the other sleep trackers?

As far as sleep tracking is concerned, Fitbit wearables are a solid choice. According to a review conducted by Wareable.com the Fitbit Sense and Fitbit Charge 5 are the best sleep tracking devices available.

We could not agree more. Be careful to wear your device relatively tightly for the sensors not to move during your sleep and for the collected data to stay accurate.

An issue we also experienced numerous times while using the Fitbit Charge 5 to track our sleep is the lack of Blood Oxygen Tracking. This can be incredibly annoying as this value is of interest to detect sleep apnea episodes potentially. 

Fitbit does not claim that any of its trackers can detect sleep apnea, but it makes perfect sense to use the levels of oxygen variation during the night to understand what is going on while you sleep.

One of the drawbacks of the Fitbit Sleep Score is the need to pay for a Premium subscription ($9.99 per month). The business model of wearable devices is evolving. The hardware is getting more affordable. Fees need to be paid monthly or yearly to benefit from more accurate analyses. A smartwatch or fitness tracker is slowly becoming a Software As A Service (SAAS). We do not like this model, but there is, unfortunately, no choice but to pay to continue benefiting from accurate analyses.

With devices becoming more powerful and with a shortening lifecycle, this subscription model makes sense for the manufacturers but can be a tough pill to swallow for most users.

In conclusion

Personal monitoring technology is quickly improving in terms of both quality and applications, and it holds the possibility of a significant advance in medical literacy and health. 

Consumers and health experts are increasingly concerned about the quality of their sleep, which has been shown to impact their daytime cognitive and physical function significantly. 

Many wrist-worn gadgets are available to track sleep characteristics and periods.

According to preliminary analyses, Fitbit’s sleep sensitivity appears to be compatible with the research on the 24-hour sleep-wake cycle and the length, pattern, and quality of sleep over a long time, such as several consecutive nights in a typical living environment. 

Individuals can benefit from the information gathered by wristband trackers in this respect, as it can help them improve their sleep hygiene and overall sleep quality. In addition, in certain circumstances, general care physicians and sleep experts can at the very least get a rudimentary understanding of their patients’ sleep patterns. 

However, even though there has not yet been a sufficient evaluation of recent-generation Fitbit sleep-staging models, preliminary findings from the few published studies that have been conducted so far suggest that their performance in distinguishing between wake and sleep epochs is superior to that reported in the literature for actigraphy.

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