Alta's Sleep Tracking: Unlocking The Science Of Sleep

Fitbit's Alta HR is a $150 fitness tracker that monitors sleep. It has a heart rate monitor that tracks sleep stages by measuring slight fluctuations in heart rate. The Alta HR also has a microphone that can track snoring and noise levels. The device is worn on the wrist and uses actigraphy to track sleep, which means it tracks sleep based on movement. However, this method of tracking sleep can be inconsistent and is not as accurate as polysomnography (PSG), which is considered the gold standard for measuring sleep.

Alta HR's sleep tracking

Fitbit's Alta HR is a slim fitness tracker that can be worn on the wrist to monitor sleep. It is an upgrade to the original Alta and includes a heart rate monitor on the underside to provide more detailed sleep analysis. The Alta HR uses actigraphy, a method of tracking sleep by monitoring movement, to estimate sleep cycles and determine the length of time spent in different sleep stages. This involves tracking periods of restlessness and overall sleep duration. The device also uses a microphone to track noise levels and check for snoring.

To use the Alta HR for sleep tracking, the device should be worn securely on the wrist during sleep. Fitbit recommends wearing the device in a snug wristband, positioned higher on the wrist, about 2-3 finger widths above the wrist bone. The band should be tight enough to prevent the device from moving out of position during sleep, which could result in the loss of heart rate data and inaccurate sleep tracking.

The Alta HR's sleep tracking feature provides a detailed breakdown of sleep behaviour, including the time spent awake, restless, and asleep. It also offers a monthly sleep profile with 10 metrics and a sleep animal characterisation. However, the accuracy of the sleep tracking has been questioned, particularly in individuals with disrupted sleep patterns or those who sleep in certain positions that may hinder the device's ability to detect heart rate.

While the Alta HR's sleep tracking feature provides insights into sleep patterns, it is important to note that it is not intended to diagnose or treat medical conditions related to sleep. For more advanced sleep analysis, polysomnography (PSG) in a sleep lab is considered the "gold standard" by sleep researchers.

Accuracy of sleep tracking

The accuracy of sleep tracking varies depending on the device and the individual. Sleep researchers use polysomnography (PSG) to study sleep in a lab, which is considered the "gold standard" for measuring sleep. PSG involves monitoring brain waves through an EEG test, which is more accurate but less convenient than other methods.

Actigraphy, on the other hand, is a method used by many sleep-tracking devices, including the Fitbit Alta HR, to track sleep by measuring movement. While actigraphy is generally accurate for healthy adults with "normal" sleep patterns, it may be less accurate for those with disrupted sleep or sleep disorders. This is because actigraphy only tracks movement, while sleep researchers emphasize the importance of also measuring brain waves and eye movements to assess sleep phases accurately.

The Fitbit Alta HR incorporates heart-rate data into its algorithms to estimate sleep states, which is an improvement over previous versions that only measured movement. However, the device still relies primarily on movement to track sleep, which can lead to inconsistencies. For example, the Alta HR may fail to track sleep stages if the battery level is low or if the user's arm shifts into a position that prevents the device from getting a consistent heart rate reading.

To improve the accuracy of sleep tracking with the Fitbit Alta HR, it is recommended to wear the device snugly on the wrist, ensure the battery is charged, and avoid sleeping in positions that may hinder the device's ability to get a consistent heart rate reading. While the Alta HR provides insights into sleep patterns, it is important to note that it is not a substitute for medical diagnosis or treatment of sleep-related conditions.

Heart rate monitoring

The Alta HR by Fitbit is a fitness tracker that monitors sleep. It has a heart rate monitor on the underside of the device that constantly keeps tabs on the user's pulse. This heart rate data is incorporated into the device's algorithms to estimate what sleep state the user is in. The Alta HR's sleep tracking feature works by detecting the user's heart rate to estimate their sleep cycles. If the device is unable to detect the user's heart rate, it may not be able to provide sleep stage information. The device also has a snore and noise detection feature that allows the microphone on the device to track noise while the user sleeps. This feature can be turned on in the Fitbit app.

The Alta HR's heart rate monitor is an optical heart rate monitor that measures slight fluctuations in the user's heart rate to determine their sleep stages. The device uses this data to provide a deeper analysis of the user's sleep, including the duration of slumber and periods of restlessness. The user can view their sleep data in the Fitbit app, which includes information about their time spent awake, restless, and asleep.

To ensure accurate sleep tracking, the user should wear the device securely around their wrist, with the band feeling snug but not too tight. The device should be positioned higher on the wrist, about 2-3 finger widths above the wrist bone. It is also recommended to wear the device to bed, as the Fitbit automatically detects sleep when the user wears it to bed. If the user does not wear the device to bed, they can manually sync their device to track their sleep.

While the Alta HR's sleep tracking feature is generally considered to be accurate, some reviewers have noted inconsistencies in the data. The device may not be able to provide sleep stage information if the user sleeps for less than three hours or if the battery level is critically low. Additionally, the device may not be able to detect the user's heart rate if it is worn too loosely or if the user's arm shifts during sleep, which can affect the accuracy of the sleep data.

Actigraphy

However, actigraphy has limitations. It primarily tracks movement, and its accuracy decreases with more disrupted sleep patterns. It does not measure brain activity (EEG), eye movements (EOG), muscle activity (EMG), or heart rhythm (ECG), which are important for assessing sleep phases and making accurate diagnoses. As a result, actigraphy is not considered a substitute for PSG, especially in cases of certain sleep disorders where a full night of PSG data may be required.

Despite its limitations, actigraphy has been actively used in sleep research since the early 1990s. Technological advancements in actigraph hardware and software have improved its accuracy, with some studies reporting accuracy above 90% for estimating total sleep time. Actigraphy is particularly advantageous for large field studies due to its affordability and convenience.

Snore and noise detection

The Alta HR is Fitbit's latest wearable device, which incorporates heart-rate data into its algorithms to estimate what sleep state the user is in. The Alta HR has a new heart rate monitor on its underside that constantly keeps track of the user's pulse. The Alta HR also has a narrower footprint than Fitbit's flagship Charge tracker, making it look more like a bangle than a cuff.

The snore and noise detection feature on the Fitbit Alta HR allows the device's microphone to track noise while the user sleeps. The microphone on the device analyses noise information every few seconds, tracking the overall noise level of the surroundings and checking for snoring throughout the night. The nightly results are summarised in a report that can be accessed via the Fitbit app. To enable the feature, open the Fitbit app, tap the Sleep duration tile on the Today tab, and turn on Snore & Noise Detect in the Settings menu.

It is important to note that the snore and noise detection feature does not analyse previous nights' sleep, and it is recommended to not play white noise or other ambient sounds during sleep as they may interfere with the accuracy of the results. Additionally, wearing the device snugly on the wrist during sleep is recommended for optimal tracking.

While the Alta HR's sleep-tracking feature works well most of the time, there have been some inconsistencies noted in reviews. For example, the sleep-tracking chart may only include movement-based data about how long the user has been awake, restless, and asleep, without any information on sleep stages. Fitbit has explained that this could be due to several reasons, such as sleeping for less than three hours or having a critically low battery level. Additionally, the tracker needs to detect the user's heart rate to estimate sleep cycles, so wearing the device too loosely or sleeping in a position that prevents a consistent heart-rate reading may affect the accuracy of the results.

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