Understanding Fitbit Charge 2: Tracking Rem Sleep

The Fitbit Charge 2 is a multisensor, consumer-grade device that can be used to track sleep. It measures wrist activity using accelerometry and pulses via photoplethysmography. The device has two types of sleep data: classic and stages. The classic data type includes sleep, awake, and restless variables at a 1-minute data granularity, while the stages data type includes wake, light, REM, and deep sleep at a 30-second data granularity.

The Fitbit Charge 2 has been validated against polysomnography (PSG), the gold standard for sleep measurement, in several studies. These studies have shown that the device can provide reasonably accurate estimates of sleep variables such as sleep onset, sleep offset, total sleep time, and the duration of REM sleep. However, there are some limitations to the device's accuracy, including a tendency to overestimate REM sleep latency and wakefulness after sleep onset. Overall, the Fitbit Charge 2 can be a useful tool for tracking sleep, but it may not be suitable for addressing clinical or research questions without further validation.

Fitbit Charge 2 may not show REM sleep due to the device's sleep sensitivity setting

The Fitbit Charge 2 may not show REM sleep due to the device's sleep sensitivity setting. The sleep sensitivity setting on the Fitbit Charge 2 allows users to set the device to track sleep in either "normal" or "sensitive" mode. In normal mode, only significant movements, such as rolling over, will be recorded as awake time. This setting is suitable for most users. However, in sensitive mode, the device will record almost all movements as restless or awake time. This setting may be useful if you wake up feeling tired, even though your sleep history shows sufficient rest.

The sleep sensitivity setting can be adjusted in the Fitbit app. To change the setting, open the app and go to the "Today" tab. From there, tap your profile picture and select "Fitbit settings." In the "Preferences" section, tap "Sleep" and then "Sleep Sensitivity." You can then choose between normal and sensitive mode.

It's important to note that the sleep sensitivity setting does not affect the detection of sleep stages, including REM sleep. The detection of sleep stages is based on movement and heart rate patterns. When you haven't moved for about an hour, the Fitbit Charge 2 assumes you're asleep. It also uses heart rate variability to distinguish between light sleep, deep sleep, and REM sleep.

If you're not seeing REM sleep stages on your Fitbit Charge 2, there could be other reasons. Ensure that your device's battery is not critically low and that it is syncing properly with the Fitbit app. Additionally, make sure you're wearing the device snugly on your wrist, about 2-3 finger widths above your wrist bone. Wearing the device too loosely can affect the accuracy of sleep tracking.

Another reason you may not be seeing REM sleep stages is if you slept for less than 3 hours. The Fitbit Charge 2 requires at least 3 hours of sleep data to estimate sleep stages. Additionally, if you recently updated your Fitbit app, the REM sleep feature may not have rolled out to your device yet. Fitbit states that the REM sleep feature will arrive at some point, but they have not provided a specific timeline.

Fitbit Charge 2 may not show REM sleep if the user slept in a position that prevented the device from getting a consistent heart-rate reading

The Fitbit Charge 2 is a multisensor, consumer-grade device that can be used to track sleep quality. It does this by measuring sleep stages and heart rate. However, for the device to work effectively, it needs to be able to get a consistent heart-rate reading. If you sleep in a position that prevents this, such as with your arm under your body, the device may not show REM sleep.

To get the most accurate reading from your Fitbit Charge 2, it is recommended that you wear the device higher on your wrist, around 2-3 finger widths above your wrist bone. The band should be secure but not too tight. You should also avoid wearing the device too loosely as this can also affect the reading.

If you are still having issues with your Fitbit Charge 2 not showing REM sleep, there are a few other things you can try. Firstly, make sure you are wearing the device to bed and not using the "Begin Sleep Now" option in the Fitbit app. Additionally, the device needs at least 3 hours of sleep data to estimate your sleep stages, so if you slept for less than this, you won't receive any information on your sleep stages. Finally, check that your device's battery isn't critically low, as this can also affect the reading.

Fitbit Charge 2 may not show REM sleep if the user wore the device too loosely

The Fitbit Charge 2 is a multisensor, consumer-grade device that can be used to objectively collect rest-activity data longitudinally under ambulatory conditions. It is a cost-efficient, practical, and convenient means of monitoring sleep quality. However, the accuracy of Fitbit technology remains a major concern for medical professionals and the lay public.

For best results, wear your Fitbit device higher on your wrist (about 2-3 finger widths above your wrist bone). The band should feel secure but not too tight. If you sleep in a position that prevents your device from getting a consistent heart-rate reading or you wear it too loosely, you might only see your sleep pattern (which shows your time asleep, restless, and awake) instead of sleep stages.

Fitbit Charge 2 may not show REM sleep if the user slept for less than 3 hours

The Fitbit Charge 2 is a multisensor, consumer-grade device that can be used to objectively collect rest-activity data longitudinally under ambulatory conditions. It has the potential to be a cost-efficient, practical, and convenient means of monitoring sleep. However, for it to be useful for clinical and research purposes, multisensor wearables such as the Fitbit Charge 2 require careful validation against the gold standard of sleep polysomnography (PSG).

Fitbit Charge 2 uses accelerometry and photoplethysmography to record wrist activity and pulses, respectively. It produces two types of sleep data: classic and stages. Classic data are generated when certain criteria (e.g. sufficient battery charge, sleep episode >3 hours) are not fulfilled and include asleep, awake, and restless variables at a 1-minute data granularity. Stages data are produced when the criteria are fulfilled and include wake, light, REM, and deep sleep variables at a 30-second data granularity.

A study by de Zambotti et al. (2018) found that the Fitbit Charge 2 displayed a 9-minute overestimation of total sleep time (TST) and an underestimation of sleep onset latency by 4 minutes when compared to PSG. The same study also found that Fitbit's light stage was overestimated by 34 minutes, and deep sleep stage was underestimated by 24 minutes compared to PSG-derived sleep stages N1+N2 and N3, respectively.

Another study by Liang and Chapa Martell (2018) compared Fitbit Charge 2 with a portable single-channel electroencephalogram sleep monitor. This study showed 86.9% agreement but found an underestimation of TST by 12.3 minutes, of light sleep by 42.4 minutes, and of REM sleep by 11.6 minutes. Conversely, wake after sleep onset (WASO) was overestimated by 24.5 minutes and deep sleep by 39.8 minutes.

A naturalistic study by Stucky et al. (2021) in a sample of first responder shift workers found unbiased estimates of sleep onset, sleep offset, TST, REM sleep duration, light sleep duration, and deep sleep duration with non-negligible limits of agreement. However, the proprietary Fitbit algorithm overestimated REM sleep latency by 29.4 minutes and WASO by 37.1 minutes. Epoch-by-epoch analyses indicated better specificity than sensitivity, with higher accuracies for WASO and REM sleep than for light and deep sleep.

In summary, the Fitbit Charge 2 can provide reasonably accurate mean values of sleep estimates in shift workers under naturalistic conditions. However, the wide limits of agreement and large biases in some variables may limit the precision of quantifying individual sleep episodes. The value of this consumer-grade multisensor wearable in addressing clinical and research questions could be enhanced with open-source algorithms, raw data access, and the ability to blind participants to their own sleep data.

Fitbit Charge 2 may not show REM sleep if the device's battery is critically low

To check if your Fitbit Charge 2's battery is critically low, you can refer to the device's battery level indicator. If the battery is critically low, you may need to charge your device before using it to track your sleep.

It is important to note that there could be other reasons why your Fitbit Charge 2 may not be showing REM sleep. For example, if you did not wear the device correctly or if you did not wear it to bed, the device may not have been able to track your sleep accurately. Additionally, if you slept for less than 3 hours, the Fitbit Charge 2 may not provide sleep stage information.

To optimize the accuracy of your Fitbit Charge 2's sleep tracking, it is recommended to wear the device snugly on your wrist, with the device positioned about 2-3 finger widths above your wrist bone. It is also best to simply wear the device to bed instead of using the "Begin Sleep Now" option in the Fitbit app.

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