Herbie Murray
Fitbit devices track sleep by monitoring movement and heart-rate patterns. When you haven't moved for about an hour, your Fitbit assumes you're asleep. It then tracks beat-to-beat changes in your heart rate, known as heart rate variability (HRV), which fluctuate as you transition between light sleep, deep sleep, and REM sleep. REM sleep, or rapid eye movement sleep, is associated with vivid dreams and plays an important role in mood regulation, learning, and memory. While some Fitbit users have questioned the accuracy of their REM sleep data, studies have been conducted using Fitbit sleep staging to analyse the timing of REM sleep and its relationship with total sleep time.
| Characteristics | Values |
|---|---|
| REM sleep | The stage associated with vivid dreams |
| REM sleep percentiles | Determined in relation to minutes after sleep onset and clock time |
| REM sleep and total sleep | REM sleep timing is more strongly associated with the timing of total sleep than with the timing of deep sleep |
| REM sleep and subjective sleep quality | A relationship exists between REM sleep consolidation and subjective sleep quality |
| REM sleep and heart rate | Fitbit tracks beat-to-beat changes in heart rate, known as heart rate variability (HRV), which fluctuate as one transitions between sleep stages |
| REM sleep and age | Older people produce less REM sleep |
| REM sleep and accuracy | REM sleep can only be properly measured through brain waves, but many people trust Fitbit for REM sleep tracking |
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What You'll Learn
REM sleep and heart rate
Sleep is divided into two main types: rapid-eye-movement (REM) sleep and non-REM sleep. During the non-REM stage, your heart rate, breathing, and blood pressure all decrease compared to when you are awake. However, during REM sleep, which accounts for about 20% of your time asleep, your heart rate and blood pressure can fluctuate.
Fitbit devices can estimate your sleep stages by tracking the beat-to-beat changes in your heart rate, known as heart rate variability (HRV). HRV is typically higher at night, indicating that sleep is a condition during which vagal activity is dominant. During non-REM sleep, the low- to high-frequency ratio (LF/HF) decreases significantly, indicating higher vagal influence on heart rate control.
Transitioning to REM sleep causes a decrease in vagal contribution to heart rate control, resulting in a relative prevalence of low-frequency variability of the heart rate. This can be interpreted as a condition of sympathetic dominance in the autonomic balance during REM sleep. Studies have shown that heart rate surges during REM sleep, with increases in heart rate ranging from 26.4% in cats to 35% in humans and canines.
The strong association between REM sleep and sympathetic dominance has been observed by various researchers. Lovett and co-workers found a 1:1 coupling between the timing of REM onset and increases in the low- to high-frequency ratio. Somers and co-workers reported a marked increase in muscle sympathetic nerve burst frequency and amplitude during REM sleep in normal human volunteers. These findings suggest a relationship between REM sleep and increased sympathetic nervous system activity.
The understanding of autonomic activity during sleep stages is primarily based on data obtained from animal studies. However, in humans, autonomic control of cardiovascular function during sleep has been linked to the occurrence of sudden death. Specifically, myocardial infarction causes a loss of vagal activation during sleep, resulting in a condition of relative sympathetic dominance. This may provide insights into understanding sudden death during sleep, as well as the relationship between sleep, sleep disorders, and heart disease.
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REM sleep and brain waves
Sleep is not a uniform state but is composed of several stages that can be differentiated by brain wave activity patterns. These brain wave patterns can be visualised using an electroencephalogram (EEG). Sleep is generally divided into two phases: REM (rapid eye movement) sleep and non-REM (NREM) sleep.
During REM sleep, the eyes scurry rapidly under closed eyelids, and the brain waves are similar to those during wakefulness. Dreaming occurs during this stage, and the body is temporarily paralysed, except for the muscles that control breathing and circulation. This stage of sleep is also referred to as paradoxical sleep, due to the combination of high brain activity and lack of muscle tone. REM sleep is important for mood regulation, learning, and memory, as the brain processes and consolidates information from the day before, storing it in long-term memory. If deprived of REM sleep, an individual will spend more time in this stage when next undisturbed, seemingly to make up for the lost time.
Non-REM sleep, on the other hand, is further subdivided into three distinct stages, each with its own characteristic brain wave patterns. The first stage is transitional between wakefulness and sleep, marked by a decrease in respiration, heartbeat, muscle tension, and body temperature. This stage is associated with alpha and theta brain waves. The second and third stages are marked by slow-wave sleep, characterised by low-frequency, high-amplitude delta waves. During these stages, the heart rate and respiration slow significantly, and it is difficult to wake the sleeper. Increased alpha brain wave activity during these stages has been linked to feelings of tiredness upon waking.
The Fitbit device can be used to track sleep stages, estimating them based on movement and heart-rate patterns. It can detect the length of time when movements indicate sleep behaviour, such as rolling over, and tracks beat-to-beat changes in heart rate, known as heart rate variability (HRV). When synced in the morning, the device uses this data to estimate the sleep cycles from the previous night. The Fitbit app allows users to view a sleep timeline graph and compare their sleep stage estimates with averages of others in the same age range and sex.
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REM sleep and sleep quality
Sleep is an essential component of health, and its timing, duration, and quality are critical determinants of a person's overall health. Sleep quality is influenced by the timing and duration of sleep, which contribute to performance and emotional health.
REM sleep, or Rapid Eye Movement sleep, is a stage of sleep associated with vivid dreams. It typically occurs during the latter part of the sleep cycle, with periods of REM sleep lengthening as the night progresses. While you sleep, your Fitbit device tracks the beat-to-beat changes in your heart rate, known as heart rate variability (HRV), which fluctuate as you transition between light sleep, deep sleep, and REM sleep stages. The Fitbit estimates your sleep stages by using your movement and heart-rate patterns.
REM sleep plays a crucial role in mood regulation, learning, and memory consolidation. The brain processes and consolidates information from the previous day during REM sleep, storing it in your long-term memory. A stronger phase relationship between deep and REM sleep with total sleep duration is associated with greater consolidation of REM sleep. This suggests a relationship between REM sleep consolidation and subjective sleep quality.
However, it is important to note that sleep tracking technology, including Fitbit devices, may not always provide accurate measurements of REM sleep. While Fitbit estimates sleep stages based on movement and heart rate patterns, REM sleep is most accurately measured through brain waves. Factors such as sleeping position, with arms placed under the head, can also impact the device's ability to record heart rate accurately. Additionally, individual sleep patterns can vary, and external factors such as alarm clocks can affect sleep timing.
Fitbit provides a Sleep Score as a quick way to gauge your sleep quality, based on heart rate, time spent awake or restless, and sleep stages. The overall sleep score is a sum of individual scores in three components: sleep duration, sleep quality, and restoration. The restoration component includes estimated oxygen variation, where high variations may indicate disturbances in breathing during sleep. Fitbit Premium also offers guided programs, such as "Habits for Restful Sleep" and "Get More Sleep," to help users improve their sleep habits and achieve longer sleep durations.
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REM sleep and mood regulation
Sleep and emotion are intimately related, with sleep disturbances restricting daily well-being and social functioning. Both NREM and REM sleep serve to modulate emotional and motivational drives, making individuals more emotionally flexible during wakefulness.
REM sleep, in particular, is involved in nightly emotional processing. It helps process and consolidate emotional memory, with dream production facilitating the processing of distressing emotions. Brain imaging studies have demonstrated the activation of the limbic and paralimbic structures of the forebrain during REM sleep. This supports the emotional processes that help us regulate the emotional events we encounter during daily life.
REM sleep appears to be a marker of dysfunctional or inadequate emotion regulation during the day, indicating the need for further emotion processing and regulation during sleep. For example, intensification of phasic REM sleep may indicate a need for further emotion processing. A study found that participants with pre-sleep depressed moods showed a pattern of decreasing negative and increasing positive affect in dreams reported from successive REM periods.
The adaptive influence of REM sleep on the regulation of emotion appears to be reduced after REM sleep deprivation. Without enough healthy sleep, including REM sleep, negative emotional reactivity is enhanced, and positive reactions to positive events are decreased. However, total or partial sleep deprivation or selective REM sleep restriction in depressed individuals has shown temporary improvements in energy and mood, with a regression towards depression after subsequent sleep.
REM sleep appears to play a crucial role in mood regulation, with deprivation potentially leading to impaired emotional regulation during the day.
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REM sleep and sleep patterns
Sleep is an essential component of health, and its timing, duration, and quality are critical determinants of a person's overall health. Fitbit estimates sleep stages by using movement and heart-rate patterns. When you haven't moved for about an hour, your tracker or watch assumes you're asleep. While you sleep, your device tracks the beat-to-beat changes in your heart rate, known as heart rate variability (HRV), which fluctuate as you transition between light sleep, deep sleep, and REM sleep stages.
REM sleep, or rapid eye movement sleep, is the stage of sleep associated with vivid dreams. REM sleep periods are typically longer as the night goes on. During a sleep cycle, you commonly switch from light sleep to deep sleep, then back to light sleep, and into REM sleep, and then the cycle generally repeats, but sleep patterns vary naturally.
REM sleep has been shown to play an important role in mood regulation, learning, and memory. While you sleep, your brain processes and consolidates information from the previous day so that it can be stored in your long-term memory. The timing of REM sleep seems to be more strongly associated with the timing of total sleep than with the timing of deep sleep.
Fitbit's sleep feature can help you look for patterns and recognize when you need to get more rest. The sleep score is based on heart rate, the time spent awake or restless, and sleep stages. Sleep impacts nearly every aspect of health, from daily mood to appetite, physical activity, and chronic conditions.
It is important to note that sleep trackers can be inaccurate, and it is recommended to consult a doctor if you have any concerns about your sleep health. Additionally, while REM sleep is important, "normal" sleep varies widely between individuals, and does not necessarily indicate a disorder.
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Frequently asked questions
REM stands for rapid eye movement sleep, which is the stage of sleep associated with vivid dreams. REM sleep has been shown to play an important role in mood regulation, learning, and memory.
Fitbit estimates sleep stages by using your movement and heart-rate patterns. When you don't move for about an hour, your tracker or watch assumes you're asleep. Additional data such as the length of time when your movements indicate sleep behavior (like rolling over) help confirm your sleep status.
REM sleep is traditionally measured in a lab using an electroencephalogram to detect brain activity, along with other systems to monitor eye and muscle activity. As such, it is difficult to accurately measure REM sleep without tracking brain waves. However, Fitbit's sleep researchers and the National Sleep Foundation have developed methods to estimate sleep stages by tracking heart rate variability (HRV) and movement patterns.
