Detecting Sleep-Wake Patterns with the Use of Actigraphy Monitoring

Small Monitors Record Movement to Infer Sleep and Wakefulness

Fitness trackers like FitBit, Up band, and Apple Watch use actigraphy to document sleep and wake patterns
Fitness trackers like FitBit, Up band, and Apple Watch use actigraphy to document sleep and wake patterns. John Fedele/Blend Images/Getty Images

There are many potential ways to evaluate sleep, and one of the least intrusive, actigraphy monitoring, can be used to assess sleep at home with a device called an actigraph. What is actigraphy? How do fitness trackers like the FitBit, Up band, Nike Fuel band, and Apple Watch use this technology to track your movements and behaviors? Can these devices accurately detect sleep-wake patterns? Discover the answer and how these data may be used to help you to sleep better.

What Is Actigraphy?

Actigraphy is the continuous measurement of activity or movement with the use of a small device called an actigraph. These medical devices are often used in research and may be used in clinical practice in the management of sleep disorders, especially circadian rhythm disorders and conditions that cause excessive daytime sleepiness (hypersomnia) or insomnia. Periods of movement suggest wakefulness while those of relative stillness would likely correspond to sleep or quiescence.

With the push of a button, it may also have the ability to mark events such as bedtimes or wake times. Though professional devices can cost close to $1000, modern fitness trackers are also able to track your patterns of activity and infer rough estimates of sleep timing for closer to $50 to $200.

What Does an Actigraph Look Like?

An actigraph is a small, wristwatch-sized device. It is lightweight and typically worn on a limb, such as at the wrist or ankle.

It may be incorporated into a watch. It may also be a clip-on device that can be applied to your clothing as an accessory. More and more, these devices are becoming integrated into other everyday items such as clothing or bedding.

How Do Actigraphy and Fitness Trackers Work?

An actigraph monitors movement and can be used to assess sleep-wake cycles, or circadian rhythms, over an extended period of time.

It uses something called an accelerometer to record motion. These are often integrated into smartphones and can also be separate devices. This information is then used to create a graph. Active times result in a peak (or bar) on the graph while quiet times, such as sleep, will be represented by a flat line.

Actigraphs may be worn for weeks or even months. Generally, medical actigraph devices can record data for 24 hours per day for about two weeks. Common models can take measurements up to 32 times per second. They are useful to help determine whether disruptions in the sleep-wake cycle exist, as may occur in many different sleep disorders. They are generally not accurate enough to detect specific sleep stages, but this may change as the technology improves.

Sleep is more than just the absence of movement, as someone could lie still and the device would be unable to detect a difference. Devices that can incorporate additional measurements may eventually be able to detect the measures needed to truly identify sleep.

Current devices are not reliable for these purposes and do not hold up well against gold standard measures of sleep, such as polysomnography, that relies on the measure of the electrical patterns of the brain with electroencephalography (EEG).

Which Sleep Disorders Can Be Assessed with Actigraphy?

There are many sleep disorders that may be better understood by completing actigraphy monitoring. These may include:

Your doctor may order 2 weeks of actigraphy use with documentation using a sleep log. Many patients also bring this information collected from fitness trackers to their doctor when they are having difficulty with their sleep. Frequent awakenings at night may suggest obstructive sleep apnea and steps may occur without consciousness in parasomnias like sleepwalking.

What Are the Limitations of Actigraphy?

Aside from providing information about whether you are active or inactive, there is not much more that the devices can record. Furthermore, it isn’t very smart, so if you leave your actigraph sitting on your dresser, it may seem like you are sleeping for as long as it sits there. The memory may be limited, so it is necessary to download the information at regular intervals. In addition, often the results must be correlated with a sleep diary. As noted, these devices currently cannot accurately detect sleep stages.

Formal sleep studies, called polysomnography, provide much more detailed assessments of your sleep, but the simplicity and availability of actigraphy may be an acceptable alternative in some situations. In some cases, it may be a good first step in learning about your sleep.

As the technology advances, these devices may become more useful in the diagnosis and management of sleep disorders and contribute to other measures of health and wellness.

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