Can Actigraphy Identify and Assess Leg Movements During Sleep?

With so many wearable medical devices available to us these days, it seems like using one to identify and track leg movements during sleep might be useful.

Is it possible to now observe periodic limb movement disorder (PLMD) using wearable devices or sleep-tracking apps?

Actigraphy 101

If you’ve never heard of actigraphy, you may be surprised to learn it’s been around a long time! In fact, the earliest movement-based sleep-wake detection devices — another name for actigraphy — were first developed about 50 years ago and remain a reliable way to measure body movement.¹

Sleep specialists have long measured limb movements during sleep for a host of reasons. But in the sleep clinic environment, these movements are typically measured through electromyography (EMG): electrodes affixed to the muscles in the legs.

EMG isn’t particularly “wearable” to the degree that a 21st-century actigraph is, chiefly because it’s not wireless.

Today’s actigraphy, however, is wireless. Because it’s worn as a watch, it’s eminently wearable. It’s also evolved over the last few decades to become far more accurate in its readings.

What is PLMD and why is treating it important?

PLMD is a movement disorder of sleep that affects between 4 and 11 percent of the population.²

People with PLMD experience repetitive movements as they sleep, which include kicking, jerking, toe flexing, cramping, or twitching at a rate of every 5 to 90 seconds and up to an hour at a time.

PLMD can greatly disrupt sleep — for both the person who’s unaware they have the condition and any bed partners who might be kept awake by it — leading to excessive daytime sleepiness as an outcome.

One possible cause of PLMD: low blood iron. In this case, treatment may include iron supplements and lifestyle changes such as reduced caffeine or alcohol intake. In some cases, medications may be necessary to reduce PLMD, or at least make it easier to sleep through.²

Is actigraphy right for diagnosing PLMD?

The challenges of diagnosing PLMD are many, and a wearable device that could do this work more easily — and with more focus on the comfort of patients getting tested – would be of great benefit to sleep specialists.

However, the American Academy of Sleep Medicine published clinical practice guidelines in 2018 which suggest the technology isn’t quite there yet.

In their paper, “Use of Actigraphy for the Evaluation of Sleep Disorders and Circadian Rhythm Sleep-Wake Disorders: An American Academy of Sleep Medicine Clinical Practice Guideline,” the contributing scientists explicitly state that they strongly advise against using actigraphy in place of EMG for the diagnosis of PLMD in patients of all ages.³

More about the AASM review

The purpose of the inquiry was to commission experts to provide a summary of evidence showing the safe use of actigraphy in the treatment of different sleep disorders. They looked at benefits versus harms, patient values and preferences, and the resources available to support the recommendation of actigraphy in these applications.

Interestingly, actigraphy was conditionally recommended as potentially useful for evaluating patients with other sleep disorders, such as insomnia or circadian rhythm sleep disorders. But when it came to PLMD, the recommendation came as a solid “no.”

The task force had only a few small studies to review. From them, they found measures of periodic limb movements coming from wireless actigraphy highly inaccurate when compared to more reliable measures provided by EMG wires.

They determined that the potential for overestimating or underestimating periodic limb movements using actigraphy could lead to potentially unnecessary treatment or to missed cases of PLMD.

Today's no... tomorrow's yes? Maybe...

This isn’t to say that there won’t be a simple wearable device in the future that can do the job. Sleep researchers constantly seek better, more affordable ways to collect sleep data that takes into account patient comfort. But the current actigraphy technology needs more complex measuring capabilities to do this.

For instance, actigraphy, by design, only records movement. It cannot detect, during periods of non-movement, if the person using the device is asleep or awake. That makes it impossible to identify movements made only during sleep.

One Canadian proof-of-concept study in 2019 points to a potential new algorithm that might detect periodic limb movements with some accuracy from any actigraphy device, but more research is needed to validate these findings.⁴

What about apps that claim to measure limb movements during sleep?

Though actigraphy has been useful for several decades in other applications, this doesn’t mean it can be used with any accuracy through a smartphone app or popular wearable tracker right now, even if manufacturers make such claims.

If you’re concerned you have a movement disorder of sleep like PLMD, your best bet is to consult a sleep specialist.