Black Friday and Cyber Monday may be behind us, but there’s still plenty of time for holiday shopping. Wearables for sleep-tracking are always a good gift choice, but you may be wondering which devices are good enough for fatigue risk management systems (FRMS) in the real world. Last year, Philips Respironics chose to retire the Actiwatch series. Actiwatches were the research actigraph brand used to measure sleep in the field for innumerable hospitals, laboratories, airlines, clinics, military personnel, etc. If your organization relied on Actiwatch 2.0s, Pros, or Spectrum Plus devices for sleep data collection, those Cyber Monday deals on smartwatches may have looked awfully tempting. You aren’t alone. According to Google’s Holiday 100—an annual list of 100 gift ideas and insights based on trending searches throughout the year—“smartwatch” searches have spiked every December since 2012 [1, 2].
One of the most frustrating issues with commercial sleep trackers is their questionable accuracy. “Accuracy” is a tricky term when it comes to sleep tracking. The term is used in everyday language as a catch-all phrase for something being correct. In technical terms, however, accuracy refers to the proportion of true positive results (both true positive and true negative) over all possible results and is just one measure that scientists use to determine a device’s validity—meaning that it actually measures what it says it does. Sensitivity and specificity are the two other metrics used to gauge the validity of sleep trackers. In sleep tracking, sensitivity refers to the number of times a device says that a person is sleeping when they are actually sleeping. For example, if you fall asleep in front of a Hallmark movie and your watch picks it up, that’s sensitivity. Specificity is the number of times that a device says a person is awake when they actually are awake. So, if you wake up in the middle of the night because you hear reindeer hooves on your roof, and your tracker picks it up, that’s specificity. Accuracy is sensitivity plus specificity.
Sleep trackers can establish their validity through a process called evaluation testing. Evaluation testing starts in the laboratory by comparing a sleep tracker against polysomnography (PSG). The next step is to evaluate the tracker in the field against an actigraph or sleep diary. Evaluation testing establishes how similar to PSG a tracker’s measurement of sleep duration and other metrics are. Measurements are never perfectly in sync, but a few minutes difference between sleep estimates never hurt anyone, right? This tenuous assumption lies near the heart of the debate about whether commercial sleep trackers are viable replacements for traditional actigraphs. Fortunately, a group of researchers from the Department of Defense Biotechnology High Performance Computing Software Applications Institute (BHSAI) and the Henry M. Jackson Foundation for the Advancement of Military Medicine just published a multi-study comparison of laboratory-validated sleep trackers against the Unified Model of Performance (UMP) [3, 4] —a biomathematical model that, like the SAFTE model, is based on Borbély’s two-process model of sleep regulation [5]. Fun fact: when models use objective sleep data to predict fatigue, most models produce relatively similar results [6] (read the full article here).
The new publication, helpfully entitled " Can we rely on wearable sleep-tracker devices for fatigue management?” was published in the journal SLEEP this past November. The authors compared sleep measurements from 18 unique sleep trackers that had been tested against PSG and alertness predictions made by the UMP for simulated sleep schedules using either PSG estimates or the sleep tracker estimates. Nine devices resulted in agreement rates greater than 80%, indicating that they could be used to measure sleep duration for FRMS without sacrificing accuracy. If you’re looking for a gift item, the devices that passed muster were Fitbit Flex, Fitbit Charge 2, Fitbit Alta HR, the Oura ring, Withings Pulse O2, Basis Health Tracker, SenseWear Pro Armband, Fatigue Science Readiband, and IBR’s own Zulu watch.
Another reason smartwatches may be on fatigue managers’ shopping lists this year is that they have the potential to track some desirable non-sleep-related contributors to fatigue—stress, workload, and even illness. Unlike traditional actigraphs, almost all sleep-tracking smartwatches incorporate heart rate tracking nowadays. Heart rate variability (HRV) shows some hope as a physiological measure of both physical and mental workload [7, 8] as well as a measurement of stress. If wearables can track workload and stress, then they offer feedback solutions to improve both symptoms of sleep deprivation and burnout [9, 10]. Workload and stress have become important buzzwords to the fatigue risk management community in these post-pandemic years.
Rebound travel following the pandemic is high, but there is still an ongoing staffing shortage in the transportation industry [11-13}. Intent to travel between Thanksgiving and mid-January is up across all age and income groups, according to findings from the 2023 Deloitte holiday survey [14] (full survey here). Deloitte also conducted a survey on work attitudes from millennials and Gen Z (who comprise the majority of the workforce now) and found that roughly half of young workers feel stressed and burned out all the time [15] (download the full report here). With an influx of travel and shipping occurring on the heels of the COVID-19 pandemic and the Great Resignation, it’s no wonder that pilots, drivers, and crew members are feeling the crunch. Accounting for psychological fatigue is much less well understood than accounting for the physiological impact of sleep debt, jet lag, or long days, so if a smartwatch promises to track something even close to workload, fatigue risk managers are bound to be interested.
The good news is that the 2023 SLEEP publication takes sleep trackers a step closer to scientific legitimacy for FRMS, but the bad news is that HRV for the estimation of workload and stress management is still in its infancy. This is not to say that we will never have a viable measure of psychological fatigue; it just means that wearables aren’t the answer to managing symptoms of burnout for your workforce right now. Organizational support—the sense that one’s company cares about them—might be a better safeguard against burnout at the moment. It is possible that the gift of a smartwatch for personalized fatigue risk management would convince employees that their company cares about their well-being. Looking at the Deloitte generational survey results, though, we must note that millennials and Gen Z are especially stressed about the cost of living and the economy. Taken in tandem with Statistica’s 2023 ranking of most popular gift items (see chart below or original post here), a year-end bonus might be the best way to lower stress levels this holiday season. Workers are likely to sleep better too, knowing they can afford their rent in 2024.
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