If you have had COVID, the flu, or even a cold recently, you might have been surprised when your fitness tracker seemed to know you were sick. Offering up stats like heart rate and body temperature, it turns out wearables, whether worn on your wrist or your finger, are quite reliable monitors of health.
“I believe that most of the value of using wearables comes from having access to a 24/7 record of your biosignals and observing changes over the long term,” Dimitris Spathis, Ph.D., artificial intelligence research scientist at Nokia Bell Labs and visiting researcher at the University of Cambridge, England, tells Bicycling. “Until now, we used to measure these vital signs in an episodic manner once or twice a year when visiting a doctor (or never, for example, with sleep tracking). Now we can see and learn how our body reacts to and recovers from very specific events, such as giving a stressful presentation.”
Getting to know your typical metrics will allow you to recognize a deviation. “Wearables are very capable of understanding a magnitude of things, from tiny changes in heart rate that indicate atrial fibrillation, to long-term variations of movement in Parkinson’s patients,” says Spathis.
More From Bicycling
Using artificial intelligence (AI), Spathis and his colleagues have begun to study whether trackers could replicate the expensive and time-consuming medical testing most often conducted in doctor’s offices. For example, VO2 max is the “gold-standard measure of cardio-respiratory fitness,” Spathis explains, but it typically requires a standardized test using a treadmill or cycle ergometer, and is rarely used due to its cost and risks.
That can be a problem, because low VO2 max may be a stronger predictor of mortality than traditional clinical risk factors such as diabetes, hypertension, or smoking, Spathis says.
In 2016, the American Heart Association published a scientific statement recommending that cardiorespiratory fitness, quantifiable as VO2 max, be regularly assessed and used as a clinical vital sign. This is why Spathis and his colleagues studied whether tracker information correlated with more complicated lab testing. “We validated these VO2 max estimates using both maximal (reaching max heart rate) and submaximal tests,” he explains.
In other words, it seems likely—although certainly more testing needs to be done—that trackers may help predict health outcomes. Not only that, when users get immediate feedback from their wearables, they can, if they choose, positively affect those outcomes.
“Having objective data available is very helpful in establishing good [health] habits,” Kim Geist, M.S., a Macungie, Pennsylvania-based, level 2 USA Cycling-certified coach tells Bicycling. “Those good habits can lead toward meeting goals. A tracker can provide feedback on how everyday choices affect certain outcomes, as well as serve as a constant reminder to aim to make good choices.”
Right now, according to researchers, wearables are not reliable when it comes to calories, whether you’re tracking your input (through eating) or the calories you burn through exercise and daily movement.
It’s true that wearables, at best, only give estimates in most categories, but much of the data is still considered reliable enough for users to better understand their own health. That’s why it’s smart to pay attention to sleep, heart rate, heart rate variability (or the time between your heart beats, which should be consistent, but may change due to stress or illness), VO2 max, and a variety of other fitness metrics to help with recovery, goal-setting, and safety.
Here, how to tune into those metrics on your fitness tracker, so you can use them to hack your health:
Hack Your Sleep
By wearing your tracker to bed and connecting your sleep scores with your before-bed habits
We are often told to “get seven to nine hours of sleep each night” which implies a full night of uninterrupted sleep, but even a good night’s rest may include getting up to go to the bathroom. A tracker with sleep readings can help you determine your individual sleep pattern and maximize your time in bed.
Wear your tracker for 14 nights in one month and Fitbit Premium will offer information on your personal sleep pattern, alerting you to how much REM sleep—important for brain health—you’re getting on average and if you’re in bed for a long time before falling asleep, which could clue you in to better nighttime habits. It also reveals how much time your heart rate fell above and below resting and your restlessness, all signaling the restoration of your sleep.
Similarly, after a few nights of wearing Oura Ring, it will set an ideal bedtime for you—following a specific sleep schedule is super important for setting your circadian rhythm up for success. It will then remind you when it’s time to wind down. In the morning, it offers insight into different sleep stages, how long it took you to fall asleep, and the efficiency of your sleep, based on the time you spent asleep versus awake in bed.
Sleep is a common struggle for cyclists, so Geist says you could use your tracker to try a variety of variables for a few nights, such as changing the room temperature, putting away your phone earlier to reduce blue light exposure, drinking less alcohol, and trying to wake up earlier with an alarm clock. In the morning, when the tracker gives feedback on sleep quality, check how the change you made affected that feedback. (Just make sure to try it for a few nights or weeks to get a full picture.)
Hack Your Peace of Mind
By looking at your heart rate variability and actively addressing stress
“Another useful biomarker users can check more frequently is HRV or heart rate variability,” says Spathis. “HRV is a good measure of recovery and is considered one of the best metrics for determining the body’s readiness to perform.”
Wearables, such as Oura Ring and Garmin, use HRV as part of its daily readiness scores. Fluctuations in HRV are undetectable except with specialized devices. With these wearables, a user may be alerted that their heart rate is responding to stress (as shown by low HRV) even before they become conscious of the stress. A low HRV might also alert you, via your tracker, to take more rest time or go easier on a workout for the day.
If you consistently see your HRV numbers going down, it’s probably time to take a look at your stress levels and workout intensity, and see if there’s a place for more down time.
Again, it’s up to the user to connect the tracker information to their habits and make adjustments, including maybe tuning into some of the app’s connected breathwork or meditations in order to see if these practices can affect heart rate so that it is more stable even during times of stress. Fitbit, Apple, Garmin, Polar, and Oura all have connected meditations to help users lower their stress levels without needing to take a class or even leave their seats.
Hack Your Fitness Goal-Setting
By looking at how much you move throughout the day (not just in your workouts), and paying attention to heart rate
Of course, most wearable users are eager to get their steps in or track another fitness category, such as cycling miles and pace. While every athlete will have their own personal goals, just wearing a tracker has been shown to increase movement and activity for users.
According to Australian researchers who reviewed nearly 400 studies involving 164,000 people, fitness trackers, pedometers, and smart watches motivate users to exercise more. They found that users with wearables walk up to 40 minutes more each day and also do six minutes more moderate-to-vigorous physical activity every day than those who don’t wear them. So, if your basic goal is to “just do more,” a fitness tracker, such as the Polar Ignite 3 and the Apple Watch (which motivates you to close those rings), can help you build both steps and intense exercise into your days.
Another suggestion is to keep track of your heart rate recovery (HRR), which is both a measure of fitness, as well as measure of heart health overall. According to a 2018 study published in the Journal of the American Heart Association, in which researchers analyzed data from at more than 40,000 participants, rates of HRR immediately after you stop exercising could predict overall health and likelihood of death.
Many wearables and trackers include heart rate recovery tests, but it’s also something a user can do on their own using the step method. The Oura Ring suggests doing the test with a rowing machine to get up to a max effort.
All of the trackers, including Garmin, Polar, Fitbit, and Apple track heart rate, but it’s important to know that none of these are medical grade devices, as discussed earlier, so if your heart rate recovery time worries you, chat with your doctor about it.
The key to improving heart rate recovery is more aerobic exercise, according to a 2014 study of 10 track cyclists and 15 road cyclists. The research found that while a faster recovery rate indicates optimal fitness and absence of overtraining. In other words, if you regularly keep track of your recovery rates after hard rides, and you notice a sudden change, consider a rest day.
Hack Your Recovery
By checking your scores on readiness for exercise
Speaking of rest, almost all wearables and tracker models have some sort of daily readiness or morning monitor to help a user determine how hard they should push their workout on any given day.
The Oura Readiness score pulls together an evaluation of more than 20 different body signals, such as sleep, activity, heart rate variability (HRV), and body temperature to give the user feedback before the day begins. Garmin offers a Morning Report as well as Body Battery Energy Monitoring to make workout intensity suggestions for the day. Fitbit and Polar wearables have similar features.
Should you listen to your wearable in planning your workouts and recovery times? Yes and no, says Geist. The goal shouldn’t be to rely on the tracker forever, but to use its feedback to help you tune into your body. It should help you learn how your body responds and “what it feels like to be responding well or overreaching.”
Just as you get to know your tracker and its features, notice if its features seem to match how you feel and whether its recommendation, such as reminding you to take a recovery day, actually matches your own instinct about when to rest.
Hack Your Survival
By using fall detection and heart health measures
Finally, even if you are low-tech and head out the door with nary more than a bottle of water, you should know that wearables are also helpful in acute health emergencies, and can support those with chronic health issues.
An Apple Watch will alert emergency services if it detects a hard fall. Garmin has automatic incident detection and manually triggered assistance alerts, both of which send a message with the users’ real-time location to emergency contacts. These systems, like all technology, are known to be glitchy; lots of people have stories of crash alerts that turned out to be false. But it’s also true that many people credit their devices with providing life-saving information to emergency services.
In addition to accidents, Apple has also put key heart health indicators in its Watch. You can set it up so you get alerts when your heart rate is too high, or to have it check for irregular rhythms that might signal atrial fibrillation. It also takes ECG readings via the specific Watch app, so you get a better understanding of your heart rhythms.
While not crash or emergency-specific, in October 2022, the American Heart Association released a study, which found that people who most need wearable health devices are the least likely to wear them. According to the study, “only 12% of people with cardiovascular disease older than 65 years of age used wearable devices, even though it is estimated that half of all people with cardiovascular disease are older than age 65.”
For decades, many people joked about wishing they could have a trainer who would help them make good health and fitness choices in their pocket. Today, that trainer is here. She just looks like a watch.
Donna Raskin has had a long career as a health and fitness writer and editor of books and magazine articles. She bikes in a nearby county park, lifts weights, takes Zumba, and loves to walk/run with her dog, Dolly.
