Ever since the first FitBit was released back in 2009, activity trackers have steadily been making their way into the mainstream—today, brands like Whoop, Garmin, and Apple are competing for real estate on our extremities in an industry worth over $13 billion.
As these devices have evolved to serve up increasingly diverse data about our bodies, however, they’ve inadvertently made it more challenging to discern which metrics are actually worth our attention. As Sam Setareh, MD, MS, director of clinical cardiology at Beverly Hills Cardiovascular, puts it, “It’s an information overload.”
Regardless, activity trackers have the potential to be useful in helping us to quantify our health, fitness, and wellness, and providing the insights we need to make informed adjustments to get us closer to our goals. To cut through the noise and help you focus on the most useful information being tracked by your devices, GQ asked experts from the fields of medicine, sports performance, nutrition, science, and data to weigh in. Here are the five metrics that are most worthy of your time and attention.
Heart Rate Variability (HRV)
“I firmly believe that HRV is the most important metric that we can be tracking when it comes to any type of wearable device,” says Justin Roethlingshoefer, MS, performance coach and founder of health coaching business Own It.
It’s different from resting heart rate or maximum heart rate—HRV measures the minute fluctuations in time
between heartbeats. A powerful indicator of holistic health, HRV is influenced by a vast spectrum of factors, ranging from daily stress and workout strain to heart problems and mental health conditions like anxiety and depression. “I don't know that there's really any other marker that gives you a better understanding of how you're doing both psychologically and physiologically,” says Kristen Holmes, global head of human performance and principal scientist at Whoop.
In its most useful form, HRV is a kind of master status indicator for your body. It can reinforce that your lifestyle is working for you, or that something under the hood needs adjusting. “It makes you take an honest look at your lifestyle. What does your sleep look like? What do your daily stressors look like? What does your training look like?” says Chris Mohr, PhD, RD, co-founder of well-being coaching service Mohr Results.
Measured in milliseconds, a normal HRV for adults can range from below 20 to above 200, depending age, gender, and other factors. Experts we spoke with recommend paying attention to your personal trend, rather than an absolute number—a relatively high HRV means you're ready to push, while a HRV decline indicates it's time for rest and recovery.
V02 Max
V02 max is generally regarded as the ultimate measure of aerobic fitness. Essentially, it is an indicator of your body’s ability to consume oxygen during physical exertion.
For the most accurate measure of your V02 max, you’ll have to schedule a lab session. Luckily, for the vast majority of us, that won’t be necessary, because many activity trackers actually provide a pretty good estimate of your V02 max based on other inputs. While any V02 max reading calculated outside of a lab will only be an estimate, that’s more than enough to track your progress over time. “With any of these metrics, the trend is the most important, rather than the isolated individual data points,” says Dr. Setareh.
Sleep Consistency
It should be no surprise to see a sleep metric on this list, as sleep is universally considered to be one of the most important things you can do for your health. Most activity trackers capture a variety of sleep data, and they tend to highlight things like sleep duration, disturbances, and the amount of time you spend in various phases. While these are interesting numbers to browse, they are downstream from a single metric that ultimately dictates the quality and restorative potential of your sleep.
“Sleep consistency is at the very tippy top in terms of metrics that you want to pay attention to,” says Holmes. Unlike sleep duration (the total time you spend asleep) or sleep quality (the time you spend in REM and slow-wave sleep, as a percentage of sleep duration), sleep consistency tracks how consistently you’re going to sleep and waking up at the same time each day, which a 2024 research paper in the journal
Sleep correlated with a number of benefits, including lower risk of dying from heart problems, metabolic diseases, cancer, and other causes.
Steps
“It's not the sexiest answer, but daily step count is a good one to keep your eye on,” says Dr. Mohr. “It seems like we're coming back to the benefits of general physical activity. I think for a while we got away from the importance of that and got into very specific fitness information and forgot about how just basic moving around is really great for your health.” Recent research found that walking up to 8,800 steps per day reduced the risk of mortality and cardiovascular disease by 60% and 51%, respectively.
“There's so much statistical power in there that it's almost like you can't argue against it,” says Milica McDowell, DPT, CEP, vice president of operations at Gait Happens. “If I asked you to do an activity that's going to reduce your risk of getting a disease by half, would you do it? Some of the other data that we get from these activity trackers is a little more subjective, but this is a quantifiable number.”
Respiratory Rate
Your respiratory rate is the number of breaths you take per minute. While it’s a relatively simple metric that you could measure even without a fitness tracker, this is another one where the trend is more useful than a specific number, says Dr. Setareh.
A noticeable and sustained increase in respiratory rate could be an indicator of anything from an allergic reaction to anxiety, but more often than not it means you’re about to get sick.
“One of the biggest culprits of an increase in respiratory rate is going to be a lower respiratory tract infection, which of course is also what COVID is,” says Holmes. “So I think it’s, especially in this day and age, absolutely a metric that you want to pay attention to.” —
Dean Stattmann
