Buzz
This article is part of Find Your Fit Tech, Mytour's guide to choosing fitness wearables. I explore whether these devices truly enhance health, how to pick the best one for your needs, and how to maximize the insights they provide.
Wearing a fitness tracker gives you access to a treasure trove of personal health metrics. Rather than simply feeling tired, you now have a sleep score, step count, and even a virtual trainer suggesting workout adjustments based on your fatigue levels.
Brands are competing to impress with an overwhelming amount of data, but when you sift through it all, you’ll realize a key insight: only a portion of that information is truly valuable.
Why You Shouldn’t Fully Rely on Your Wearable’s Data
Wearables present a paradox: there’s often a gap between what you hope to achieve and what a wrist-bound device can actually deliver. You might aim for better sleep, faster runs, weight loss, or staying active, while your device offers metrics like heart rate, skin temperature, and distance covered. These two sets of goals and data don’t always align seamlessly.
To better understand wearables, it’s useful to distinguish between what they measure and what they estimate. I prefer using Marco Altini’s framework, which organizes these into three distinct categories:
Measurements, which are direct or minimally interpreted data from sensors. Examples include heart rate, skin temperature, and movement.
Calculations or estimates of measurable metrics. For instance, wearables might estimate time spent in different sleep stages, which could theoretically be compared to a sleep study. However, studies validating these features have shown mixed results.
Calculations or estimates of unverifiable metrics. Many advanced-sounding features fall here. If your app assigns a “sleep score” of 66, there’s no way to verify its accuracy—it’s essentially a fabricated metric.
This leaves us with two key questions. First, is a specific metric accurate? Accuracy can only be assessed for the first two categories, and only when supported by large-scale, tested data.
Second, is the metric useful? This depends entirely on context. What real-world changes do you make based on your fitness tracker’s data? For instance, if it leads to more sleep or exercise, that’s likely beneficial. However, it’s easy to obsess over arbitrary metrics that don’t truly help. Skipping workouts for a better recovery score or pacing your living room at 10 p.m. to hit 10,000 steps might not actually improve your fitness.
Accuracy is just one piece of the puzzle
Thankfully, researchers can compare wearable data to established measurement standards. They evaluate how well devices track heart rate, sleep stages, or calories burned during exercise.
Unfortunately, these studies often occur after devices are released, typically in limited numbers and with insufficient funding. By the time results are published, companies have already moved on to newer models. I explored some of these findings in this article on calorie burn (spoiler: most devices struggle with accurate calorie calculations).
When studies are conducted before a device launches, they’re usually funded or performed by the company selling it. These studies can only validate direct measurements or estimates of measurable data (like sleep stages). By definition, there’s no way to verify the accuracy of fabricated metrics.
With all this in mind, let’s explore the types of data your fitness tracker provides and which metrics are truly worth focusing on.
Focus on total sleep time (but ignore sleep stages)
Sleep tracking devices have seemingly become more advanced over time, but their core functionality remains largely unchanged.
The most valuable feature of a sleep tracker is its ability to give you an honest picture of how much sleep you’re actually getting. When you’re asleep, your movement stops, and metrics like heart rate and skin temperature help the device distinguish between real sleep and activities like reading in bed. (Some devices perform this task better than others.)
However, wearables cannot accurately differentiate between sleep stages. Proper sleep stage analysis requires brain wave monitoring, which a wrist-based device simply can’t achieve. (This is why I found it amusing, yet not concerning, when I wore both an Oura and a Whoop simultaneously and received conflicting advice. The Oura claimed I wasn’t getting enough REM sleep, while the Whoop suggested I was getting too much.)
Some devices have become remarkably adept at estimating sleep stages, but these remain educated guesses. For instance, the Oura ring—often praised as one of the top devices—reports that its latest algorithm is 92% to 93% accurate in detecting sleep versus wakefulness, but this drops to 76-78% accuracy for identifying sleep stages. The study data reveals that the algorithm tends to overestimate for some users and underestimate for others, with accuracy also varying by the wearer’s age. While this is a technological marvel, it’s not reliable enough to base personal decisions on.
Even if sleep stage data were perfectly accurate, I still wouldn’t prioritize it. The advice for improving deep sleep, light sleep, or REM sleep always circles back to one thing: get more sleep. Whoop suggests that to increase deep sleep, you simply need more time in bed, directing users to Sleep Foundation tips on general sleep hygiene—the same guidance they offer for boosting REM sleep. The pattern is clear.
Here’s the takeaway:
Trust the total sleep time reported (but cross-check it with your own experience—does it seem realistic?)
Ignore sleep stage breakdowns or sleep quality scores.
Rely on your heart rate data during workouts (but take heart rate zones with a grain of salt unless you’ve done your own research)
Heart rate is a straightforward metric: your heart is either beating at a given moment or between beats. This simplicity makes it reasonable to expect a relatively accurate measurement.
In reality, accuracy varies by device, but most leading brands perform well enough for everyday use. For instance, a 2020 study found that the Apple Watch Series 4, Fitbit Charge 2, Garmin Vivosport 3, and Xiaomi Mi Band 3 all delivered reliable heart rate readings during rest or steady exercise.
Trackers often struggle with accuracy during high-intensity movements. If your heart rate fluctuates rapidly during vigorous activity, a wrist-based device might miss some spikes. However, for assessing overall workout intensity—like ensuring you stayed in zone 2 during a jog—the sensor is generally sufficient. For precise heart rate data, a chest strap is a better choice.
But what about heart rate zones? This is where complexity arises. If you train using heart rate, you’re likely familiar with zones. Zone 1 represents minimal effort, while zone 5 is a maximum effort lasting only seconds. Workouts often target specific zones, like an easy jog in zone 2. However, two key issues complicate this:
“Zone 2” lacks a universal definition; each company defines its zones differently.
Zones rely on assumptions about your heart, typically estimating maximum heart rate based on age, which is often inaccurate.
If you’ve ever completed an “easy” jog only to find your tracker claims you were in zone 5 the entire time, your zones were likely miscalibrated. This usually happens because your wearable uses a formula to estimate your max heart rate and bases zones on that guess.
However, all heart rate prediction formulas are flawed, and their accuracy declines with age. The common method of subtracting your age from 220 has little to do with your actual maximum heart rate. Researchers in the linked study recommend using graded treadmill tests to determine max heart rate instead of relying on formulas. Similarly, the American Council on Exercise advises trainers to disregard formulas entirely, suggesting they either use exercise tests for personalized zones or rely on RPE (how hard you perceive your effort) to design workouts.
If estimating effort on a scale of 1 to 10 seems imprecise, it’s still more reliable than depending on zones derived from flawed formulas. Neither method is perfect, but perception beats guesswork.
Here’s the summary:
Trust your heart rate data for overall exercise intensity (focus on the big picture, not momentary spikes)
Ignore heart rate zones if they’re based on default settings.
Rely on recovery metrics like HRV (but skip readiness scores)
Do you need to monitor your recovery? Not really. Most people can stop right there. However, some of us enjoy seeing how exercise and sleep interact and understanding our body’s response to illness or stress. I’ll admit this data isn’t essential, yet I’m personally attached to my Oura ring. I simply enjoy reviewing the numbers.
When it comes to recovery, there’s a significant difference between what heart rate metrics reveal and what an app determines as your “recovery” or “readiness.”
Resting heart rate often rises during stress or illness. It can jump after alcohol consumption or poor sleep but decreases over time as your cardiovascular fitness improves.
Heart rate variability (HRV) tracks the variation in your heartbeats. Higher variability is a positive sign, typically indicating good health, low stress, and quality sleep.
Readiness or recovery scores, such as Body Battery, combine RHR and HRV with other data to produce a single number reflecting your overall state. These scores don’t just measure your body’s response to exercise and sleep—they also factor in workout intensity, sleep quality, and other variables.
Because recovery scores incorporate so many elements, they often stray from what you’re actually trying to assess. For instance, light cardio on my rest days helps me recover from intense workouts, but Oura’s algorithm views this as excessive activity and lowers my score. It also fails to account for times when I intentionally push myself to build endurance.
Reviewing my data, I’ve noticed no meaningful link between days I excelled in the gym or competitions and days Oura deemed me well-recovered.
I’ve previously discussed a smarter way to use readiness data. Forget the scores and interpret the measurements within context.
Here’s the takeaway:
Trust metrics like HRV and resting heart rate
Ignore scores such as recovery, readiness, or body battery that attempt to condense too much into a single number.
Rely on calorie burn estimates, but only for general trends
For many, the standout feature of wearables is their ability to estimate daily calorie burn. No more guessing how much to eat—just glance at your wrist for the number!
Unfortunately, they fall short of delivering on this promise. As I’ve mentioned, fitness trackers are notoriously unreliable at calculating calorie burn. While they’re better than those misleading elliptical machines, they often underestimate for some people and activities while overestimating for others. There’s no way to know if the number is too high, too low, or just right—so what’s the point?
I find calorie burn data helpful for broad trends. If your daily burn increases from 1,800 to 2,200 calories due to marathon training, it’s a clear sign to eat more to fuel your runs.
However, I wouldn’t obsess over specific numbers. For example, burning 100 fewer calories today than yesterday doesn’t mean you should skimp on salad dressing. Similarly, if your watch claims you burned 600 calories ice skating once this year, that doesn’t justify an extra 600-calorie dessert. Your device isn’t precise enough for such calculations.
Here’s the summary:
Trust the overall trend to gauge whether your activity levels have increased or decreased
Ignore the precise numbers, particularly for single workouts. Prioritize fueling your body and feeling good over matching exact figures.
Rely on your step count, but maintain perspective
Personally, I have mixed feelings about step counts. When I’m walking or running frequently, I enjoy watching my step count rise. However, during periods when my workouts focus on cycling or gym sessions, my step count plummets, even though I’m still active.
In the end, your daily step count isn’t a critical metric, but it’s an easy one to track. Even without a smartwatch, your phone likely counts steps (check your Apple Health or Google Fit app).
If step counts motivate you, go ahead and track them. Just ensure you’re honest about whether they’re positively impacting your life.
If you’re wondering about accuracy: different devices will never agree on your daily step count. Some will undercount, others will overcount, and each will track certain activities better than others. Don’t stress over these discrepancies. Instead, focus on comparing daily readings from the same device.
Here’s the summary:
Trust your step count (it’s not perfectly accurate, but it doesn’t need to be).
Ignore the idea that hitting a specific step goal daily defines your health or worth. Use step counts if they help you, and disregard them if they don’t.
Rely on your cardio fitness or VO2max estimate, but treat it as a general guideline
Most devices now provide a VO2max estimate, often labeled as a “cardio fitness” score.
VO2max is a lab-measured metric (often used by professional athletes) that quantifies how much oxygen your body can utilize at once. In simple terms: higher VO2max indicates better cardiovascular fitness. Individuals with high VO2max can typically run longer and faster than those with lower scores.
Research shows that VO2max is linked to better health and longevity, but this isn’t because VO2max directly improves health. It’s simply one of the easier metrics to measure within aerobic and athletic performance. (Other cardiovascular fitness metrics also correlate with longevity.)
Wearables assess cardio fitness differently than lab-based VO2max tests. Instead of using exercise equipment and oxygen masks, they track your heart rate during runs or walks. If you can run faster at the same heart rate or maintain the same speed with a lower heart rate, your cardio fitness has improved.
Should you compare this number to VO2max charts? No, because it’s not an exact VO2max measurement. However, you can monitor this number over time and trust that your fitness is improving when it increases. Just remember to understand how your device calculates it and consider the context. Some watches’ readings can be skewed by hot weather, and if you rarely walk or run outdoors, the device won’t have consistent data to base its calculations on.
Here’s the summary:
Trust the trend of this metric over time (an increase indicates improvement)
Ignore the exact number, and don’t rely on it heavily if you don’t regularly run or walk outdoors.
Rely on your mileage and GPS data, most of the time
When engaging in outdoor activities like running or cycling, your watch will track the distance covered. This is useful for monitoring overall mileage and speed—but there are limitations.
First, GPS isn’t always precise, especially in urban areas where signals can reflect off buildings. For the most accurate location data, opt for a device that supports multiple satellite systems (like GLONASS and Galileo alongside GPS) and, if possible, dual-band GPS. We cover this in more detail in our guides for running watches and outdoor adventure watches.
That said, modern running watches and smartwatches offer far better location accuracy compared to devices from five or even 10 years ago. Your watch is likely to be significantly more accurate than your phone.
However, it’s not flawless. Occasional glitches can be frustrating. For instance, in a local park where two roads run parallel, my watch sometimes mistakes one for the other. When it corrects itself, the GPS track suddenly shifts to my actual location, making it seem like I teleported and ruining my split time for that mile.
So don’t stress if your watch records a distance slightly different from what you expected. And don’t worry if your smartwatch shows 5.3 kilometers for a 5K race. Your watch measures distance differently than a race course’s certifying body, so it’s normal for it to show a slightly longer distance. Your official finish time is what matters for your personal record.
Here’s the summary:
Trust the distance and location data, but take it with a small margin of error.
Ignore the idea that race distances or locations will be pinpoint accurate. While modern watches are more precise than older models or phones, perfection isn’t achievable.
Whether you trust badges and streaks is a personal choice
This brings me back to the earlier point: the gap between what a wearable can measure and its actual impact on your life.
Wearable brands attempt to bridge this gap through gamification. You can earn badges and maintain streaks as long as you keep engaging with the device and its app. If these small rewards keep you using the device, and using it improves your health, it’s arguably beneficial.
However, it’s not always straightforward. On one hand, regular use of an activity tracker often encourages more exercise and may aid in weight loss. On the other hand, the tactics used to promote consistency can sometimes backfire. If your only motivation is maintaining a streak, once that streak breaks, you’ll need another source of motivation. Streaks can act as training wheels, but they can’t replace the process of building a lasting habit.
Here’s the summary:
Trust that taking action will help you find your own motivation. (If you try, you’ll likely succeed!)
Ignore the idea that badges and streaks alone will sustain your progress.
