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Why you might want to take fitness tracker accuracy with a grain of salt

Your fitness watch probably isn't giving you 100% accurate numbers, and that's okay.

Published onFebruary 14, 2022

The Samsung Galaxy Watch 4 on a wrist showing body composition analysis.
Jimmy Westenberg / Android Authority

Fitness devices are getting more and more powerful every year. Companies such as Garmin, Fitbit, Samsung, and others are always adding new features to their devices that keep track of everything from simple step counts to potentially detecting sleep apnea. It’s actually crazy how much these little computers can keep track of throughout the day.

But should you trust your wearable to report all those numbers accurately? Maybe not all the time. And that’s okay.

“What metrics should be taken with a grain of salt?”

fitbit premium review get more sleep metrics guided program 2

I hate to say this, but that step count on your fitness tracker probably isn’t accurate. It may be accurate within a few hundred steps, but it’s definitely not right on the money.

Most people wear their fitness trackers strapped to their wrists. Wrist-based devices need to do a lot of guesstimating in order to count steps. Most fitness trackers do this by utilizing something called a three-axis accelerometer — a little module that senses (you guessed it) acceleration. Gyroscopes, too, help fitness trackers keep track of orientation, and altimeters help your wearable track altitude.

Accelerometers, gyroscopes, and altimeters might be the best tools for wearables to sense your steps, but they’re always going to be off. Why? Because we’re all human and we all move around throughout the day in ways that aren’t traditional steps. The trackers sense and record those movements and potentially think you’re taking steps. I just moved my hands around in the air and my Garmin running watch counted 12 steps, for example.

Plus, different trackers are using different algorithms to keep track of all this data, so no two wearables will report the same numbers.

See also: Fitbit vs Garmin — Which ecosystem is right for you?

Most wearables nowadays also come with optical heart rate sensors. Some devices record all-day heart rate, some record every few minutes, and some only record when you manually hit a button or start a workout. Resting and active heart rate, heart rate zones, and other nitty-gritty heart rate details are also inaccurate most of the time.

HUAWEI Watch GT 3 heart rate zones closeup
Kris Carlon / Android Authority

Optical heart rate sensors work by shining an LED directly onto your skin and monitoring how that light reflects off your blood vessels. Sensors in your fitness tracker then pick up all that information and process it into easy-to-understand pulse readings.

However, there are a number of factors that can skew this data. The color of your skin, how much hair you have on your wrist, and how tightly you’re wearing your tracker can all affect those resting and active heart rate numbers. Even the modules themselves aren’t all created equally. Different fitness companies source heart rate sensors from different companies, and some of those sensors aren’t all at the same level. Think of them like smartphone displays — you might have a nice AMOLED display on your Samsung and LG phones, but one of them is a few generations ahead of the other.

Steps and heart rate are just two metrics. Fitness trackers also estimate caloric burn, sleep stages, and more. All of these metrics will look slightly different on every tracker you wear and how you wear it.

“But I’m paying a company to track my activity! I should expect them to do it accurately.”

No, no, I hear you. You’d like to spend money on something that works the way it’s intended. I, too, want fitness trackers to be more accurate, but that’s just not the world we live in.

As a general rule, we should put more importance on the major trends our fitness trackers pick up, rather than taking each metric as fact.

It's more important for wrist-based heart rate sensors to pick up on major trends, rather than being 100% accurate.

If your heart rate sensor catches a quick downturn in your heart rate when you take a walk break on your run, isn’t that more important than being 100% accurate? Personally, I’d say so.

Also, the number of steps we take in a day is a fine metric to track, but it doesn’t always tell the best story of your overall health. According to the World Health Organization (WHO) and American Heart Association (AHA), we should all strive for 150 minutes of moderate and 75 minutes of vigorous activity each week. Companies like Fitbit and Google are centering their activity tracking around these metrics within the Fitbit app and Google Fit. I wouldn’t be surprised if more companies followed suit in the future. It just makes more sense to track the duration of our exercises.

“How can I improve my fitness tracker’s accuracy?”

An image of the Garmin Venu 2 Plus on the wrist showing Body Battery graphs and metrics
Jimmy Westenberg / Android Authority

If you’re going through the trouble to wear one of these devices every day, you might as well make the most of it. How do you make your fitness tracker track things more accurately?

The best suggestion I have is to follow the manufacturer’s guidelines. I don’t want to be the guy that tells you to read the little instruction manual that comes with your smartwatch, but you should probably skim it just in case there are some good tips in there. Companies have tips posted online, too, and many of the bigger fitness companies have forums you can join to learn more about your tracker.

If you really don’t want to do any of those things, here are a few general guidelines you can follow to make your device more accurate.

  • Wear your fitness tracker firmly on your wrist: Your fitness tracker will have a much harder time telling movements apart while it’s moving from one end of your wrist to the other. This is especially important for heart rate sensor accuracy. Try to tightly strap your watch to your wrist so it doesn’t move, but not so much that it becomes uncomfortable.
  • Don’t wear your fitness tracker on your dominant wrist: Your fitness tracker should attempt to ignore any movements that aren’t associated with normal walking or running activities, but, as mentioned, no device is perfect. The simple fact is that your non-dominant wrist will probably move less frequently than your dominant wrist throughout the day, so you want to cut down on those ghost movements wherever possible.
  • Tweak settings like stride length in your fitness tracker companion app: Everyone moves their bodies differently. Most fitness applications let you tweak certain things like stride length to allow your wearable to keep track of things more accurately. If you take longer or shorter than average strides for your body type, you might want to change these settings in your fitness app. Certain apps also let you change sleep tracking sensitivity, automatic activity recognition, and more.
  • Buy the right gear: Most trackers nowadays can record a few baseline metrics, but they’re not all created equally. Don’t buy a Xiaomi Mi Band if you want accurate running metrics; instead, buy something from Garmin, Polar, Suunto, or even from Apple. On the other hand, you probably don’t need to buy a $500 GPS running watch if you just need a decent way to track your steps. And if you’re looking for the most accurate heart rate metrics you can find, you’ll want a heart rate sensor chest strap.

Ultimately, fitness devices are highly personal, functional, and oftentimes affordable pieces of tech that really can track an insane amount of data. While I’m certainly not trying to dismiss the legitimately useful features each one of them offers, I think it’s important to keep the limitations in mind.

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