How are fitness trackers accurate?


How do Apple watches, FitBits, etc. accurate? Are they truly precise?

In: Technology

Short answer? They’re not. They use algorithms based on things like movement (steps) to estimate calorie burn to varying degrees of success.

*However*, a good fitness tracker can still be worthwhile. That’s because a good tracker is usually *consistent*. That means that once you get it dialed in, you can use it fairly effectively for things like weight loss.

They’re not very accurate but can provide baselines to track your progress.

The more you spend usually will give you better sensors with more accuracy, but for practical use many of the less expensive ones are good enough for amateur use. Do you need to spend 3x the price for 5 or 10% better accuracy?

I wore a top of the line FitBit on one wrist and a much cheaper Xiaomi Mi Band on the other wrist for a month, switching wrists every week. The results were nearly the same. I returned the FitBit.

Tracking progress is a good motivator, so a usable fitness tracker is a good investment.

To borrow a phrase from a pirate: It’s more guidelines than rules. The fitness isn’t completely accurate as it runs off algorithms and measures off of averages and ranges of data and not necessarily information that specifically pertains to you. They can still be effective and accurate though as long as you use them consistently and don’t try to cheat what they measure.

Accurate regarding which measurement?

Measuring heart rate will be fairly accurate. Inferring calories burned from that measurement … not so much.

If it has GPS (or other GNSS) it will be accurate at measuring speed and distance, assuming you have a good view of the sky. (It will be less accurate when it comes to elevation, unless it has a barometric elevation sensor).

Detecting steps (or even other activities like weight lifting exercises) works by measuring acceleration and trying to match patterns. Measuring acceleration is highly accurate, but the pattern matching is difficult and can be fooled.

Depends on what you mean by accurate. There were a few studies done back in the FitBit heyday that demonstrated that phones were actually *better* at tracking steps and distance (not even including GPS data) than Fitbits. The Apple Watch basically killed all the other fitness trackers.

Tracking steps is pretty easy, and they’re pretty accurate. Tracking distance is also easy via GPS, so they’re accurate for this as well.

Tracking things like heartrate, they’re reasonably accurate. The Apple Watch does a pretty good job, and it has a shockingly good ECG function, but it will be wonky if you’re doing intervals or something and moving/sweating a lot with a very high HR. For that sort of thing the chest-band trackers are still superior.

For things like *calories,* it gets really tricky. It’s effectively making a bunch of assumptions based on your height, weight, sex, age, heartrate, and activity type. I wouldn’t really take any of the calorie estimates seriously, IME they are way overblown. If I *actually* burned 1,000 calories in 90 minutes of weightlifting, I would probably be half-passed out on the floor for 2 hours afterward.

There are ways to track calorie consumption accurately, but they generally involve peeing in a cup or breathing into a tube in a hospital.

So it really depends on what you’re trying to track.