Why you can’t trust your fitness tracker to burn calories

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There was a time, before applying Fitbits, when no one knew how many calories they were burning per day. Sure, you can calculate a rough estimate based on your body size, gender, and age; And you can choose whether or not to believe the calorie readings on the treadmill and bikes at the gym. But the idea that a device can tell you what’s going on you personally burn on This whole day It was revolutionary. As was a mistake. still wrong.

How fitness trackers calculate calories burned

Before we think about how accurate fitness trackers are, let’s take a look at what they actually do. Most trackers use accelerometers to know when and how much your body is moving. If you have a watch on your wrist, and the watch oscillates harmoniously back and forth while hopping up and down, your gadget is guessing that you must be walking. If there is a faster bounce and your wrist makes a smaller movement, you are probably running.

This is the basic idea behind how trackers detect how many steps you’ve taken. If you’ve ever paid attention to your step count, you already know some of the ways this can be inaccurate. If you’re shopping, for example, keeping your hand on the handle of a shopping cart may result in you not getting credit for the steps you take. (A wearable that clips to your torso would be more accurate, but manufacturers seem to be moving away from the clip-on type.)

Then there is the heart rate sensor. Since your hands don’t always move predictably during a workout, it may be easier to just tell your watch that you’re going to bike, do yoga, or something else. The tool then uses your heart rate to guess how much work your body is doing.

Whatever the data source – heart rate, movements, or range – the tool uses an equation to calculate how many calories it thinks you’re burning. Your age, weight, and gender may enter into this equation. So a fitness tracker doesn’t actually do that I know How many calories do you burn Instead, a number is calculated based on incomplete information.

Factors that can affect the accuracy of a fitness tracker

If we are robots, we all build the same thing, we all move in predictable patterns, then this approach might work. But humans are complex, and technology is often confused.

For example, you may get a different number of steps If you put a tool on your right wrist opposite your left wrist. and optical heart rate sensors used by many trackers Less accurate on dark skin.

These issues have to do with the data the trackers collect, but then there’s the question of how the algorithms put it together to get the number they show you when you figure out how many calories you’ve burned. Companies that make fitness trackers are not required to publish their algorithms or verify the accuracy of their calorie counts. They can just put a device on the market and there you are, comparing wearables on shopping sites without any information about their accuracy, aside from the companies’ claims.

Researchers are interested in the accuracy of fitness trackers, which might sound like a good thing. They want to be able to use wearables in research or recommend them to individuals and health care providers.

But there is significant delay in actually getting this information, and it is often published too late to be useful. By the time a researcher buys a set of the latest model, conducts his study, writes it down, submits it to a journal, and finally publishes it, several years may have passed and the company has moved on to the next model.

With that caveat, I still think it’s worth taking a look at some research on fitness trackers, to see what kinds of traits come up. be Which Which of them is good at estimating calories burned?

What studies say about the accuracy of fitness trackers

Well, time for the bad news. a Study from 2020, which looked at a variety of gadgets including Apple, Garmin, Polar and Fitbit products, found that all devices are inaccurate more often than they are. The authors considered the device accurate if its reading was greater than or less than 3% when compared to a more accurate measure of energy expenditure (ie, calories burned) in a laboratory setting. Here’s how some of the top brands are performing:

  • Garmins burns calories 69% of the time.
  • Apple Watches burn calories 58% of the time.
  • Polar devices overestimate calories burn 69% of the time.
  • Fitbits underestimated 48% of the time and overestimated 39% of the time.

The fact that the Fitbits were almost correct in the middle Not that it was useful. If your device sometimes overestimates it and sometimes underestimates it, it won’t be very useful unless you know which is which.

a A 2018 review specifically from Fitbits I found that accuracy varies greatly depending on factors such as where you wear it (the torso was more accurate than the wrist), whether you walked uphill, and whether you walked at a steady speed or stopped and started. Accuracy also varies by device, as the Fitbit Classic underestimates calorie burn and usually overestimates the Fitbit Charge. Devices aren’t accurate enough to know how many calories you’re actually burning

a Newer study, published earlier this year, compared the Apple Watch 6, Fitbit Sense, and Polar Vantage V. The researchers had volunteers wear the three gadgets while quietly sitting, walking, running, cycling and strength training. Each instrument, for each activity, was given a judgment of ‘poor accuracy’ with variance coefficients ranging from 15% to 30%.

If all of these devices are imprecise, how do I know how many calories I’m burning?

It’s probably more useful if you think calorie burn is a number that you can’t measure directly. Treat it like a black box: I’m burning Some unknown numbers Calories, what now?

The only common reason you need an accurate estimate of your calorie burn is if you’re trying to figure out how much food you need to eat. If you want to lose weight, you want it Eat less than you burn; If you want to gain weight, you want the opposite; And if you’re trying to make sure you’re maintaining your weight, you’ll want to eat roughly the same amount you burn.

The cool thing is that you can adjust how much you eat directly on your weight, rather than using calorie burn estimates as a proxy. Let’s say you’re training for a marathon and want to make sure you’re fueling yourself appropriately. Well, if you are undereating, you will start to lose weight. When you start seeing the scale trend downward, this is your signal to add a few hundred calories to your diet. If your weight remains stable after this adjustment, you know you are eating the right amount. The more you train (or if you take time off to relieve a sprained ankle), the more adjustments you can make as you progress.

have post here It details how to make these adjustments with the help of either a paid app, a set of free apps, or a DIY spreadsheet. If you’re using a fitness tracker instead, and it’s working for you, feel free to keep using it. But if the tracker stops giving you the results you want, go ahead and leave it out of the equation.