You check your smartwatch after a run. Your fitness score has dropped. You’ve burnt hardly any calories. Your recovery score is really low. It’s telling you to take the next 72 hours off exercise.

The worst bit? The whole run felt amazing.

So why’s your watch telling you the opposite?

Ultimately, it’s because smartwatches and other fitness trackers aren’t always accurate.

Smartwatches can shape how you exercise

Using wearable fitness technology, such as smartwatches, has been one of the top fitness trends for close to a decade. Millions of people around the world use them daily.

These devices shape how people think about health and exercise. For example, they provide data about how many calories you’ve burnt, how fit you are, how recovered you are after exercise, and whether you’re ready to exercise again.

But your smartwatch doesn’t measure most of these metrics directly. Instead, many common metrics are estimates. In other words, they’re not as accurate as you might think.

Calorie tracking is one of the most popular features on smartwatches. However, the accuracy leaves a lot to be desired.

Wearable devices can under- or overestimate energy expenditure (often expressed as calories burned) by more than 20%. These errors also vary between activities. For example, strength training,........

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