Do you swear by that tiny little device on your arm? Obsessively watch it's every move for the step count to go up? No, us neither, obvs. But, if you do, now might be the time for a rethink.
Scientists put seven of the most popular devices to the test and found they were good at measuring heart rate, but poor at measuring calories burned. Which, whatever way you look at it, is pretty annoying.
The study asked 60 male and female volunteers to walk, run and cycle using the trackers. Researchers found that six out of seven of the fitness devices had an error rate under 5% for estimating heart rate, yet when it came to calories burnt throughout the day results were way off (the lowest at 27.4% for the FitBit Surge to the highest of 92.6% for the PulseOn device).
So, why such a difference? It's down to a range of factors, naturally, and not just that your Fitbit is lying to your face every day.
There could be a problem with the device's algorithm or the data you input might be wrong. There's also the issue of everyone who uses a tracker has a different body type/shape, so it's hard to train an algorithm to give an accurate result across a wide variety of people.
Oh-so helpfully, the devices proved most accurate for white women who were already fit. Meaning for those of us who, y'know, are actually trying to lose weight, the error was greater.
Bottom line: take your fitness tracker's calorie counts with a pinch of salt/pizza.