Researchers at Aberystwyth University have claimed some fitness trackers have an "inherent tendency" to overestimate the number of calories burned while walking by more than 50 per cent, according to BBC X-Ray.
The researchers' tests are said to have measured the amount of oxygen used by a volunteer with an oxygen monitor during ten minute walking and running sessions on a treadmill, after which the data was compared to various fitness trackers.
These included the Fitbit Charge 2, Letscom HR and Letsfit according to the BBC report, so "various" is certainly questionable - no Apple, no Garmin, no Withings, as yet, though it's not currently clear if they might be revealed during the BBC show taking place on 28 January at 7:30PM. It's also worth noting the Charge 2 isn't the latest Fitbit - it's over two years old - while Letscom and Letsfit wouldn't be considered "popular brands" in the fitness tracker market.
This report isn't the first to claim fitness trackers overestimate or underestimate some metric though, be it calories, steps or heart rate and it likely won't be the last. Numerous trusted sources like Reuters and Which have also highlighted discrepancies in the past.
The question is however, does it actually matter if fitness trackers aren't spot on with calories burned or if they are a few steps above or below actual steps taken? No, no it absolutely doesn't.
It's important they are within a reasonable parameter of accuracy of course, but fitness trackers are designed as motivational devices not as scientific absolutes.
The majority of people who buy them do so to ensure they are hitting 10,000 steps a day, or to track an elliptical session at the gym, or perhaps see how many hours of deep sleep they got. There will be few who expect a fitness tracker to deliver the levels of accuracy you could only get from being hooked up to numerous wires and medical machines.
The whole point in a fitness tracker is to highlight how much or how little you move and motivate you to do more. They remind you to stand up every hour or walk 250 steps an hour, for example.
So yes, a 50 per cent discrepancy is a surprising result from the likes of Fitbit, especially given its step and heart rate algorithms are great in our experience. But while fitness trackers may offer varying degrees of accuracy in terms of calories burned, or steps taken, or even heart rate, they will give you an estimation and this estimation can be a basis for motivation.
Ultimately, if strapping one of these little devices to your wrist helps you be fitter and healthier, have they not fulfilled their purpose?