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  • Post published:08/04/2021
  • Post last modified:08/04/2021

I was pretty puzzled by the Which? investigation into fitness trackers last week. With the London Marathon happening today, they decided to run a check on the trackers, which can record your distance, pace, heart-rate and location.

Some 118 trackers were tested over a marathon distance – 26.2 miles (42km) – and they found that some trackers underestimated the distance whilst some overestimated. The Garmin Vivosmart 4 underestimated the distance by 10.8 miles, meaning that the person testing it ran 37 miles instead of 26.2.

However, what confused me is the fact that all of these trackers were only wrong when they were tested indoors on a treadmill.


That’s been the case for quite some time. Fact is, when you’re inside and you’re effectively not moving anywhere, there’s no GPS track and no real way for the tracker to accurately record your distance. It has to make a guess based on your stride length. Indeed, a spokesman for Huawei pointed this out to Which? by stating..

With regards to running indoors, as this particular test was carried out on a treadmill, the algorithm of Huawei Watch 2 Sport calculates the user’s stride length from the acceleration sensor data while running at different speeds.

This is why, and it’s something any gym-bunny will know, you always rely on the actual distance shown on the treadmill itself. The treadmill knows how fast it’s operating and how far you’ve actually run. You can’t rely on your tracker for that.

Most trackers are great at step-counting, heart-rate monitoring and showing how many calories you’ve burned. If you’re using your heart-rate monitoring at the gym then this will definitely be more beneficial. Also, if they have GPS, they’re good at tracking your runs, cycles and outdoor swims.

Inside though? When the GPS data either isn’t available or says you’re static? Best rely on the treadmill on-screen display.

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