Unreliable Fitness Trackers Add 10 Miles to Your Marathon Route

By Holly Brockwell on at

Listen up, marathon runners: the fitness tracker you use to record your training really matters. A new report by Which? has shown that some of the big name trackers on the market are actually rubbish at recording distance, and can have you running miles more than you need to.

The least accurate wearable in the tests came out as the Garmin Vivosmart 4. A Which? researcher on a treadmill had to run 37 miles before the watch said they'd run the 26.2 miles that make up a marathon.

While Garmin's hapless tracker underestimated distance by over 40%, adding almost 11 unnecessary miles, other trackers overestimated how far the researcher had run. The Huawei Watch 2 Sport, for instance, added 28% to the total -- as Which? puts it, "if this fitness watch reported 26.2 miles travelled on marathon day, you’d actually find yourself around the 19 mile mark near Canary Wharf."

Here are the worst wearables for distance accuracy:

Image: Which?

Garmin said its Vivosmart 4 tracker didn't do well because it doesn't have GPS, as it's intended to be more of an all-rounder. Its dedicated running trackers, like the Forerunner range, are apparently much more accurate -- and the Vivoactive 3 scored 100% on Which?'s tests.

While it's not surprising to techies that less specialist smartwatches and fitness trackers might not give an accurate result, it's not common knowledge that tracking varies this much between models. A dedicated marathon runner would no doubt have a specialist piece of kit, but someone running for the first time might not realise they've been running way too far or not far enough in their training, and that could have serious consequences on marathon day.

Read the full results of the study here, or if you'd rather just know which trackers actually are worth the money, check out our buying guide here. [BBC]