‘Faulty’ fitness trackers make you go that extra mile

FITNESS trackers exaggerate how far you have actually run, a study has found. According to new research by the consumer group Which? some wearable devices under or overestimate distances by more than a third.

For runners in yesterday’s 26.2-mile London Marathon this could mean missing the finish line by eight miles.

Well-known brands such as Samsung were found to show incorrect distances and missed the marathon line by an average of four miles.

Which? tested more than 85 fitness trackers and smartwatches, with prices reaching up to £500, to find the most and least reliable. Each was assessed for accurately measuring track steps, distance based on steps, heart rate and calories burned.

The Garmin Forerunner 35 and Misfit Ray fitness tracker were only 68 per cent accurate, showing 17.8 miles when the actual distance run was 26.2 miles.

If the product had failed to work on yesterday’s marathon it would have been the equivalent of the runners having to go eight miles beyond the finish line.

Which? said some fitness trackers that do not have built in GPS and calculate distance by the number of steps taken. Usually this will be based on an estimated stride length multiplied by footfalls, but some trackers do not allow stride length to be altered, which hits their accuracy.

Models with GPS are the most accurate, but even they could be up to 20 per cent out in Which? tests.

Some devices without GPS will use the sensor on a mobile phone to track distance.