Out of puff with miles still to go? Check your fitness tracker

SOME fitness trackers are so unreliable they have been found to miscalculate the distance of a marathon by nearly 11 miles, new research claims.

New analysis by consumer watchdog Which? said fitness trackers from brands including Garmin, Fitbit, Apple and Huawei were unable to accurately track someone running a marathon distance. While some devices undercalculated the distance, others sent runners miles too far.

It comes ahead of the London Marathon, which takes place tomorrow.

Huawei’s Watch 2 Sport left runners well short of a full 26.2-mile marathon, the study claimed, telling the wearer they had reached the milestone after only 18.9 miles. The Apple Watch Series 3 said the target had been hit at 22.8 miles.

Runners using other brands may find they have overtrained, with Garmin’s Vivosmart 4 named the least reliable by the Which? research. It found that by the time the device had clocked the marathon distance of 26.2 miles, runners would have run 37 miles. Samsung’s Gear S2 was also found to miscalculate the distance, saying the wearer had reached marathon distance only after they had run 36.2 miles.

Which? said it carried out its analysis using a calibrated treadmill to compare the ability of different trackers to log steps taken and distance travelled.

In response, Garmin highlighted that the Vivosmart 4 did not use GPS and was not recommended for marathon runners. “Our recommendation … would be to choose a tracking device such as our Forerunner range,” a spokesman said.