Fitness trackers 'poor at measuring calories burned'

A new report says fitness trackers don't measure the calories our body burns while exercising so accurately. This means people may make poor decisions about their diet. The study, from Stanford University, evaluated five popular trackers. These included the Apple Watch, Fitbit Surge and Samsung Gear S2. The researchers observed 60 volunteers as they walked, ran and cycled with the devices. Researchers found that none of the devices had an error rate below 20 per cent. Dr Euan Ashley said: "People need to know that on energy expenditure, [the trackers] give rough estimates."

The scientists said users of fitness trackers should be careful about using the devices to judge what they eat. Dr Ashley said: "If you go to the gym, and you think you've lost 400 calories, then you might feel you've got 400 calories to play with." This could be a problem for people who decide what to eat after reading fitness tracker data. A CEO of a fitness tracker company told the USA Today newspaper that the study method could have used incorrect settings and thus given incorrect data. He said the study's error rate was wrong because of a "methodological error" in the research.