A says fitness trackers don't measure the we burn while exercising so . This means people may be making decisions about their . Researchers looked at five trackers, including the Apple Watch. The observed 60 as they walked, ran and cycled. None of the devices had an error below 20 per cent. A researcher said the trackers only gave "rough " for calories burned.
The scientists said people should be about using the devices to decide what to eat. A researcher said: "If you go to the , and you think you've lost 400 , then you might feel you've got 400 calories to play with." A of a fitness tracker company said the method could have used settings, which would give incorrect . He said the study's error rate was because of an in the research .