Fitness trackers not accurate calorie counters: study

Your fitness trackers can measure heart rate, but are not good at counting how many calories you have burnt, Stanford researchers have found.
An evaluation of seven fitness tracking devices in a diverse group of about 60 volunteers showed that six of the devices measured heart rate with an error rate of less than 5 per cent.
Researchers from Standford University in the US found that in contrast, none of the seven devices measured energy expenditure accurately. Even the most accurate device was off by an average of 27 per cent and the least accurate was off by 93 per cent.

The team evaluated the Apple Watch, Basis Peak, Fitbit Surge, Microsoft Band, Mio Alpha 2, PulseOn and the Samsung Gear S2.
Some devices were more accurate than others, and factors such as skin colour and body mass index affected the measurements, researchers said.
About 60 volunteers, including 31 women and 29 men, wore the seven devices while walking or running on treadmills or using stationary bicycles.

Researchers measured each volunteer's heart with a medical-grade electrocardiograph. Metabolic rate was estimated with an instrument for measuring the oxygen and carbon dioxide in breath - a good proxy for metabolism and energy expenditure.

Results from the wearable devices were then compared to the measurements from the two "gold standard" instruments.
"The heart rate measurements performed far better than we expected, but the energy expenditure measures were way off the mark. The magnitude of just how bad they were surprised me," said Euan Ashley, professor at Stanford University.
The study was published in the Journal of Personalised Medicine.