Fitness trackers accurately measure heart rate but not calories burned

Published May 29th, 2017 - 08:04 GMT

Fitness trackers, which have become hugely popular among all age groups of late, may be good at assessing heart rate somewhat accurately but the same cannot be said about their calorie tracking capabilities, according to a new study that covered seven devices.

A team of Stanford researchers, said in a paper published last week in the Journal of Personalised Medicine that though the devices purport to help users track their calories – daily energy expenditure – the number is often markedly incorrect.
While the least accurate device was off by an average of 93%, the most accurate was off by an average of 27%, the Guardian reported.

Though some manufacturers have suggested that the scientists may not have properly set all the user parameters on the device, the consequences of such large margins of error could, of course, be significant.

People are basing life decisions on the data provided by these devices, as pointed out by Euan Ashley, a professor of cardiovascular medicine at Stanford and co-author of the study. While some margin of error when using such devices is inevitable, the scientists said it should be far lower.

“For a lay user, in a non-medical setting, we want to keep that error under 10%,” Anna Shcherbina, a Stanford graduate student and study co-author, said.

One of the key issues, according to her, was the difference in users’ body compositions, as it is very hard to train an algorithm that would be accurate across a wide variety of people because energy expenditure is variable based on factors including someone’s fitness level, height and weight.

The study did not look at how well devices count steps or monitor sleep or stress. The take-home message, says Ashley, is to not rely on the devices to measure total calories burned. Instead focus on eating what we know is a healthy diet, which is low in sugar and high in fibre, and to “eat not until you are full but until you are no longer hungry.”

A total of 60 volunteers, including 31 women and 29 men, wore the seven devices while walking or running on treadmills or using stationary bicycles.

Each volunteer’s heart was measured 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,” said Ashley, “but the energy expenditure measures were way off the mark. The magnitude of just how bad they were surprised me.”

The take-home message is that a user can pretty much rely on a fitness tracker’s heart rate measurements. But basing the number of doughnuts you eat on how many calories your device says you burned is a really bad idea. And, of course, people should exercise. There is no more important intervention than exercise for the prevention of any number of diseases.

© Gulf Times Newspaper 2022

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