Hard on the heels of recent research out of MIT Sloan School of Management on how sharing your exercise habits with buddies via a training app or fitness tracker motivates you to train harder comes the news from a Stanford University Medical Centre study which says the info you're sharing with your buddies? May be kind of misleading.

The rise of the wrist-worn fitness tracker as our all-knowing all-tracking wellness, lifestyle and weight management device means we're increasingly relying on a piece of wrist hardware - instead of a trained medical professional - to tell us where our health is it. But just how accurate is it?

In an NPR article, associate professor of medicine at Stanford University Medical Centre, Dr Euan Ashley says patients have started bringing fitness tracker data to appointments which, "They're... asking us to digest... and offer advice about how to avoid cardiovascular disease." Ashley and his colleagues, however, "Didn't know how reliable that data was." So they devised a study involving seven of the most popular fitness tracking devices to chart how accurately the trackers measure heart rate and calories burned.

Ashley says in terms of heart rate the study found the devices to be "surprisingly accurate... Most devices most of the time were 'off' by only about 5 per cent." On the flip side the numbers coming from calories burned was like a crazy equation of two plus two equals a hat. Ashley says, "The degree of inaccuracy (in calories burned) ranged from 20 per cent to 93 per cent of the time, meaning 93 per cent of the time the worst-performing device was wrong." Which is not the best news if you're relying on your not-so-trusty fitness device to tell you whether you've burned enough cals on the jogging track to justify that raspberry and white chocolate muffin for morning tea.

So this will change the way you think about fitness trackers