But they are accurate at measuring heart rate, a study of seven devices has found.Read more
In the week of the Great Manchester Run, meet Kelly Harrop - who still loves to run despite having a third of her lung removed after a battle with cancer in 2015....
You can watch live coverage of the Great Manchester Run on Sunday, 28 May from 12:00 BST.
There will also be live coverage of the Great Manchester City Games on Friday, 26 May from 18:00 BST.
Kelly Harrop, who is missing a third of her lung after a battle with cancer in 2015, still loves to run.
Meet 82-year-old Jimmy, who plays Masters Rugby League - which is all based on the colour of your shorts, according to age.
Meet 82-year-old Jimmy, who plays Masters Rugby League - which is all based on the colour of your shorts according to age.
BBC Radio Sheffield
Research has been released today which looks at whether you can be both fat and fit.
A study of 3.5 million Britons suggests that having excess fat increases the risk of suffering heart disease by half, even when blood pressure and cholesterol levels are normal.
To find out a bit more about this I've been out to meet Lucy Arnold who's a personal trainer from Sheffield and her client Jill to see what they think: