Fitness trackers aren’t very accurate when it comes to measuring heart rate, especially if you’re doing a hard workout, researchers say. This could be risky for people who might push themselves too hard, and frustrating for those who wonder why a short jog makes their heart rate skyrocket.
Researchers recruited 50 healthy volunteers to test four popular fitness trackers for a study published this week in JAMA Cardiology. They connected volunteers to an electrocardiogram (EKG), which is the most accurate way of measuring heart rate. Then, volunteers wore the trackers — the Apple Watch, Mio Fuse, Fitbit Charge HR, and Basis Peak — while exercising on a treadmill at 2, 3, 4, 5, and 6 miles per hour.