Fitness trackers are effective tools to measure heart rate, but leave room for improvement when measuring calories, according to a study in Journal of Personalized Medicine.
The study — led by researchers from Stanford (Calif.) University and The Swedish School of Sport and Health Sciences in Stockholm — compared the accuracy of seven commercial fitness trackers. The researchers evaluated Apple Watch, Basis Peak, Fitbit Surge, Microsoft Band, Mio Alpha 2, PulseOn and Samsung Gear S2.
Sixty volunteers wore the fitness trackers while sitting, walking, running and cycling. The researchers assessed the devices' accuracy when recording heart rate and energy expenditure — which commercial trackers often refer to as the amount of calories a user has burned — for each volunteer and activity.
The devices experienced the fewest errors for cycling and the most for walking. Six of the seven devices had a median heart rate error below 5 percent for cycling. None of the devices recorded an energy expenditure error below 20 percent. Overall, the Apple Watch had the fewest errors for both heart rate and energy expenditure. Samsung Gear S2 had the most.
Fitness tracker errors also varied by volunteers' gender, body mass index and race.
"In conclusion, most wrist-worn devices adequately measure [heart rate] in laboratory-based activities, but poorly estimate [energy expenditure], suggesting caution in the use of [energy expenditure] measurements as part of health improvement programs," the study authors concluded. "We propose reference standards for the validation of consumer health devices."