The researchers suggest that although the heart rate measurements are pretty much accurate, energy expenditure measurements are probably significantly wrong.
Apple Watch, Basis Peak, Fitbit Surge, Microsoft Band, Mio Alpha 2, PulseOn and Samsung Gear S2 were tested in a group of 60 people. The results showed that measuring heart rate had an error rate of less than 5% on 6 of the devices. Some measurements were more accurate than others while skin color and body mass index affected measurements.
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