Researchers compared the consumer-grade Fitbit Charge 3 device and the research-grade ActiGraph GT3X-BT in young people with hemophilia and found that the Fitbit Charge 3 overestimated average daily steps and the number of minutes of light, moderate-to-vigorous, and vigorous physical activity, as published in Haemophilia. They noted that the bias of the Fitbit Charge 3 increased with the volume of physical activity.

“The validity of various Fitbit models has been investigated both in laboratory and free-living settings, including healthy participants as well as people with various chronic diseases and with mobility limitations, but not [people with hemophilia],” the authors explained.

“Previous Fitbit models have been compared to ActiGraph accelerometers specifically, but to the best of our knowledge, there has not yet been performed such an evaluation of the Fitbit Charge 3′s accuracy.”

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The research team assessed the 2 devices in 20 male patients (8 teenagers and 12 adults) with hemophilia over a 7-day measurement period. Nineteen of the participants had severe hemophilia and low hemophilia joint health scores. The results showed that, compared with the ActiGraph, the Fitbit reported a higher average number of daily steps and more minutes of low, moderate, and vigorous physical activity.

Although there was an excellent correlation between the 2 devices in measured steps, there was a significant mean difference of 3388 steps between them, and the difference was greater as the number of steps increased.

Furthermore, the Fitbit significantly overestimated the daily minutes of exercise at all levels compared with the ActiGraph. The authors note that the discrepancies could be due to the location the device is worn, different measurement properties, filtering algorithms, and different physical activities performed.

The Fitbit is still considered better than self-reports on physical activity and is more convenient to wear than the hip-worn Acti-Graph, therefore the team does not suggest the Fitbit should be discarded but rather that clinicians and patients should be aware of the potential overestimation of physical activity by the device.


Matlary, RED, Holme, PA, Glosli, H, Rueegg, CS, Grydeland, M. Comparison of free-living physical activity measurements between ActiGraph GT3X-BT and Fitbit Charge 3 in young people with haemophilia. Haemophilia. Published online July 13, 2022. doi:10.1111/hae.14624