Researchers recently conducted a study to evaluate activity trackers in estimating the activity levels of patients with hemophilia (PWH). They concluded that the Fitbit Charge 3 (Fitbit Inc, San Francisco, CA) tended to overestimate the number of steps walked and the minutes of physical activity (PA) in this population, in comparison with a research-grade accelerometer. They reported the study results in the journal Haemophilia.

PA has been identified as providing some health benefits for PWH, and activity monitors, such as the ActiGraph GT3X-BT accelerometer (ActiGraph LLC), have been in use in research to monitor the activity level of PWH. However, consumer-grade activity monitors have also come into use, both in research and by the general public. The research team conducting this study aimed to determine the accuracy of the consumer-grade Fitbit Charge 3, in comparison with the ActiGraph GT3X-BT, in chronicling the activity of PWH.

This analysis was performed as a component of a larger study, the HemFitBit study, examining PA in the setting of hemophilia in young patients in Norway ( Identifier: NCT04181697). For this analysis, patients wore an ActiGraph GT3X monitor on the right hip, and simultaneously they wore a FitBit Charge 3 on the nondominant wrist. Devices were worn, in free-living conditions, for 7 consecutive days. The researchers analyzed patterns of agreement in results of activity measurements between the devices.

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There were 20 male PWH included in the analysis, and they had a mean age of 21.8 years (SD, 6.6). Severe hemophilia was present in 19 of the patients, and the mean Hemophilia Joint Health Score was 7.0 (SD, 6.7). Patients had a mean body mass index of 24.3 kg/m2 (SD, 5.1).

Overall, the researchers reported that the 2 types of activity monitors demonstrated moderate or higher correlations for daily averages in all PA metrics that were tested. The measured number of steps, for example, showed a Pearson’s correlation coefficient between device types of 0.91, which the researchers considered to reflect an excellent level of correlation. However, differences in results between the 2 types of devices were statistically significant across most examined measures, although they were similar for the daily minutes of moderate PA that were reported by both device types.

The researchers considered various measures of PA to be overestimated by the Fitbit Charge 3. These included the average daily steps and the minutes of PA in light, vigorous, and moderate-to-vigorous categories. Higher amounts of PA were also reportedly linked to higher levels of overestimation using this device.

“Although the Fitbit Charge 3 appears to overestimate PA parameters compared to the research-grade ActiGraph accelerometer, it is still more objective than self-report assessment of PA and valid for surveillance of PA over time within an individual,” the researchers noted in their report. However, given the results they observed in this study, the researchers recommended that users be aware of the potential for differences in results obtained with these different types of devices.

Disclosures: Some authors have declared affiliations with or received grant support from the pharmaceutical industry. Please refer to the original study for a full list of disclosures.


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