Newswise — Wearables such as the Fitbit are popular and can be used to self-monitor and promote physical activity. Therefore, it is important to know how well the devices measure activity throughout the day. So far, such studies have been conducted in labs or were only focused on determining total activity over the whole day. The current study examined the Fitbit One, using smaller time intervals, such as hour-by-hour intervals and minute-by-minute intervals. Results showed that while the Fitbit One is a good instrument to measure number of steps taken, it does overestimate daily step activity. Compared to a well-accepted research device, the Fitbit One, on average, moderately overestimated steps by 0.82 each minute or by 677 in a full day. However, compared to the research device, the Fitbit was less accurate in measuring the intensity of the activity - that is, less able to sort out whether the activity is of light, moderate, or vigorous intensity. Given that the research device used in the current study cannot be considered a flawless measure of activity intensity, it could be that the Fitbit One could be better in measuring the activity intensities. The conclusion of this study is that the Fitbit One can be used to self- monitor step activity, but one should be careful with interpreting the intensities.

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American College of Sports Medicine’s (ACSM) annual meeting