Accuracy and Reliability of the FitBit ChargeTM Activity Tracker Among Older Adults

Michael Smith, Melissa Powers, Olivia Henderson, Theresa Bodman


Wearable technology, including activity trackers, remains a top fitness trend world-wide; however, the ability of individual activity trackers to accurately and consistently record physical activity remains unknown. The purpose of this study was to evaluate the accuracy and reliability of step counts from the Fitbit Charge™ among older adults. Thirteen participants with a mean age of 70.38 ±4.27 years volunteered to participate and completed all testing. Participants completed a 96 meter walk around a gymnasium while wearing the Fitbit Charge™ activity tracker.

Step counts on the activity tracker were recorded before and after the walk to determine the step count. Each walk was also video recorded to determine the actual number of steps taken during the walk. Step counts from video analysis were confirmed by two researchers. The same procedures were repeated on a second, non-consecutive day of testing to determine the reliability of the activity tracker. Accuracy of the activity tracker was determined by comparing step counts reported by the Fitbit Charge™ to the observed step counts from each testing session. The reliability of the activity tracker was determined by correlation analysis and comparison of step counts from the first testing session to the second testing session. The activity tracker significantly underestimated observed steps at both testing sessions by 21.31 steps and 22.62 steps, respectively (p < .05). No difference in step count from the activity tracker was seen from session one to session two (151.85 steps vs. 152.54 steps, p > .05); however, the correlation between the two sessions was only moderate, r = .55, p = .05. Among older adults, the Fitbit Charge™ appears to underestimate steps taken even over a short distance. The reliability of the Fitbit Charge™ is questionable given only a moderate correlation between sessions. While preliminary, these results call into question the accuracy and reliability of daily step counts from the Fitbit Charge™. It is suggested that all new activity trackers to hit the market are given careful study to determine their ability to accurately measure daily activity.

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