The bit doesn’t fit: Evaluation of a commercial activity-tracker at slower walking speeds

• Published in: Gait & posture 2018-01, Vol.59, p.177-181
• Main Authors: Wong, Christopher K., Mentis, Helena M., Kuber, Ravi
• Format: Article
• Language: English
• Subjects: Accelerometers; Adult; Equipment Failure Analysis; Exercise Test; Female; FitBit; Fitness Trackers - standards; Humans; Male; Middle Aged; Older adults; Reference Values; Reproducibility of Results; Software; Step count; Walking Speed; Young Adult
• ISSN: 0966-6362; 1879-2219
• DOI: 10.1016/j.gaitpost.2017.10.010

•The FitBit Ultra was evaluated in four minute trials of treadmill walking at three slow and average walking speeds of 25 participants.•Step counts per minute were extracted from the FitBit API and directly compared to observed counted steps based on video analysis.•At the slowest speed, 0.9m/s, accuracy reduced most significantly, with 11 participants recording zero step counts.•Caution should be used when using the FitBit Ultra with slower walking populations if step-count accuracy is a crucial factor. Accelerometer-based commercial activity trackers are a low-cost and convenient method for monitoring and assessing health measures such as gait. However, the accuracy of these activity trackers in slow walking conditions on a minute-by-minute basis is largely unknown. In this study, the accuracy of a hip-worn commercial activity tracker (FitBit Ultra) was examined through step counts. Accuracy was evaluated through four minute trials of treadmill walking at speeds representative of older adults (0.9, 1.1, and 1.3m/s). Minute-by-minute step count was extracted through the FitBit API and compared it to observer counted steps through video recordings. Results highlighted a significant over-reporting of steps at the highest speed, and a significant under-reporting of steps at the slowest speed, with the FitBit Ultra failing to count steps for one or more minutes at the slowest speed for 11 participants. This study highlights problems with using the FitBit Ultra by slow-walking populations, and recommends that researchers and clinicians should carefully consider the trade-off between accuracy and convenience when using commercial activity trackers with slow-walking populations.