The 10,000 step challenge has motivated many to get more active – but what is the accuracy of step trackers like Fitbit?
Increased technology and convenience have led to increased sedentary behaviours – people moving less and sitting more. During the 1970s, two out of 10 working jobs were considered ‘lightly active’—predominantly sitting at a desk. Today, the number of sedentary and light-activity jobs has more than tripled. As a consequence of less daily human activity, incidence of chronic conditions around the globe have significantly increased. There is accumulating evidence to support how habitual inactivity can increase the risk of cardiovascular disease, obesity, cancers, and more.
Current global health recommendations, as outlined by the World Health Organization, suggest that adults aged 18-64 should do a minimum of 150 minutes of moderate-intensity aerobic physical activity throughout the week. Achieving a 10,000 step per day goal is considered Active adults can be categorized as completing 10,000 steps per day.
In an attempt to inspire adults to move and engage in more physical activity, technology companies have developed accessible, user-friendly pedometers—portable electronic devices which use hand/hip motions to count steps. The popular 10,000 step per day goal signifies a step in the right direction, classified as ‘active’ rather than ‘sedentary’, which is classified as less than 5,000 steps per day. But what is the accuracy of health trackers like Fitbit for step counting?
Fitbit has the largest market share for activity monitors worldwide and has sold over 25 million devices. These devices are useful in measuring walking or running and can be connected to an online database allowing users to monitor their activity output as well as interact with other users. Instant activity feedback and moral support of peers over social media platforms have facilitated positive behavioral changes in increasing physical activity. In addition to tracking movement, other health information, such as heart rate, sleep tracking, and nutrition, can be stored in the Fitbit app, generating well-rounded health-conscious user data.
To test one of these devices – the Fitbit Flex -researchers in Cairns, Australia studied the validity and reliability of the device.
Accuracy of Fitbit Flex step counting?
Capabilities of the Fitbit flex were measured against direct laboratory observations and against the Actigraph GT3X+ to test how accurate it is for step counts in free-living environments and for overall moderate-to-vigorous physical activity (MVPA) and activity energy expenditure (AEE). The Actigraph GT3X+ has previously been validated against laboratory studies in its ability to measure step counts and estimate energy expenditure. Twenty-five students were recruited from James Cook University, from June to August 2014. The participants were free of illness or any underlying medical conditions that could hinder their exercising capability. Baseline assessments: height, weight, and body fat percentage were made prior to initiation of the study. Participants were then fitted to a wrist-worn Fitbit Flex and a hip-worn Actigraph GT3X+ accelerometer. As the two devices were worn differently, data for each was evaluated with respect to its optimal device placement.
Two laboratory data collection sessions were conducted. The first exercise protocol required filming participants performing six-minute bouts of walking, incline (5%) walking, jogging, and stair stepping. Following the in-lab exercises, subjects were instructed to wear their devices for the reminder of the day. The second session was completed later in the week—the same exercise protocol was repeated with replicated walking and jogging speeds from the first session. To analyze whether the Fitbit tracker was accurate for step counting, two researchers reviewed the video footage and counted the number of participant steps which were then averaged to a single count. Statistical analysis of MVPA and AEE was done through ActiLife Data Analysis Software by assessing measured device counts per minute. The Fitbit Flex only measures total energy expenditure, thus in order to allow for comparability to the Actigraph, AEE was calculated by subtracting subject basal metabolic rate from total energy expenditure.
Compared to direct observations and the Actigraph, the Fitbit Flex had larger data variability in step counts. The greatest difference was observed for walking—average Fitbit numbers were 15% lower compared to direct observation. Within the six-minute walking period, Fitbit estimates ranged as low as 283 steps and as high as 75 steps to direct observations. Outside of the laboratory environment, the Fitbit had lower step-count estimates in free-living conditions and overall high measurement differences against the Actigraph. Though, for jogging the Fitbit was more comparable to direct observation than the Actigraph. The averaging of both Fitbit data collections demonstrated differences by over 3,000 steps. Fitbit AEE estimates were repeatedly higher and the MVPA minutes lower in comparison to the Actigraph.
Generally, the Fitbit tended to be less accurate with less steps but had increasing accuracy with increasing number of steps. The Actigraph data was significantly correlated with direct observations with the exception of stair stepping. The Actigraph had less measurement discord with direct observations—its step counts ranged from undercounting by 22 steps and overcounting by 94.
The results of this study suggest that the Fitbit has moderate validity compared to direct observation and the Actigraph. It under- or over-counted steps depending on the type of activity being performed. Recent studies reveal that wrist worn accelerometers are less accurate than waist worn ones. However, when assessing their usability, the pros and cons of each must be taken into consideration. When wearing your Fitbit there is decreased wear and tear—due to less need for continuous equipment removal, it easy to sleep with, and it provides instant feedback.
Real-time fitness data helps to encourage overall health and wellness
Scientists have identified links between physical labor, energy expenditure, and health. Fitness trackers, such as the Fitbit Flex, help encourage more physical activity in hopes of decreasing sedentary behaviors. Tracking your steps provides real-time data on calories burned and overall activity, which can aid in improving health and wellness. Further assessment of Fitbit trackers is required to optimize its function and provide a cost-effective health tool to consumers.
Written by Melody Sayrany
- Owen, N., Sparling, P. B., Healy, G. N., Dunstan, D. W., & Matthews, C. E. (2010). Sedentary Behavior: Emerging Evidence for a New Health Risk. Mayo Clinic Proceedings, 85(12), 1138-1141. doi:10.4065/mcp.2010.0444
- Sushames, A., Edwards, A., Thompson, F., Mcdermott, R., & Gebel, K. (2016). Validity and Reliability of Fitbit Flex for Step Count, Moderate to Vigorous Physical Activity and Activity Energy Expenditure. Plos One, 11(9). doi:10.1371/journal.pone.0161224
- Physical Activity and Adults. (2015, June 19). Retrieved October 04, 2020, from https://www.who.int/dietphysicalactivity/factsheet_adults/
- Australia’s Physical Activity & Sedentary Behaviour Guidelines for Adults (18-64 Years). (n.d.). Retrieved October 04, 2020, from https://www.10000steps.org.au/articles/australias-physical-activity-sedentary-behaviour-guidelines-adults-18-64-years/
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