Validity of Consumer-Based Physical Activity Monitors

Jung-Min Lee; Youngwon Kim; Gregory J. Welk


Med Sci Sports Exerc. 2014;46(9):1840-1848. 

In This Article

Abstract and Introduction


Background: Many consumer-based monitors are marketed to provide personal information on the levels of physical activity and daily energy expenditure (EE), but little or no information is available to substantiate their validity.

Purpose: This study aimed to examine the validity of EE estimates from a variety of consumer-based, physical activity monitors under free-living conditions.

Methods: Sixty (26.4 ± 5.7 yr) healthy males (n = 30) and females (n = 30) wore eight different types of activity monitors simultaneously while completing a 69-min protocol. The monitors included the BodyMedia FIT armband worn on the left arm, the DirectLife monitor around the neck, the Fitbit One, the Fitbit Zip, and the ActiGraph worn on the belt, as well as the Jawbone Up and Basis B1 Band monitor on the wrist. The validity of the EE estimates from each monitor was evaluated relative to criterion values concurrently obtained from a portable metabolic system (i.e., Oxycon Mobile). Differences from criterion measures were expressed as a mean absolute percent error and were evaluated using 95% equivalence testing.

Results: For overall group comparisons, the mean absolute percent error values (computed as the average absolute value of the group-level errors) were 9.3%, 10.1%, 10.4%, 12.2%, 12.6%, 12.8%, 13.0%, and 23.5% for the BodyMedia FIT, Fitbit Zip, Fitbit One, Jawbone Up, ActiGraph, DirectLife, NikeFuel Band, and Basis B1 Band, respectively. The results from the equivalence testing showed that the estimates from the BodyMedia FIT, Fitbit Zip, and NikeFuel Band (90% confidence interval = 341.1–359.4) were each within the 10% equivalence zone around the indirect calorimetry estimate.

Conclusions: The indicators of the agreement clearly favored the BodyMedia FIT armband, but promising preliminary findings were also observed with the Fitbit Zip.


Accelerometers have become the standard method for assessing physical activity (PA) in field-based research.[23] They are small, noninvasive, and easy to use, and they provide an objective indicator of PA over extended periods. They have been used almost exclusively for research, but advances in technology have led to the emergence of new consumer-based activity monitors designed for use by individuals interested in fitness, health, and weight control. Examples include the BodyMedia FIT (BMF), the Fitbit, the DirectLife (DL), the Jawbone Up (JU), the NikeFuel Band (NFB), and the Basis B1 Band (BB). The development of these consumer-based monitors has been driven in large part by the increased availability of low-cost accelerometer technology in the marketplace. The refinement of other technology (e.g., Bluetooth) and the increased sophistication of personalized social media applications have also spurred the movement. These new accelerometry-based monitors provide consumers with the ability to estimate PA and energy expenditure (EE) and track data over time on Web sites or through cell phone applications.

Other technologies have also been adapted to capitalize on consumer interest in health and wellness. Pedometers developed originally to measure steps have been calibrated to estimate EE and to store data over time.[1] Global positioning system monitors, developed primarily for use in navigation, are now marketed to athletes and recreation enthusiasts to monitor speed and EE from the activity. HR monitors, originally marketed to athletes, have also been modified and marketed to appeal to most recreational athletes interested in health and weight control. Although the functions and features vary, all of these devices attempt to provide users with an easy way to objectively monitor their PA and EE over time.

The increased availability of monitoring technology provides consumers with options for PA self-monitoring, but these tools may also have utility for applied field-based research or intervention applications designed to promote PA in the population. However, little or no information is available to substantiate the validity of these consumer-based activity monitors under free-living conditions. It is important to formally evaluate the validity of these various devices so consumers, fitness professionals, and researchers can make informed decisions when choosing one of the monitors. Research on PA assessment has progressed by continually evaluating new technologies and approaches against existing tools. The present study adds new information to the literature by formally evaluating the validity of eight different consumer-based, activity-monitoring technologies under semistructured free-living conditions, with estimates of EE from a portable metabolic analyzer as the criterion measure.