JMIR Publications

ABSTRACT

Background:

Although it is widely recognized that physical activity is an important determinant of health there is considerable challenge in assessing this complex behavior. Tools for the objective assessment of the frequency, intensity, and duration of physical activity in adults and children have largely been developed for short-term use within research or public health surveillance environments. However, recent advances in microtechnology, data processing, wireless communication, and battery capacity have resulted in the proliferation of low-cost, non-invasive, wrist-worn devices with attractive designs that can easily be used by consumers to track their physical activity over long periods of time.

Objective:

The purpose of the present systematic-review and meta-analyses is to examine, quantify, and report on the current state of evidence for the analytical validity of energy expenditure, heart rate, and steps measured by recent combined-sensing Fitbits.

Methods:

Systematic-review and Bland-Altman meta-analyses of validation studies of combined-sensing Fitbits against reference measures of energy expenditure, heart rate and steps.

Results:

A total of 52 studies were included in the systematic review. Among them, 41 were included in the meta-analyses, representing 203 individual comparisons between Fitbit devices and a criterion measure (i.e., 117 for heart rate, 49 for energy expenditure, and 37 for steps). Overall, the majority of authors of the included studies concluded that recent Fitbit models underestimate heart rate, energy expenditure, and steps compared to criterion measures. These independent conclusions aligned with the results of the pooled meta-analyses showing an average underestimation of, respectively, -2,99 bpm, -2,77 kcal/min and -3,11 steps/min of the Fitbit compared to criterion measure (results obtained after removing high risk of bias studies).

Conclusions:

Fitbit devices are likely to underestimate heart rate, energy expenditure, and steps. The estimation of these measurements varied by quality of study, age of the participants, type of activities, and by model of Fitbit. The qualitative conclusions of the majority of studies aligned with the results of meta-analyses. Although the expected level of accuracy might vary from one context to another, this underestimation can be acceptable, on average, for steps and heart rate. Information about energy expenditure however are likely to be too unprecise.