Choosing Instruments for Research: an Evaluation of Two Activity Monitors in Healthy Women

Introduction:
Activity-based monitors offer researchers a feasible, quantitative means for the assessing physical activity and sleep quality on a consistent and uniform basis. The purpose of this comparative study was to evaluate the reliability and feasibility of the Fitbit 4.10 activity based monitoring system to the standard actigraph GT3X+ in 42 data points in healthy women.

Methods:
A head-to-head comparison of two activity monitoring systems was conducted using data generated from participants who each wore the two monitors simultaneously for 20-22 hours per day for 14 consecutive days. Outcome variables of interest included both physical activity and sleep quality measurements. Data analysis consisted of descriptive statistics for the sample demographics, one measure of association (Pearson r) and three measures of agreement (intraclass correlation, concordance correlation, and Bland Altman plots) to evaluate the reliability of the two activity monitors.

Results:
Compared to the ActiGraph GT3X+ as the standard, the Fitbit appears to be of limited value in terms of calorie quantification expended per day, times awake per night, and sleep efficiency percentage. While the Fitbit is of practical use and was considered to be more acceptable for use by the participants it has limited utility for reliably capturing research data on energy expenditure, the number of night time awakenings, and sleep efficiency percentage.

Conclusion:
The Fit bit shows the potential for reliable use in research studies whose outcome is based on physical activity measurements such as number of steps walked. Studies with a primary outcome of sleep quality may find limitations in this device.