Wearable technology has become increasingly prevalent in monitoring health metrics, particularly in the context of cardiovascular care. This validation study, published in JMIR Cardio, aimed to evaluate the accuracy of a consumer-grade wrist-worn activity tracker, specifically the Fitbit Inspire 3, in measuring sedentary behavior among older outpatients with cardiovascular disease.
Study Overview
The study involved 51 outpatients diagnosed with heart failure or ischemic heart disease, who wore both the Fitbit Inspire 3 and a research-grade waist-worn accelerometer (ActiveStyle Pro HJA-750C) simultaneously for a week. The primary focus was to assess the agreement between the sedentary time reported by the Fitbit and the research-grade device under free-living conditions.
Key Findings
Results indicated that the mean sedentary time recorded by the waist-worn accelerometer was approximately 498 minutes, while the Fitbit reported a higher mean of about 560 minutes. The correlation between the two devices was strong (r=0.905), suggesting that while the Fitbit can track sedentary behavior effectively, it tends to overestimate sedentary time by about 62 minutes on average.
Further analysis showed that the Fitbit had a fixed bias but no proportional bias, meaning that the overestimation was consistent across different levels of sedentary behavior. After applying a correction for the fixed bias, the concordance between the two devices improved significantly, indicating that with calibration, consumer-grade trackers can be reliable for monitoring sedentary behavior in this population.
Implications for Use
The findings support the calibrated use of consumer wearables like the Fitbit in outpatient cardiac care, allowing for scalable monitoring of sedentary behavior. However, the study also highlighted the wide limits of agreement, which may affect individual-level accuracy. Thus, while the device can be useful for group-level assessments, individual results should be interpreted with caution.
What this study does not show
This study does not establish the Fitbit’s accuracy for individual-level sedentary behavior measurement without applying a correction factor, nor does it validate its use in populations outside of the studied cohort.
Evidence scorecard
- Analytic validity: established
- Clinical validity: partial
- Clinical utility: partial
The evidence class for this study is primary_research, focusing on human participants.