In recent years, wearable technology has become increasingly prevalent in monitoring health metrics, particularly in populations with specific health conditions such as cardiovascular disease. This validation study published in JMIR Cardio investigates the accuracy of a consumer-grade wrist-worn activity tracker, specifically the Fitbit Inspire 3, in measuring sedentary behavior among older Japanese outpatients with cardiac issues.
Study Overview
The study involved 51 outpatients, with a mean age of 78.4 years, who wore both the Fitbit Inspire 3 and a research-grade waist-worn accelerometer (ActiveStyle Pro HJA-750C) simultaneously for seven consecutive days. The aim was to assess the agreement in sedentary time measurement between these two devices during a standardized 12-hour daytime window (9 AM to 9 PM).
Key Findings
The results indicated that the mean sedentary time recorded by the waist-worn accelerometer was 497.9 minutes, while the Fitbit recorded a higher mean of 559.9 minutes. The strong correlation between the two devices was noted (r=0.905), suggesting that the Fitbit could be a reliable tool for measuring sedentary behavior, albeit with some caveats.
However, the Fitbit showed a significant fixed bias, overestimating sedentary time by approximately 62 minutes. This fixed bias was consistent across the study population, and while it did not exhibit proportional bias, the wide limits of agreement (-11.3 to 135.2 minutes) indicate variability in individual measurements.
After applying a constant correction for the bias, the concordance correlation coefficient improved significantly, indicating that with calibration, the Fitbit could provide more accurate group-level data. The study also highlighted that no demographic or clinical factors moderated the bias, suggesting a uniformity in the measurement error across different patient profiles.
Implications for Use
The findings support the calibrated use of consumer-grade wearables like the Fitbit Inspire 3 for monitoring sedentary behavior in outpatient cardiac care. However, the authors caution that the wide limits of agreement limit the precision of individual-level assessments. They also emphasize the need for independent validation of the population-specific correction factor before it can be applied to other settings.
What this study does not show
This study does not demonstrate that the Fitbit Inspire 3 is suitable for individual-level precision in measuring sedentary behavior without calibration, nor does it validate its use in populations outside the specific cohort studied.
Evidence scorecard
- Analytic validity: Established
- Clinical validity: Partial
- Clinical utility: Not established
The evidence class for this study is primary_research, focusing on human participants.