Wearable technology has become increasingly prevalent in monitoring health metrics, particularly in the context of cardiovascular care. This study, published in JMIR Cardio, evaluates 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 primary objective of the study was to compare the sedentary time recorded by the Fitbit Inspire 3 against a research-grade waist-worn accelerometer, the ActiveStyle Pro HJA-750C, which served as the gold standard. The study included 51 outpatients, with a mean age of 78.4 years, who wore both devices simultaneously for seven consecutive days.
Sedentary time was assessed during a standardized 12-hour daytime window, from 9 AM to 9 PM, at one-minute intervals. The researchers employed various statistical methods, including Pearson correlation, Bland-Altman analysis, and Lin concordance correlation coefficient (CCC), to evaluate the agreement between the two devices.
Key Findings
The results indicated that the Fitbit overestimated sedentary time by approximately 62 minutes compared to the waist-worn accelerometer. The correlation between the two devices was strong (r=0.905), and after applying a constant bias correction, the concordance improved significantly (CCC=0.904). Despite this improvement, the limits of agreement were wide, ranging from -11.3 to 135.2 minutes, indicating variability in individual measurements.
Furthermore, the study found that no demographic or clinical factors, such as sex, age, or diagnosis, significantly influenced the bias in measurements. The agreement in tertile classification was moderate, suggesting that while the devices may align well on average, individual-level precision remains constrained.
Implications for Use
The findings support the calibrated use of consumer-grade wearables like the Fitbit for monitoring sedentary behavior in a clinical setting, particularly for older patients with cardiovascular conditions. However, the authors caution that the population-specific correction factor requires further validation before being applied in different settings or populations.
What this study does not show
This study does not demonstrate that the Fitbit Inspire 3 can accurately measure sedentary behavior at an individual level without bias correction, nor does it establish the effectiveness of using such devices for clinical decision-making.
Evidence scorecard
- Analytic validity: Established
- Clinical validity: Partial
- Clinical utility: Not established
The evidence is based on a validation study involving human participants.