Correlation between Fitbit active zone minutes and CPET-derived ventilatory thresholds in telecardiac rehabilitation patients

Background Cardiac rehabilitation (CR) is key in preventing cardiovascular disease (CVD) but adherence to center-based CR and continued physical activity in phase III remains low. Telecardiac rehabilitation (teleCR) offers a cost-effective alternative, enabling remote monitoring and promoting physical activity with wearable trackers that measure daily step counts. Increasing daily steps is linked to reduced CVD risk, with 10,000 steps seen as an ideal target. However, reaching this goal can be difficult for those with sedentary jobs. Recent studies show that higher exercise intensity can lead to greater risk reduction in less time, emphasizing the importance of monitoring exercise intensity. Fitbit devices categorize heart rate into fat burn, cardio, and peak zones, but these estimations have not been validated in cardiac patients, especially those on beta-blockers. Purpose This study aims to evaluate the correlation between Fitbit-derived active zone minutes and cardiopulmonary exercise testing (CPET)-derived ventilatory thresholds (VT) in patients following teleCR to assess their clinical applicability. Methods A prospective study was conducted at Jessa Hospital Rehabilitation and Health Centre (ReGo). Patients that accepted the teleCR program received a fitbit smartwatch and were included. Baseline characteristics and CPET-derived heart rate zones, were collected using the electronic medical records and Fitbit-derived heart zones were collected from the patient’s smartphone. Results On average, Fitbit-estimated heart rates were 17 bpm higher than CPET-measured HRmax. This discrepancy was significantly more pronounced in patients on beta-blockers (+22 bpm, p < 0.001), while in patients not taking beta-blockers, the difference was not significant (+3 bpm, p = 0.68). Overestimation occurred in 88% of beta-blocker users and 43% of non-users. Similar trends were observed when comparing Fitbit heart rate values for fat burn and cardio zone to CPET-derived VT1 and VT2 respectively, although to a lesser extent. In contrast, for patients not on beta-blockers, Fitbit heart rate estimates tended to be underestimated, yet approximately one-third still presented overestimations. Conclusion These findings indicate that Fitbit active zone minutes are not a reliable tool for monitoring exercise intensity in teleCR patients, particularly for those on beta-blockers. Ideally, personalized intensity zones should be manually adjustable to reflect true physiological values, enhancing the clinical utility of wearable activity trackers in cardiac rehabilitation.