Garmin Fénix 7® underestimates performance at the lactate threshold in comparison to standardized blood lactate field test

Introduction & Purpose Lactate threshold (LT) is a critical performance measure traditionally obtained using costly laboratory-based tests. Wearables offer a practical and noninvasive alternative for LT assessment in recreational and professional athletes. However, the comparability of these estimates with the gold standards requires further evaluation. This study therefore aimed to compare pace and heart rate (HR) at the LT between the Garmin Fenix 7® threshold running test and a standardized blood lactate field test. Methods In our sample of 26 participants (nf = 7 and nm = 19; 25.97 (± 6.26) years, BMI: 24.58 (± 2.8) kg/m2) we determined running pace and HR at LT with two subsequent tests. First, all participants were equipped with a Fenix 7® smartwatch for a calibration phase of 5 weeks. Subsequently, all performed the Fenix 7® threshold running test, which guides the athlete through incrementing HR zones. Based on that, the watch estimated pace and HR at LT. After a break of at least 48 h, they were tested in a standardized, graded blood lactate field test analyzed by the modified D-Max method (Cheng et al, 1992). Results Pace at LT calculated by Fenix 7® (M =11.87 km/h ± 1.26 km/h) was 11,8% lower compared to the field test (M =13.28 km/h ± 1.72 km/h), which was significant (p < .001, d = -1.19). HR estimated by the watch at LT was 1,72% lower (p > .05). LT data obtained in the field test showed greater overall variance. Conclusion Our results suggest sufficient accuracy of Fenix 7® LT estimates for recreational athletes. It can be assumed that for professional athletes, it would fail to provide the nuanced data needed for high-quality training management. References Cheng, B., Kuipers, H., Snyder, A., Keizer, H., Jeukendrup, A., & Hesselink, M. (1992). A new approach for the determination of ventilatory and lactate thresholds. International Journal of Sports Medicine, 13(7), 518–522. https://doi.org/10.1055/s-2007-1021309