Garmin Fénix 7^® Underestimates Performance at the Lactate Threshold in Comparison to Standardized Blood Lactate Field...

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 regular field tests requires further evaluation.

In our sample of 26 participants (n_f=7 and n_m=19), we compared the estimated running pace and heart rate (HR) at LT with two subsequent tests. First, participants performed the Fenix 7^® threshold running test after a calibration phase. Subsequently, they were tested in a standardized, graded blood lactate field test. Age was 25.97 (± 6.26) years, and body mass index (BMI) was 24.58 (± 2.8) kg/m².

Pace at LT calculated by Fenix 7^® (M=11.87 km/h ± 1.26 km/h) was 11.96% lower compared to the field test (M=13.28 km/h ± 1.72 km/h), which was significant (p <0.001, d=-1.19). HR estimated by the Fenix 7^® at LT was 1.71% lower (p >0.05). LT data obtained in the field test showed greater overall variance.

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.