BACKGROUND: Many runners have adopted Garmin watches to monitor their exercise training loads, estimate VO2max, and analyze recovery data. However, the accuracy of wrist-based fitness trackers and the reliability of the VO2max estimates has been mixed. While technology continues to greatly improve the quality of the data from these devices, no studies have empirically tested the accuracy of the new Garmin Forerunner 265. Accordingly, we determined the accuracy of VO2max measurements from the Garmin Forerunner 265 compared to values obtained in our applied physiology laboratory. METHODS: Six subjects (average age 28.5 ± 6.9 years) wore the Garmin Forerunner 265 on the wrist of their non-dominant arm while completing a mapped, 10-minute outdoor run. The Garmin-estimated VO2max (ml/kg/min) obtained after this run was then compared against oxygen consumption data obtained following a standard, graded exercise test using a Woodway treadmill and Parvo metabolic cart . Mean absolute percentage error (MAPE), percent change, and dependent samples t-test were used to compare values. Significance was accepted at p ≤ 0.05. RESULTS: We determined that VO2max was achieved during the graded exercise test due to several criterion, including a high rate of perceived exertion (19.5 ± 0.5), heart rate within 10 bpm of predicted max (190.2 ± 15.7), an RER over 1.1 (1.13 ± 0.06), and a plateau in oxygen consumption. Average VO2max estimates following this challenge were 46.1 ± 7.41 ml/kg/min and were not significantly different (p = 0.15) than estimates from the Garmin Forerunner 265 (51.3 ± 3.6 ml/kg/min). Together, the average percent change (13.3 ± 15.5%) and relatively high MAPE (18.4 ± 8.6%) suggest that Garmin may overestimate oxygen consumption compared to values acquired in the laboratory. CONCLUSION: The Garmin Forerunner 265 should be used with caution when designing or adjusting training programs based on oxygen consumption data, particularly as the MAPE is greater than 10%. Future studies should investigate if extended, continual use of the Garmin Forerunner 265 would normalize VO2max estimates and make them comparable to values obtained using gold-standard equipment in a controlled laboratory setting.

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