DOI: 10.1249/tjx.0000000000000405 ISSN: 2379-2868

Accuracy of the Garmin Forerunner 55® for Estimating Maximal Oxygen Uptake in Male Recreational Runners: A Pilot Study

Rhennan Rodrigues Barbosa, Raphael José Perrier-Melo, Tuanny Nicolly Guimarães Silva, Guilherme Assunção Ferreira, Manoel da Cunha Costa
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Purpose:

This study aimed to evaluate the agreement between maximal oxygen uptake ( ) values measured during a maximal incremental treadmill test and those estimated by the Garmin Forerunner 55® smartwatch in trained male recreational runners.

Methods:

This cross-sectional observational study included 11 male recreational runners (38.2 ± 7.4 yr; 50.8 ± 5.5 mL·kg −1 ·min −1 , ; 22.8 ± 4.7% body fat; 22.5 ± 7.3 km weekly running volume). Each participant performed a maximal incremental treadmill test to determine using a metabolic gas analyzer. Estimated values were retrieved directly from the Garmin Connect® platform and corresponded to the most recent estimate generated by the Garmin Forerunner 55® before the laboratory assessment.

Results:

The Garmin Forerunner 55® systematically underestimated compared with laboratory measurements obtained during the graded treadmill test, with a mean difference of −1.96 ± 1.54 mL·kg −1 ·min −1 (95% confidence interval [CI]: −2.99 to −0.92; t = 4.207, P = 0.0018). This difference was associated with a large effect size (Cohen d = 1.27; 95% CI: 0.45–2.06), indicating a substantial bias toward lower estimates by the smartwatch. Bland–Altman analysis confirmed this systematic underestimation, with 95% limits of agreement ranging from −4.97 to +1.07 mL·kg −1 ·min −1 . Despite this bias, reliability was good to excellent (intraclass correlation coefficient = 0.883; 95% CI: 0.640–0.967), and the mean absolute percentage error was low (mean absolute percentage error = 3.8% ± 2.4%). A very strong positive correlation was observed between smartwatch-derived and laboratory-measured values ( r = 0.976; 95% CI: 0.907–0.994; R 2 = 0.95; P = 0.001), indicating that, although absolute values were underestimated, the smartwatch closely tracked interindividual differences in aerobic fitness.

Conclusion:

The Garmin Forerunner 55® systematically underestimated compared with laboratory measurements in male recreational runners. Nevertheless, its good reliability, low relative error, and strong association with laboratory-derived values suggest that it may be useful for tracking aerobic fitness, although caution is warranted when interpreting absolute individual estimates.

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