# Validity of V̇O2max estimates from the forerunner 245 smartwatch in highly vs. moderately trained endurance athletes

## TL;DR

This study compares a smartwatch's estimate of maximum oxygen uptake (V̇O₂max) with lab results in endurance athletes, finding it less accurate for highly trained individuals.

## Contribution

The study reveals that smartwatch V̇O₂max estimates are less valid for highly trained athletes compared to moderately trained ones.

## Key findings

- Smartwatch underestimated V̇O₂max by 4.73 and 4.05 ml·min⁻¹·kg⁻¹ in two runs.
- Moderately trained athletes had lower errors (MAPE: 4.1–2.8%) compared to highly trained ones (MAPE: 10.4–9.4%).
- Laboratory gas analysis is more accurate for highly trained individuals.

## Abstract

Assessing the validity of maximum oxygen uptake (V̇O₂max) estimates provided by a commercially available smartwatch (Garmin Forerunner 245, Garmin Ltd., Olathe, USA) compared to laboratory-based respiratory gas analysis in moderately-to-highly trained athletes.

Thirty-five endurance athletes (Tier 2–3 athletes, 24 males, 11 females; age: 25.1 ± 3.5 years; V̇O₂max: 60.1 ± 8.2 ml·min⁻1·kg⁻1) completed a treadmill ramp test with respiratory gas analysis to determine criterion V̇O₂max. Additionally, each athlete performed two submaximal 15-min outdoor runs at > 70% of maximum heart rate, during which the smartwatch estimated V̇O₂max. Athletes were stratified into moderately trained (V̇O₂max ≤ 59.8 ml·min⁻1·kg⁻1) and highly trained (V̇O₂max > 59.8 ml·min⁻1·kg⁻1) subgroups.

Across all athletes, the smartwatch underestimated V̇O₂max [mean differences: − 4.73 ml·min⁻1·kg⁻1 (run 1), -4.05 ml·min⁻1·kg⁻1 (run 2)]. Intraclass correlation coefficients (ICC) indicated moderate agreement between smartwatch and laboratory values (run 1: ICC = 0.71 [95% CI: 0.03–0.90]; run 2: ICC = 0.75 [95% CI: 0.17–0.91]), with mean absolute percentage errors (MAPE) of 7.9% and 7.2%. Subgroup analyses revealed better accuracy of smartwatch estimated V̇O₂max in moderately trained group (MAPE: 4.1–2.8%; ICC: 0.63–0.66 [95% CI: 0.09–0.87]), whereas in highly trained athletes, the smartwatch underestimated V̇O₂max by 6.3 ml·min⁻1·kg⁻1 (MAPE: 10.4–9.4%; ICC: 0.34–0.41 [95% CI: − 0.11–0.75]).

Smartwatch-derived V̇O₂max estimates are valid in moderately trained athletes but less valid in highly trained individuals. While smartwatches are useful for general monitoring, caution is warranted in their interpretation, particularly in highly trained individuals. Laboratory-based gas analysis remains the preferred method when precision is required.