Study: 62 Garmin Devices Failed Clinical ECG HRV Accuracy Test

A new validation study comparing Garmin's HRV tracking against a clinical ECG standard found poor accuracy across 62 devices tested during real-world, full-day wear. This isn't a minor calibration issue. It puts serious doubt on the HRV data millions of athletes use daily to make training decisions.

The root cause isn't specific to Garmin. Optical heart rate sensors, the PPG technology sitting under nearly every wrist-based wearable, struggle to capture the millisecond-level beat-to-beat intervals that accurate HRV calculation requires. Garmin, Polar, Apple Watch, Coros, and Whoop all rely on variations of this same hardware approach. The ECG chest-strap standard these devices were measured against operates at a completely different level of signal precision.

For endurance athletes, this matters practically. HRV is the backbone of readiness scoring on platforms like Garmin's Body Battery, Whoop's Recovery score, and Polar's Nightly Recharge. If the raw HRV numbers feeding those algorithms are off, the training recommendations built on top of them are compromised. Telling yourself to take a rest day based on a 48ms RMSSD reading that could realistically be 39ms or 57ms is a problem.

The study does reflect what sports scientists have flagged for years: wrist-based HRV is best treated as a trend tool, not an absolute measurement. Comparing your own numbers week over week in consistent conditions, like Garmin's overnight HRV Status feature, holds more value than trusting a single morning reading. A chest strap like the Polar H10 paired with an HRV app remains the gold standard for athletes who want clinical-grade data.

Bottom line: don't bin your Garmin. But stop treating its HRV numbers like lab results. Trend tracking, consistent timing, and pairing with subjective feel still gives you a useful signal. Just know the margin of error is wider than the marketing suggests.