Are Activity Wrist-Worn Devices Accurate for Determining Heart Rate during Intense Exercise?
Level 4 - case-series / case-control
Small cross-sectional validation study comparing consumer devices to a reference standard
OpenAlex W4320917308 · doi:10.3390/bioengineering10020254
What was done
Eight athletes underwent maximal exercise stress testing on a cycle ergometer or a treadmill while wearing four wrist-worn devices (Fitbit Charge, Apple Watch, Tomtom runner Cardio, and Samsung G2). Heart rate recordings were compared against continuous electrocardiogram (ECG) data across 1,286 simultaneous data pairs.
What was found
The abstract reports no numerical accuracy metrics or error rates. All four devices were reasonably accurate at baseline activity levels. At higher exercise intensities (above 150 bpm), the Fitbit Charge and Samsung G2 underestimated heart rate, while the Apple Watch and Tomtom runner Cardio remained fairly reliable.
Why it matters
Optical heart rate accuracy in consumer wearables can degrade substantially under high-intensity physical exertion, meaning certain models are unreliable for tracking peak cardiovascular training or high-intensity exercise.
Limits
The sample size is very small (n = 8 athletes). The abstract reports no quantitative statistical metrics (e.g., mean absolute percentage error, Bland-Altman limits of agreement) and omits participant demographic characteristics such as sex or skin tone that can influence optical sensor accuracy.
Cited by
- supports Smartwatches and wrist-based heart rate sensors tend to become less accurate as exercise intensity increases.