How Accurate Are Wrist-Worn Heart Rate Monitors?

Heart rate monitors have become indispensable tools for runners and fitness enthusiasts. Most smartwatches and fitness bands use wrist-based optical sensors, known as photoplethysmography (PPG). Here is what the research tells us about their accuracy.

What the Research Found

• At rest — for people in normal (sinus) rhythm: average error of around 4.6 bpm. For those in AF: average error of 7.0 bpm.
• During intense exercise — in sinus rhythm: average error soared to 13.8 bpm. In AF: error ballooned to 28.7 bpm.

These discrepancies were both statistically significant and large enough to matter if you're training by heart rate zones.

What This Means for Runners

At Rest or Easy Runs

Wrist-based monitors generally offer acceptable accuracy for daily tracking and recovery. They're comfortable and convenient — great for monitoring resting heart rate or light activity.

During High-Intensity Efforts

Accuracy drops sharply. For runners using heart rate zones during workouts (e.g., tempo runs, intervals), wrist sensors might misguide your effort.

Wrist-Based vs Chest Strap Monitors

Wrist monitors (PPG) use green LED lights that shine into your skin, detecting changes in blood flow. They work well at rest and during steady, low-intensity exercise. Limitations: motion, sweat, or skin tone can interfere with accuracy, and they often struggle during high-intensity workouts.

Chest strap monitors (ECG) measure heart rate using electrical signals — the same principle as a hospital ECG. These are the gold standard for accuracy, reliable across all intensities and conditions. The limitation is comfort.

Which One Should You Use?

• Everyday runners: A wrist-based monitor is usually "good enough" for general training and lifestyle tracking.
• Performance-focused runners: A chest strap ensures reliable data during intervals, races, and training sessions where precision matters.
• Best of both worlds: Many athletes wear a wrist monitor for convenience but switch to a chest strap for key workouts.