Why Heart Rate Monitoring Matters
Training by heart rate is one of the most effective ways to ensure you're working at the right intensity — hard enough to drive adaptation, easy enough to actually recover. But the accuracy of your data depends heavily on the type of monitor you're using and how you're using it.
There are two main technologies: chest straps (electrocardiography-based) and optical sensors (photoplethysmography-based, found in wrist watches and arm bands). Both measure heart rate, but they do it differently — and the differences matter depending on your sport, training style, and how much you care about data precision.
How Each Technology Works
Chest Straps
Chest straps use electrodes pressed against the skin to detect the electrical signals produced by each heartbeat — the same principle as an ECG. The signal is clean, direct, and highly accurate because it's measuring the electrical event itself, not a downstream effect of it.
Optical Sensors
Optical sensors use LEDs to shine light into the skin and measure changes in blood volume as the heart pumps — a technique called photoplethysmography (PPG). Wrist-based sensors in GPS watches use this method, as do dedicated optical arm bands. The technology has improved significantly, but it remains more susceptible to motion artefact and skin contact issues than electrical measurement.
Accuracy: Where Each Technology Excels and Struggles
Chest Straps
- ✅ Highly accurate across all intensities and activities
- ✅ Responds instantly to changes in heart rate — no lag
- ✅ Reliable during interval training, sprints, and rapid HR changes
- ✅ Unaffected by motion, cold hands, or skin tone
- ❌ Less comfortable for some athletes, particularly in cold or wet conditions
- ❌ Requires a compatible device to display data
Optical (Wrist or Arm Band)
- ✅ Convenient — no additional hardware if using a GPS watch
- ✅ Accurate during steady-state efforts (easy runs, long rides at consistent pace)
- ✅ Comfortable for all-day wear and sleep tracking
- ❌ Lags behind actual heart rate during rapid intensity changes
- ❌ Less accurate during high-cadence cycling, rowing, or activities with significant wrist movement
- ❌ Can be affected by cold temperatures, tattoos, and poor skin contact
The honest summary: For steady-state training and general fitness monitoring, optical is good enough. For interval training, threshold work, racing, or any situation where precise, real-time heart rate data matters, a chest strap is meaningfully more accurate.
Which Should You Use?
Use a chest strap if you:
- Train with structured intervals or use heart rate zones precisely
- Race and want accurate data during high-intensity efforts
- Cycle at high cadence (wrist optical struggles here)
- Use heart rate variability (HRV) data for recovery monitoring
- Want the most accurate data possible, full stop
Use an optical sensor if you:
- Primarily do steady-state training (easy runs, long aerobic rides)
- Want all-day heart rate monitoring without wearing a strap
- Prefer minimal kit and convenience over maximum precision
- Are new to heart rate training and want to start simply
Use both if you:
- Want chest strap accuracy during training but optical convenience for daily monitoring and sleep
- Are a triathlete who needs reliable data across swim, bike, and run
The Products
Chest Straps
Optical Sensors
GPS Watches with Wrist-Based Optical HRM
All of the GPS watches in our range include wrist-based optical heart rate monitoring as standard. For athletes who want to pair a chest strap with a watch for training accuracy while retaining optical for daily monitoring:
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Polar Vantage V3 — Polar's flagship, with the most advanced wrist optical sensor in the range and full H10 chest strap compatibility -
Coros Pace 4 — Pairs with the Coros HRM arm band for improved accuracy during cycling -
Suunto Race — Pairs natively with the Suunto Smart Heart Rate Belt
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HRV Monitoring: A Note on Chest Strap Advantage
Heart rate variability (HRV) — the variation in time between heartbeats — is increasingly used by athletes to assess recovery readiness. HRV measurement requires beat-to-beat accuracy that optical sensors, particularly wrist-based ones, cannot reliably deliver.
If HRV monitoring is part of your training approach, a chest strap like the Polar H10 is essential for accurate morning readings. Wrist optical HRV data should be treated as directional rather than precise.
Key Takeaways
- Chest straps are more accurate, especially during intervals, high-intensity efforts, and HRV monitoring
- Optical sensors are more convenient and accurate enough for steady-state training and daily monitoring
- Arm-band optical (Polar Verity Sense, Coros HRM) bridges the gap — better than wrist optical, more comfortable than a chest strap
- For most serious athletes, the ideal setup is a chest strap for training and wrist optical for daily wear
- The Polar H10 is the benchmark chest strap; the Polar Verity Sense is the benchmark optical arm band
