How a Heart Rate Monitor Works and Which One to Choose for Cycling
A heart rate monitor is the cheapest way to objectively measure training intensity. Before spending on a power meter, a few dozen euros on a chest strap gives you more usable data than speed alone.
How does a heart rate monitor work?
Chest strap
Measures the heart's electrical signal (like a simplified ECG) through electrodes in the strap. The most accurate method — deviation from a clinical ECG is typically 1–2 beats. The standard in structured cycling training.
Wrist-based (optical)
LEDs illuminate the skin and a photodiode reads changes in blood flow. Convenient (built into a watch) but less accurate — wrist movement, sweat, and muscle contraction disrupt the reading. During intervals, lag can run 10–15 seconds.
Arm band (optical)
A compromise — a bicep strap combines convenience (no chest strap) with better accuracy than the wrist (less movement, thicker vessels).
Chest vs. wrist — which should I choose for cycling?
For cycling training, a chest strap is the better choice — you're sitting relatively still, so the strap isn't a hindrance, and accuracy matters most when steering intervals off heart rate.
| Criterion | Chest | Wrist |
|---|---|---|
| Accuracy | Very high | Good at steady pace, weak during intervals |
| Comfort | Strap can bother some riders | Built into your watch, no extra gear |
| Lag | 1–2 s | 5–15 s |
| Price | €25–70 | Included in watch price |
| Connectivity | ANT+ and/or Bluetooth | Bluetooth (via watch) |
What to check before buying
- Dual-band (ANT+ and Bluetooth) — connects to both a bike computer and a phone or watch.
- Battery replacement vs. rechargeable — CR2032 straps last 6–12 months; rechargeable straps last 20–40 hours.
- Strap comfort — soft, elastic material with adjustment. It should sit snug without pinching.
How to use heart rate data
A raw HR reading alone doesn't tell you much. It becomes useful once you know your heart rate zones:
- Zone 1 (50–60% HRmax) — recovery
- Zone 2 (60–70% HRmax) — aerobic base
- Zone 3 (70–80% HRmax) — tempo / endurance
- Zone 4 (80–90% HRmax) — lactate threshold
- Zone 5 (90–100% HRmax) — VO2max
A heart rate monitor is a great starting point, but it has limits: heart rate lags behind effort changes and shifts with stress, temperature, and caffeine. If you want more precise data, the next step is a power meter.
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