How Heart Rate Monitors Work — Which One to Choose for Cycling
A heart rate monitor is the cheapest way to objectively measure training intensity. Before you spend several hundred dollars on a power meter, put a fraction of that into a heart rate sensor — it gives you more usable information than a speedometer ever will.
How heart rate monitors work
Chest strap sensor
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 1–2 beats. The standard for cycling training.
Wrist sensor (optical)
LEDs illuminate the skin and a photodiode measures changes in blood flow. Convenient (built into the watch), but less accurate — wrist movement, sweat, and muscle contraction distort the reading. During intervals, lag can be 10–15 seconds.
Armband sensor (optical)
A compromise — a bicep band combines the convenience of no chest strap with better accuracy than a wrist sensor (less movement, thicker blood vessels).
Chest strap vs. wrist — which to choose?
| Criterion | Chest strap | Wrist |
|---|---|---|
| Accuracy | Very high | Good at steady pace, weak during intervals |
| Comfort | The strap can be annoying | Built into the watch — no extra hardware |
| Lag | 1–2 s | 5–15 s |
| Price | Low, one-time purchase | Included in watch price |
| Connectivity | ANT+ and/or Bluetooth | Bluetooth (via watch) |
For cycling training, a chest strap is the better call — you're seated and relatively still, so the strap doesn't get in the way, and accuracy matters most when you're steering intervals off of it.
What to look for when buying
- Dual-band (ANT+ and Bluetooth) — pairs with both a bike computer and a phone or watch.
- Battery swap vs. rechargeable — coin-cell straps last 6–12 months; rechargeable ones run 20–40 hours.
- Strap comfort — soft, elastic material with adjustment. It should sit snug, not pinch.
How to use heart rate data
A raw HR number tells you little on its own. The value comes from knowing 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 changes in effort and shifts with stress, temperature, and caffeine. If you want more precise data, the next step up is a power meter.
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