Wrist HRM is fine for easy training. For race-day pacing decisions, you need a chest strap or optical armband. The five below are the ones we'd actually wear, ranked.
The picks
Polar
Polar H10 Heart Rate Sensor
The benchmark chest strap. Most accurate consumer HR sensor on the market, period. ECG-quality signal, dual ANT+/Bluetooth, used by every major coaching service.
- ECG-quality accuracy
- ANT+ + Bluetooth dual broadcast
- 400-hour battery (replaceable)
- Works with Garmin, COROS, Apple Watch, Wahoo
Garmin
Garmin HRM-Pro Plus
Adds running dynamics and pace/distance data when GPS drops out. The right pick if you live in the Garmin ecosystem; richer data than Polar at the cost of $40.
- Running dynamics + cadence
- GPS-backup distance/pace
- ANT+ + Bluetooth
- Stores HR data offline (pool/gym)
COROS
COROS HRM Heart Rate Monitor (Armband)
Optical sensor in an armband — comfortable for hours of running where chest straps chafe. Newer 5-LED design measures with chest-strap accuracy on most skin types.
- 5-LED optical array
- No chafe on long runs
- ANT+ + Bluetooth
- 38-hour battery, USB rechargeable
Wahoo
Wahoo TICKR X HRM
50 hours of onboard memory — the right strap if you want to swim or train without a watch. Captures cadence, indoor speed, and running smoothness scores.
- 50 hr onboard memory
- Running cadence + smoothness metrics
- ANT+ + Bluetooth
- Long battery (replaceable)
Polar
Polar Verity Sense Optical Armband
Wear it on the bicep, the forearm, the temple. Pool-rated. 600 hr offline storage. The HRM that goes everywhere — yoga, swim, sauna heat-acclim sessions.
- Wear anywhere — bicep, forearm, temple
- Pool-rated (waterproof)
- 600-hour offline memory
- ANT+ + Bluetooth + memory mode
Chest strap vs optical armband
Chest straps measure ECG (electrical heart signal) — the same signal a hospital uses. Optical sensors measure blood-volume changes through skin (photoplethysmography). Chest is more accurate; optical is more comfortable.
For a 100-mile race, chest-strap chafing becomes a real issue. Most ultrarunners switch to an optical armband (COROS or Polar Verity Sense) for ultras and use a chest strap for training. The 1–2% accuracy loss isn't material at race pace.
Why wrist HRM falls apart at race pace
Wrist optical sensors struggle with three things ultrarunners do constantly: cold weather, hand-pumped poles, and water immersion. Cold = vasoconstriction = reduced signal. Pole work = motion artifact. Aid station hand-washing = reset. Wrist HRM is fine for easy training, often wrong for race-day decisions.