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What should you know about wrist heart rate?

In a nutshell, wrist heart rate technology measures heart rate via LEDs that track blood flow in your wrist. This means that you can see your heart rate data during a specific activity or in daily use without a chest heart rate strap. 

Deep-dive into wrist heart rate measurement

Suunto wrist heart rate watchesHow does the wrist heart rate work?
Suunto Spartan Wrist HR watches use optical heart rate monitoring technology created by Valencell, the leading innovator in wearable biometric data sensor technology.

In practice, the optical heart rate sensor on the underside of the watch shines light into user's wrist using LEDs and measures the amount of light that is scattered by blood flow. This is based on the fact that light entering the body will scatter in a predictable manner when the blood flow dynamics change, such as with changes in blood pulse rate or with changes in blood volume (cardiac output).

What are the benefits of wrist heart rate measurement?
The benefit of wrist heart rate is the convenience – the possibility to measure heart rate without having to wear a separate heart rate belt or other sensor.

Is wrist heart rate accurate and reliable?
Wrist heart rate technology has developed with great steps over the past few years, although it's not quite reaching the accuracy of heart rate measured with a chest strap like Suunto Smart Sensor. Currently, the best wrist measurements stay 90% of the time within 5% of the chest-measured heart rate.

Optical heart rate measurement is sensitive to the movement of the watch and thus it's important to tighten the watch properly and wear it slightly higher up on the arm compared to a regular watch. The measurement also tends to have individual variance depending on user's surface blood circulation properties.

What should I consider when using wrist heart rate measurement?
Wrist-based heart rate measurement is at its best in activities that enable the watch to consistently read HR data from user's arm, i.e. when blood flow is steady, and when the watch itself is constantly in touch with skin. Activities like this include running, biking, and day-to-day lifestyle activities (including measuring resting heart rate).

On the other hand, in activities that involve irregular arm motion and vary much in their intensity, such as high-intensity interval strength training, Crossfit or racket sports, the device may become less accurate. This is due to the fast and uneven blood flow and the hand movements which make it harder for the optical sensor to get a good reading. However, the watch will return to its normal level of accuracy during resting periods.

Swimming is tough on wrist heart rate measurement too, as water passing under the watch affects the optical sensor's ability to read heart rate accurately.

 Suunto Spartan Sport Wrist HR lineup

How to ensure the best possible performance of wrist heart rate?

Wrist heart rate measurement is an easy and convenient way to track your heart rate. To get the best results, it's important to keep in mind factors that may affect heart rate measurement:

  • The watch must be worn directly against your skin. No clothing, however thin, can be between the sensor and your skin.
  • The watch may need to be higher on your arm than where watches are normally worn. The sensor reads blood flow through tissue. The more tissue it can read, the better.
  • Arm movements and flexing muscles, such as gripping a tennis racket, can change the accuracy of the sensor readings.
  • When your heart rate is very low, the sensor may not be able to provide stable readings. A short warm up of a few minutes before you start the recording helps.
  • The optical sensor may not provide accurate heart rate readings for swimming activities.
  • Darker skin pigmentation and tattoos can block light and prevent reliable readings from the optical sensor.
  • For highest accuracy and quickest responses to changes in your heart rate, we recommend using a compatible chest heart rate sensor such as Suunto Smart Sensor. Using a heart rate belt will enable getting heart rate readings also when mounting the watch on the handlebar of a bike or wearing it on top of a sleeve.