What should you know about wrist heart rate
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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. The wrist heart rate technology in Suunto watches is provided by Valencell Inc.

The accuracy of wrist heart rate measurement is influenced by a number of factors and can be affected by individual differences between people. Therefore, wrist heart rate measurement should be considered an estimate.

How to wear your Suunto wrist heart rate watch - a better fit for better readings 

One of the factors with the biggest impact is, how you wear your watch. The right fit can help improve the accuracy of your heart rate readings. Start with the following tips, and then test and improve the fit of your watch until you find your personal sweet spot. 


During daily use
Wear your Suunto watch at least 1 finger above your wrist bone and make sure the watch is snug on your wrist. Your watch should always maintain a contact with your skin, so that you can't see the light shining from the sensor.
During exercise
Test the fit – the key is to wear the watch as high up on your wrist as possible, and to prevent it from sliding down during exercise. A good indicator is to wear it about 2 fingers above your wrist bone. Again, make sure you wear the watch tight and evenly against the skin, however not too tight to cut off blood circulation.


Too loose Just right


Keep in mind when wearing a wrist heart rate watch

For best possible results: 

  • Warm-up to get your heart rate up before starting your exercise. This ensures your watch provides stable readings from the start.
  • If your watch loses your heart rate during exercise, pause for a moment (approximately 10 – 30 seconds). Continue once your watch is locked onto your heart rate.

Try to avoid:

  • Wearing the watch too loose. Make sure the sensor is always in direct contact with your skin, you shouldn't be able to see the light shining from the sensor.
  • Wearing the watch too tight. Wearing the watch extremely tight can cut off blood flow and reduces the sensor's ability to monitor heart rate.

How optical heart rate measurement works

In practice, the optical heart rate sensor on the underside of the watch shines light into your wrist using LEDs and measures 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). 

Good to know about wrist heart rate measurement 

Wrist heart rate measurement is an easy and convenient way to track your heart rate. However, please keep in mind that the accuracy and reliability of optical heart rate measurement varies from person to person and may not work at all with certain types of activities. Currently, the best wrist heart rate measurements stay 90% of the time within 5% of the chest-measured heart rate.

Together with Valencell, we identified the following factors that may affect heart rate measurement:

  • When exercising in cool or cold temperatures, your body attempts to keep your body temperature stable by directing the blood flow from arms and legs towards the core of your body. This reduction in blood flow to the arms can make it more difficult for the sensor to measure heart rate accurately.
  • If you frequently have cold hands, a proper warmup before exercising may be needed to improve the accuracy of heart rate reading.
  • Arm movements and flexing muscles, such as gripping a tennis racket or doing Crossfit style high-intensity training, can change the accuracy of the sensor readings.
  • The optical sensor may not provide accurate heart rate readings for swimming activities, as water passing under the watch affects the optical sensor's ability to read heart rate accurately.
  • Dark tattoos can prevent reliable readings from the optical sensor.

If you continue to have issues with wrist based OHR, 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.

Always remember that heart rate readings, optical or otherwise, are estimates and only for reference and recreational use and not intended for medical use of any kind.