The what and how of Polar's wrist-based heart rate measurement

Wearing a device with the wrist-based heart rate measurement feature is the most convenient and easy way to measure your heart rate while you’re working out. You don’t have to wear a separate chest strap to track your heart rate because the wrist device reads your heart rate optically through the skin on your wrist. When you want to start tracking your heart rate, the only thing you need to do is tighten the wristband.

Polar devices that include the wrist-based heart rate measurement feature (M200, M430, Grit X, Grit X Pro, Grit X2 Pro, Ignite, Ignite 2, Ignite 3, Vantage M, Vantage M2, Vantage V, Vantage V2 and Vantage V3) also monitor everything that you do throughout the day and help you become aware of the level of your activity. They keep track of your activity, workouts, sleep, calories burned, and many other areas of your daily life, sync the data to your mobile phone, and give you personalized training guidance. Information about steps taken and calories burned can help you plan your routines and workouts better and motivate you to adjust your lifestyle to fit your goals.

The main difference is in how you wear the measuring devices. Traditional chest strap heart rate monitors are worn around the chest because they measure electric signals that the heart generates as it beats and pushes blood to circulation. With a chest strap heart rate monitor you usually need a separate wrist device or mobile to pick up the heart rate signals from the chest strap and to interpret the received data. Polar devices with wrist-based heart rate measurement can be worn alone without a chest strap. They are always ready when you are to track your heart rate from your wrist.

Certain factors, like sports with extreme arm motions (racket sports), wet conditions (swimming) and training in cold conditions (skiing), may affect the wrist based heart rate measurement. In these cases, the Polar H10 / H9 heart rate sensor is the optimal training companion. Polar H10 heart rate sensor is more responsive to rapidly increasing or decreasing heart rate, so it’s the ideal option also for interval type of training with quick sprints.

With the Polar H10 / H9 heart rate sensor, you can get detailed HRV (heart rate variability) based information about your body and fitness in case you’re looking for more personalized guidance for your training habits.

Polar devices that have the wrist-based heart rate measurement feature (M200, M430, Grit X, Grit X Pro, Grit X2 Pro, Ignite, Ignite 2, Ignite 3, Pacer, Pacer Pro, Vantage M, Vantage M2, Vantage V, Vantage V2 and Vantage V3) use a technology called optical heart rate monitoring (OHR). It's a technology that's been used in hospitals for some time already and is based on detecting your blood flow optically through the skin on your wrist.

On the back of your Polar device there are LEDs that shine a bright light through the skin on your wrist, and a photodiode that detects the intensity of the light reflecting back from the skin. Now, when your heart beats, it pumps blood to your arteries. When the blood flow is stronger in the arteries on your wrist, less light is reflected back to the photodiode. Between the heart beats, the blood flow is weaker in your wrist, and more light is reflected back to the photodiode. From these variations in the intensity of the light reflecting back from your skin, the Polar devices with wrist-based hear rate measurement can determine your heart rate.

Optical heart rate monitoring is very sensitive to motion. Movement can interfere with the LED light's route to the detector and with measuring the heart rate. To filter out distortions caused by movement, the Polar devices with wrist-based heart rate monitoring use two sensors: one to sense the heart rate, and one to sense the movement of the hand. The movement data is then run through an algorithm that combines information from both sensors to give you an accurate heart rate reading.

To be able to get reliable heart rate measurements from your wrist, make sure that you wear the Polar device correctly:

• Wear the Polar device on top of your wrist, at least a finger’s width up from the wrist bone (see the picture below).
• Tighten the wristband firmly around your wrist. The sensor on the back must be in constant touch with your skin and the Polar device should not be able to move on your arm. Movement between the wrist unit and your skin can interfere with the readings.
• A good way to check that the wristband is not too loose is if you push the wristband lightly up from both sides of your arm and make sure the sensor doesn’t lift from your skin. When pushing the wristband up you shouldn't see the LED light shining from the sensor.

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Activities that involve irregular hand movements, such as racket sports, make it harder to get an accurate heart rate reading from the wrist. When playing these sports, you can switch the handedness of the tracker and change it to the non-hitting hand. If you perform activities that cause extreme pressure on your wrists, such as weightlifting or pull-ups, your heart rate may be more difficult to detect from the wrist. However, regardless of the sport, you can always use the tracker to monitor your average heart rate and heart rate trends during the workouts, get accurate calorie burn readings, and use other Polar Smart Coaching features.

In cold conditions, blood circulation on the skin may become too weak for the sensor to get a proper reading. You can solve this by warming the skin on your wrist or by doing some exercise to increase skin temperature.

To maintain the best possible performance of the wrist-based heart rate measurement, keep your Polar device clean and prevent scratches. The measurement is based on tiny changes in light intensity, and even a small amount of dirt on the sensor at the back of the device can reduce its performance. Similarly, scratches on the sensor can scatter the light from the LEDs into unwanted directions and weaken the device’s performance.