Unusual heart rate readings when using a Polar H9 or H10 heart rate sensor

Try removing any dirt or dried sweat by washing the strap in a washing machine in 40°C / 104 °F. Remember to detach the connector from both strap snaps and rinse the strap after every use. Wash the strap often and keep also the heart rate sensor clean. For detailed caring instructions, see Care instructions for a heart rate sensor with textile strap.

Proper care of the heart rate sensor and the strap after every use ensures good heart rate signal detection and longer lifespan.

Change the battery (CR2025) of the heart rate sensor. If the battery is running low, the transmission range decreases which may cause errors in heart rate readings. For instructions on changing the battery, see How do I change the battery to my H10/H9 heart rate sensor?.

To ensure a good contact between the skin and the chest strap:

1. Wash the strap in a washing machine in 40°C / 104 °F to remove any dirt or dried sweat. For detailed caring instructions, see Care instructions for a heart rate sensor with textile strap.
   
2. Moisten the electrode area of the strap thoroughly under tap water before training.
   • At the beginning of a training session your skin may be dry, and the moisture will help ensure better contact. When you start to sweat the contact will improve because the salt in the sweat conducts electrical signals very well.
3. Tighten the strap around your chest to fit snugly.
   • If the strap is loose, movement will disturb the electrically measured signal detection. If the standard-size strap does not fit satisfactorily, larger and smaller straps are available as accessories at polar.com. Note that the strap stretches over time and when it gets wet.
4. Move the sensor 4-6 cm to the left.
   • If the signal is weak when the sensor is placed right under pectorals (recommended position), move the sensor 4-6 cm to the left to find the best signal.
5. Try shaving a small area on your chest under the electrode area if you have a hairy chest.
   • If you cannot find your heart rate signal by positioning the sensor differently, shaving a small area for better conductivity may help.

Polar heart rate sensor measures the heart rate signal electrically from the chest, where the signal is the strongest. The signal strength cannot be influenced. The type of electrically measured heart rate signal slightly varies between individuals. The strength of the signal can depend on the shape of the chest, the anatomical location and position of the heart, the position of the electrodes, and the amount of body fat. If the electrically measured signal is weak, it can get disturbed more easily. To ensure accurate signal detection (needed before measuring is possible) the contact between skin and electrodes needs to be constant.

If you are using the heart rate sensor with a Polar watch and a certain sport profile constantly displays too low heart rate readings, check if you have set the sport profile to display heart rate in percentages of your maximum heart rate or in percentages of your heart rate reserve instead of beats per minute (bpm). For more information, see How can I edit sport profiles and training views in Polar Flow?.

Keep the receiving device in front of you to ensure sufficient transmission range. For example, a good place for a mobile phone is in a front pocket or handlebar. Bluetooth signal does not pass through human body, so do not keep the receiving device in your backpack, arm pocket or, for example, your hands behind your back while roller skating and using a watch as a receiving device.

If you are using the heart rate sensor with two compatible Bluetooth devices at the same time, turn 2 receiving BLE devices (Beat app)or 2 Bluetooth devices (Flow app) on. For instructions, please refer to Can I pair H10 with several devices?.

When you wish to use the heart rate sensor with an older Polar watch or gym equipment having GymLink (5 kHz) compatibility, check via Polar Flow or Beat app that GymLink setting is on. If you are using an ANT+ device, make sure that ANT+ setting is on. See How to optimize the settings of my H10/H9/OH1 heart rate sensor? for more information.

A fluttering shirt may rub the heart rate sensor and generate static electricity, if air humidity is low or you are cycling in windy conditions. This may cause additional signals, especially if the contact between skin and heart rate sensor is poor. To avoid this:

• Try placing the heart rate sensor 4-6 cm to the left.
• Moisten the electrode area of the chest strap thoroughly.
• Use a cotton shirt instead of a synthetic shirt.
• Use a tighter shirt to avoid fluttering of the material.
• Use the heart rate sensor on a wet shirt.

Polar devices are not designed to detect arrhythmia or irregular rhythms and will interpret them as noise or interference. In most cases the Polar training devices work fine for persons with cardiac arrhythmia, but in some cases (many abnormal heart beat intervals) arrhythmia may cause incorrect heart rate readings.

If you are using a pacemaker or other implanted electronic device, see more information in Pacemaker and Polar products.