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Abnormal Heart Rate Readings During Exercise

There can be several reasons for abnormal or irregular readings during exercise. Due to the same reasons, heart rate may stay at the same value for a long time or the heart rate stays at zero (0).

Heart rate view during exercise
If your training computer constantly displays too low heart rate readings, check if you have set the device to display heart rate in percentages of your maximum heart rate (HR%) instead of beats per minute (HR). Most Polar training computers include this option. Instructions can be found from the user manual.

Poor contact between the skin and the electrodes of the transmitter
For accurate heart rate measurement, the contact between skin and the electrodes should be as good as possible. Polar transmitters measure the ECG signal from the chest, where it is the strongest. The weak heart-generated signals need to be accurately measured before the calculation of the heart rate. It is therefore important to ensure that the contact between the skin and the electrodes is as good as possible. Here are some tips how to ensure good contact:

• Moisten the electrode areas of the transmitter. At the beginning of the exercise 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 the electrical signals very well. Saliva is a good conductor as well. However, if you have a WearLink strap, it is essential that you moisten the electrodes well under the tap water before the exercise.

• Tighten the elastic strap. If the transmitter is loose, the movement of the electrodes disturbs the detection of the ECG signal. If the standard strap does not fit satisfactorily, larger and smaller elastic straps are available as accessories.

• The type of the ECG signal slightly varies from person to person. The form of the ECG signal can depend on form of the chest, the anatomical location and position of the heart, position of the electrodes and the amount of body fat. If the ECG signal is weak, disturbances can more easily spoil the signal. Find the best contact by placing the transmitter left or right, or place it lower or higher. There have been cases where the transmitter detects the heart rate better when it is turned upside down so that the Polar logo is upside down and facing out, or even when attached on the persons back with the Polar logo upside down and facing out.

• Hairy chest may also weaken the contact. Try to find the best possible position for transmitter.

• In demanding cases, use conductive electrode lotion or gel to improve the contact of T31/T31C transmitter. After using lotion or gel, it is very important to wash the transmitter carefully. However, it is not recommended to use conductive electrode lotion or gel when using a WearLink transmitter since the lotion or gel can block the electrode area.

• Wash the transmitter after use and pay attention how you store it.

Store the WearLink strap and connector separately.

2. Wash the T31/T31C transmitter regularly after use. The transmitters should be washed with a mild soap and water solution. Dry it carefully with a soft towel after washing, and hang dry the elastic strap. For detailed washing instructions, see T31, T31C Transmitter Maintenance. Never store the transmitter when it is wet, especially not in any kind of non-breathing material, such as a plastic bag or a sports bag. Sweat and moisture can keep the electrodes wet and the transmitter activated, which shortens the battery life. Make sure that the electrodes of the transmitter do not contact anything damp, such as sport towel or wet elastic strap.

Store the T31/T31C transmitter dry in a cool and dry place.

• Do not bend or stretch the T31/31C transmitter as it may damage the electrodes.

• Keep your Polar product out of extreme cold and heat. The operating temperature is -10 ºC to 50 ºC/ 14 ºF to 122 ºF. Do not expose the Polar product to direct sunlight for extended periods, such as leaving it in a car.

To avoid erratic readings, move away from possible sources of disturbance.

• T31, T31C, WearLink, WearLink Hybrid and WearLink Nike+ transmitters are using 5 kHz transmission frequency. With these transmitters electromagnetic disturbances may occur near high-voltage power lines, traffic lights, mp3 player, the overhead lines of electric railways, electric bus lines or tram lines, televisions, car motors, bike computers, some motor driven exercise equipment, cellular phones or when you walk through electric security gates.

• WearLink Hybrid and WearLink W.I.N.D. Transmitters are using 2.4 GHz transmission frequency. With these transmitters disturbance way occur near microwave ovens and computers. Also WLAN base stations may cause interference when exercising with the product.

• Exercise equipment with electronic or electrical components such as LED displays, motors and electrical brakes may cause interfering stray signals. To solve these problems, try the following:

1. Remove the transmitter from your chest and use the exercise equipment as you would normally.
2. Move the training computer around until you find an area in which it displays no stray reading or does not flash the heart symbol. Interference is often worst directly in front of the display panel of the equipment, while the left or right side of the display is relatively free of disturbance.
3. Put the transmitter back on your chest and keep the training computer in this interference-free area as much as possible.

If the training computer still does not work with the exercise equipment, it may be electrically too noisy for wireless heart rate measurement.

The distance between the 5 kHz transmitter and the unit is too long
T31, T31C, WearLink, WearLink Hybrid and WearLink Nike+ transmitters are using 5 kHz transmission frequency.

The maximum transmission range between the transmitter and the unit is one meter/ 3 ft. If the distance is longer, the unit may not receive all the heart rate signals sent from the transmitter. In cases where the transmission range is at it is extremes, for example rowing or biking where the unit is not attached to the wrist, the unit may display the same heart rate for a long time. To avoid this, keep the distance within one meter/ 3 ft.

Signals from more than one 5 kHz Polar transmitter
T31 transmitter uses non-coded 5 kHz transmission frequency. T31C, WearLink, WearLink Hybrid and WearLink Nike+ transmitters are using coded 5 kHz transmission frequency. The transmission range of all 5 kHz Polar transmitters is one meter/ 3 feet.

When you are using a T31 non-coded transmitter and there are more than one 5kHz Polar transmitters nearer than 1 meter, your unit can pick up the heart rate signal from any of the transmitters within the one meter/ 3 feet range. Even if the other transmitter is coded, and yours is non-coded, your unit may still give an inaccurate reading. To avoid signal crosstalk, keep the distance to the other transmitters.

The coded transmitter and unit system does not pick up the signal from other heart rate monitors. In case of false readings with coded transmitter and unit, check if the code has been locked. After a successful code search in the beginning of the exercise, a frame will appear around the heart symbol on the display (apart from Polar FT40, FT60 and FT80 display). If the frames around the heart cannot be seen start the measurement again and check that you are not near other heart rate monitor users, because they may interfere code searching. Also, high voltage power lines, televisions, mobile phones and other sources of electromagnetic disturbance may interfere with the code search, as well as keeping the unit too close to the transmitter.
Polar FT40, FT60 and FT80 training computers do not show a frame around the heart symbol because, unlike other 5kHz-compatible training computers, they can only accept coded heart rate signals and therefore no distinction between coded or non-coded transmission is needed.
Static electricity, technical sportswear and special conditions
If the humidity of the air is low, or you are exercising in windy conditions (for example high-speed road racing), a fluttering shirt may rub the transmitter and generate static electricity. This causes additional signals, especially if the contact between skin and transmitter is poor. To avoid this:
1. Moisten the electrodes before use, or if you have T31/T31C transmitter you can use conductive lotion or gel
2. Use a cotton shirt instead of a synthetic shirt
3. Use a tighter shirt to avoid fluttering of the material
4. Use the transmitter on a wet shirt
5. Wet the shirt

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

Battery of the transmitter is getting empty
If the battery of the transmitter is running low, the transmission range decreases and may cause errors similar to the ones listed above in this document. The estimated average battery lifetime of WearLink transmitters can be found from the corresponding user manual. The average battery lifetime of T31/T31C transmitters is 2500 hours of use.