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).

1. 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:


1.1. Moisten the grooved electrode areas on the back 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 WearLink31 or WearLink W.I.N.D transmitter, it is essential that you moisten the electrodes well under the tap water before the exercise.

1.2. Tighten the elastic strap of the transmitter. 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.

1.3. 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 turning 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.

1.4. For active sports like aerobics or marathons, women can use the accessory Heart Bra which makes the transmitter stay in place better. Ask your local Polar dealer or distributor for the availability of this product.

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

1.6. In demanding cases, use conductive electrode lotion or gel to improve the contact. After using them, it is very important to wash the transmitter carefully. However, it is not recommended to use conductive electrode lotion or gel when using the WearLink31 or WearLink W.I.N.D transmitter since the lotion or gel can block the electrode area.

2. Wear and tear of the transmitter


WearLink31 and WearLink W.I.N.D transmitter connector and strap should be rinsed with water after every use. Dry the connector carefully with a soft towel. Store the WearLink or WearLink+ strap and connector separately.

Never store the transmitter when it is wet. Sweat and moisture can keep the electrodes wet and the transmitter activated, which shortens the battery life.


2.3. Do not bend or stretch the transmitter. This may damage the electrodes.

2.4. Only dry the transmitter with a towel. Hard-handed handling may damage the electrodes.

2.5. 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.


2.7. WearLink and WearLink+ straps should be washed regularly in a washing machine at 40ºC/104ºF or at lest after every fifth use. This ensures reliable measurement and maximizes the life span of the transmitter. Use a washing pouch. Do not soak, spin-dry, iron, dry clean or bleach the strap. Do not use detergent with bleach or fabric softener. Never put the transmitter connector in the washing machine or drier!

3. Electromagnetic disturbances

3.1 Transmitters using 5 kHz transmission frequency
- T31
- T31C
- T61
- WearLink31

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. Check your surroundings and move away from the source of interference, or remove the source of the disturbance.

3.2 Transmitters using 2.4 GHz transmission frequency
- WearLink W.I.N.D


3.3 Disturbance caused by electronical exercise equipments
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 monitor 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 running computer in this interference-free area as much as possible.
If the monitor still does not work with the exercise equipment, it may be electrically too noisy for wireless heart rate measurement.

4. The distance between the transmitter and the unit is too great

4.1 Transmitters using 5 kHz transmission frequency
- T31
- T31C
- T61
- WearLink31

The maximum transmission range between the transmitter and the unit is 1 meter (3 ft). If the distance is greater, the unit may not get all the 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 1 meter.

5. Signals from more than one Polar Transmitter within 1 meter transmission range
Note this is valid only with non-coded 5 kHz transmitter!

In cases where there are more than one transmitter nearer than 1 meter, and you are using the non-coded transmitter, your unit can pick up the signal from all transmitters within the range. This can result abnormal high readings. 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 a coded transmitter and unit, check if the code has been locked. After a successful code search, 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 the code search. 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 uncoded transmission is needed.
6. 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:

6.1. Moisten the electrodes before use, or use the conductive lotion or gel
6.2. Use a cotton shirt instead of a synthetic shirt
6.3. Use a tighter shirt to avoid fluttering of the material
6.4. Use the transmitter on a wet shirt
6.5. Wet the shirt

7. Arrhythmia
Polar products are not designed to detect arrhythmia or irregular rhythms and will interpret them as noise or interference. The computer in the wrist unit will make error corrections, so that arrhythmia beats are not included in the averaged beats per minute. The blinking heart symbol in the face of the unit, however, will continue to show all heart beats received. In most cases the Polar products will work fine for persons with arrhythmia.

8. Battery of the transmitter is getting empty
The estimated average battery life of the Polar WearLink31 and WearLink W.I.N.D Transmitters is 2 years and other transmitters 2500 hours of use. 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.