During workouts, an endurance athlete used to check the heart rate on his wrist or neck but to do it he had to slow down or stop. As the workout intensity decreased, the heart worked slower and the heart rate dropped. The longer he was standing while holding his fingers on the neck, the lower his heart rate was. A one minute long examination was senseless. To get the right measurements, an athlete had to check his pulse only for 10 seconds not to lower his heart rate too much. The result was multiplied by 6 which gave rough and imprecise data. Unfortunately research showed that this method of calculating heart rate led to errors as high as 9 beats per minute. Next research established an error at the level of 17 beats per minute. But what athletes could do?
It became clear to coaches and athletes that this method of calculating the heart rate was too inaccurate, and medical devices designed to measure the heart rate were too expensive and too big to carry them around. Small, inexpensive devices were needed to check the heart rate during workout not while resting.

In the 1970s, two turning points occurred. At the beginning of the decade the Australian sport psychologist, and later world-famous swimming couch Dr Robert Treffene began to work on heart rate measurements. Soon after, he created a pocket monitor with electrodes and cables that enabled him to check heart rates of swimmers right after they had finished swimming and stopped at a swimming pool wall.

The second breakthrough came in 1977. There was Seppo Säynäjäkangas 33-years-old professor of engineering in the Oulu University at the west coast of Finland, a keen skier as many Finns. In 1976, he wanted to help a local skiing coach frustrated by the lack of possibility to monitor heart rates of his beginner athletes. The professor invented the battery-operated heart rate monitor placed on the fingers tips. He knew he was ahead of something big, as the Finnish national team of ski race wanted to use the device, so he founded the Polar Electro Oy company in 1977.

A year later, Polar launched the first heart rate monitor Tunturi Pulser. The heart rate monitor was connected with the chest strip using cables. 5 years later, in 1983, Polar showed his first heart rate monitor that was using an electric field to transfer data – Sport Tester PE 2000. In the following year, the company launched the device with a computer interface – Sport Tester PE 3000. The era of modern training has begun...

The strap transmitter consists of two electrodes measuring the heart activity through skin. Collected in this way data are sent to the receiver i.e. the watch that not only displays the data but also stores them. Nowadays, watches are small, equipped with many functionalities, and also become a fancy jewellery for athletes worn not only during trainings.