Abstract

Heart rate recording is a very useful parameter for the control and
planification of sport training. There exist various systems of cardio tachometers in miniature designed and specially made for their use in physical-sporting activities. All of them are placed on the chest by means of an elastic band, which provides an insufficient fastening for swimming, especially for the turns, so this forces us to use adhesive tape or other systems of “painful” fastenings.
The system developed in IBV (Biomechanical Institute of Valencia) allows us to record and send telemetrically the heart rate to a personal computer where we can show the actual time and/or be stored for its later analysis. In this way, the trainer can control the intensity of a training session and can send an almost immediate feedback to the swimmer.
The system consists of a peg placed on the ear lobe with a red light transmitter (LED) and a resistance depending on the light (LDR). The red light passes through the lobe and is received by the LDR. The grounds of the system consists in that the diminution of the red light in the ear lobe is associated with changes in the contents of oxygenated blood, a method known as “oxymetry”.
For the system of telemetry we used a sign modulator based on an oscillator controlled by tension (VCO) and a hybrid commercial circuit for the transmission. The calculation of heart rate in actual time is possible thanks to the use of a digital filter and the development of an algorhythm to reduce the noise.