The heart rate of a subject during strenuous physical exercise is monitored accurately by feeding the plurality of electric signals of diverse amplitudes generated by transducers engaging the skin of the subject, to a variably controlled gain amplifier to adjust the amplitudes to within a predetermined...http://www.google.de/patents/US5417221?utm_source=gb-gplus-sharePatent US5417221 - Method and apparatus for distinguishing electric signal waveforms
