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# How does the trademill in the Gym calculate my heart rate ?

Hello Guys,

Just a quick question but I need a technical answer, you know those trademills in the Gym which you run on, you know when you put just both of your hands on those handle right infront of you, it displays your heart rate. How does it do so ? Please explain in as much detail as you can ? Does it capture the heart signal ? Does it just count ? How does it capture the signal ? Is it some electrical impulse in the hand ? Many ECG systems feed some small current back to the body (right leg drive) to decrease noise, how come this trademill calculates heart rate without any connection to the body other than the 2 hands?  Please explain

Kind Regards

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3 Solutions

Commented:
"how come this trademill calculates heart rate without any connection to the body other than the 2 hands?"
It doesn't,
It uses the electrical signal generated by the heart beat. Next time you are at the gym watch the heart rate when you let go of the handles.

(Just not let the gym supervisor see you do it or his heart rate will go up)
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Commented:
The principle is identical to the way hospitals monitor heart rate but you just have two connections.  When your heart beats an electrical impulse moves across it and as it is basically a huge muscle the heart contacts in response.  What the electrodes on the treadmill measure is this electrical activity.  Because there's no third lead there's a fair amount of interference from other electrical signals from muscles but the electronics in the treadmill are smart enough to know they are looking for a regular rhythm of between around 50 and 180 beats per minute so can filter out a lot of the background.  Not sophisticated enough to make a nice ECG/EKG signal but enough to count heart rate.

Some of the science here

ECG systems don't feed current back along a third wire, they use the third wire to look for artifacts to clean up the outgoing signal.
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Commented:
Medical ECG systems use up to 10 electrodes, placed at strategic points around the body, for diagnostic ECGs. The signals measured differentially between various combinations of these electrodes then allow the physician to interpret the behaviour of the various components of the heart's conductive system.

See e.g. http://en.wikipedia.org/wiki/Electrocardiography

Essentially the two conductive handles on the treadmill are the equivalents of the wrist electrodes on a medical ECG measurement setup, and the electrical signal amplitude at the handles (in the microvolts region) is sufficient for the electronics in the treadmill to be able to amplify and extract the pulses needed to calculate heart rate. Filtration of the extraneous noise is key, in particular a notch filter centred on the mains power frequency and high and low pass filtering, suitably tailored to maximise the cardiogenic potentials, together with gating designed to ignore "out of sync" pulses.

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