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Sea-Neighborhood729 OP t1_ja5c5la wrote

Reply to comment by gmtime in ELi5: How do those metal bits on the handles of cardio equipment measure your heart rate through your hands? by Sea-Neighborhood729

Ah okay. Is sweat able to interfere with this then? From my understanding, the sodium in sweat helps conductivity, does this impact it at all?

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twelveparsnips t1_ja5idu4 wrote

your hands have to have a bit of sweat on them to work, otherwise your skin has too much resistance to overcome.

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Sea-Neighborhood729 OP t1_ja5jkmi wrote

Could too much lead to an inaccurate result do you think?

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danceparty3216 t1_ja5o2p2 wrote

The measurement isn’t looking at the absolute amount of resistance, its looking at the resistance as measured many times per second and watching for a pattern. The pattern is your pulse. It generally looks like a sine wave, and we filter out measurements that dont fit that type of pattern. Sweat happens, and the total measurement changes over time, the wave might move up or down like a tide on a graph, but its still a wave. Because your pulse exists pretty much within a known range of frequencies. Generally, 40-200 beats per minute. We’re ok to just toss out the measurements that don’t make sense. Its okay if we miss a few - its gym equipment and you won’t notice anyway, we just keep saying the same thing until we can get good data again. If its been too long since we got good data, we just stop trying to measure it. Then you usually re-adjust your hands until the measurement starts working again.

Long story short, its not a perfect way to make a measurement but it works well enough that people can use it. We kinda know what we’re looking for, we know how to measure it, and the user will figure out where to put their hands to get it to display the numbers.

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