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Tenpat t1_ja5nfvv wrote

As a fellow with dry hands: they don't.

They use the bit of moisture most people have on their hands to measure resistance from one hand to the other. Along that path is your heart and its beating changes the resistance so by measuring it over time the device can tell your heart rate.

But if your hands are dry then they can't get a good electrical connection and don't read anything.

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Few_SIice3225 t1_ja6brdk wrote

Do you not sweat when you work out?

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Tenpat t1_ja6fkzp wrote

I sweat pretty much everywhere fairly profusely but my hands just don't get super sweaty.

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gmtime t1_ja4wm7h wrote

Blood conducts better than tissue due to the water in it. Those pads measure your skin resistance, which varies with your heartbeat

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Sea-Neighborhood729 OP t1_ja4xfqq wrote

What is skin resistance?

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manofredgables t1_ja52zg7 wrote

Electrical resistance. How much current you're conducting when exposed to the tiny voltage in the handles. It's a tiny current, but not too difficult to measure. Way below what you'd feel as an electrical shock.

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gmtime t1_ja52zjf wrote

A measure of electrical conductivity

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Sea-Neighborhood729 OP t1_ja5c5la wrote

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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snash222 t1_ja51l5v wrote

But it works while jogging? How does it manage to find the pulse amidst the constant changes of pressure?

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