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Comment by ordu | Hacker News Reader

I wonder why an artificial stimulation leads to fatique?

Is it due to a lack of a feedback from a muscle? Biology devised quite an ingenious muscles consisting of several bundles of fibers, and nervous system distribute work between somehow. But to do something like that one needs a feedback including pain signalling when a concentration of lactic acid is too high, so nervous system could react by relaxing the muscle (or maybe an individual bundle? I'm not sure) to enable blood to flow and to bring concentrations to optimal levels.

Or there is another reason? Maybe muscles are not completely functional?

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I don’t know the source of fatigue reported in the article. But I worked in this area a long time ago and observed rapid degradation in rats. Perhaps it was from the techniques we used, but I speculated that the electrodes only excited a fraction of the muscle, while natural excitation is more widely distributed and perhaps more coordinated (e.g., uniform or optimally not uniform).

> Or there is another reason? Maybe muscles are not completely functional?

People using the device probably haven't been able to use the muscle in question for months or years.

If that's the reason, wouldn't that just be normal rehabilitation pain, and not something to blame on external muscle stimulation in particular?

It sounds like they're talking about some kind of inconvenience that is experienced even by non-disabled users, involving how the system does position-holding.

Yeah, my guess is that it's relying on major muscle groups in ways that aren't ideal, because the regular way the human body would hold/balance involves additional muscles that are too small/numerous to target or just plain hard to artificially orchestrate.

I mean, try "standing still" in front of a counter or raised desk for a few minutes and notice all the subtle load-shifting your body does, even if you steady your balance with your hands. If we can't replicate that, then we need something like this workaround of soft-clamping joints in place before relaxing the major muscles.

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