kmurdick wrote: ↑
Sun Oct 28, 2018 6:07 pm
But there are two kinds of flexion and extension: voluntary and involuntary. If you start with your fingers in mid range and rapidly close the fingers into a fist, this is voluntary flexion. It after closing the fingers into a fist, you relax the fingers, they will return to to mid range - this is involuntary extension. Voluntary extension/flexion will cause fatigue if there is no relief. Involuntary flexion/extension will not cause fatigue and can offer relief.
I don't know that all this is as established as you seem to present it. Some thoughts:
1. If you relax the fist it goes back to a less flexed state not because of "involuntary extension", but because it took a force to keep it in 'fist state' and as soon as you stop applying it (without applying any other muscle force - involuntary or not - it goes back to a stable state where various internal forces from tendon friction and elasticity are balanced. Therefore I don't think this example illustrates your concept.
2. I think by voluntary and involuntary maybe you mean conscious and subconscious (there is a difference). Insofar as subconscious relates to mental 'chunking', I agree that progress seems to require it in order to avoid one part of what we feel as fatigue.
3. As to the feeling of fatigue, it seems to have 3 components: a) conscious micromanaging of a complex motion (vs. chunking); b) not letting muscles have a break (vs. applying a very brief impulse-like force exactly when needed); and c) erroneously engaging muscles which are not involved in the motion (vs. only using the muscles needed). c) and b) can be compounded in using the wrong muscles and
forcing them to fire without a break. All three aspects have to be worked on, not just a).
Somewhat related, I don't get the "ballistic motion" argument - which implies through its name that one's finger resets due to gravity. The fingertips are not akin to free-falling objects - there is resistance from tendons and muscles restricting a freely-unfolding finger; also a finger/tip unfolding has to pull on the flexor tendon and push the extensor tendon out of the way. This makes gravity a minor force in the mechanics of returning a fingertip to its pre-stroke position.
I think extensors are always employed to varying levels, regardless of whether the person feels that or not. More so when speed is important - there is just no time to wait for some sort of slow friction-mediated gravity "fall" to reposition the fingertip to its pre-stroke place. We also now have published studies involving actual measurements, and they show the extensor firing to return the finger. It is another matter whether we feel that.
What do people think about this?