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Old 06-21-2012, 11:09 PM   #9
JW's Avatar
Location: San Diego CA USA
Join Date: Aug 2000
Posts: 561
yaaaay neuroscience!

Hi Janet! Thanks, I love reading (and thinking about) stuff like this.
I like where the article ended up, and I think he is right on about modulating plasticity by consciously increasing attention, and through slow movement.
And especially, the part about habitual "dead spots" is right on, and I think is the strongest part of the article from the point of view of advocating slow, mindful movement. I've come head to head with this little demon (bad motor habits / dead spots) many a time.

Other bits in the article I take issue with though. I wouldn't expect everyone to read this, but I mention these points as food for further thought/discussion in case anyone is inclined:

-going "easy" (low force values) is not equivalent to going "slow" (low velocity values). Both are important but the article seems to conflate the two. We should probably think about both, but we should keep in mind that they are separate things and don't have to always go together.

-all the talk about Weber's/Fechner's law is a little misplaced. The point is that the Just Noticeable Difference scales WITH the stimulus intensity. In the author's hip extension example, if you are recruiting some flexors along with your extensors, then it doesn't matter if you go slow or fast, hard or easy-- you'll be at 80% efficiency when going hard and 80% efficiency when going easy (because the accidental/habitual flexor activation will scale with the intentional extensor activation). So if 20% antagonism is too little to perceive at high intensity, according to the something like Weber's law, it will also be too little to perceive at low intensity. Of course, I am totally wrong if anyone knows of evidence of these "bad habits" staying constant instead of scaling with level of effort. My feeling (from personal experience) is that such internal fights get rampant as effort increases, so it is actually the opposite of what is written in the article.

-Where Weber's law could actually be defended as being important to slow practice, the author didn't mention: lets say some external force (not your own accidental recruitment of flexors when you are trying to extend) is being applied to you while you try to do something. This force is not something that changes when you go hard or easy (as is true for most forces that impinge on you but don't come from within you-- they are independent of what you are doing). So if it is 2 newtons in the left direction, it will be 2 N if you go hard and 2 N if you go easy. When you go hard, your force production will "swamp" the magnitude of this external force. But if you go easy, then you will perceive (and thus learn to deal with) this force much more easily. Slow, mindful kihon anyone??

Anyway, thanks, great to read and think about!

ps. Other forces that don't change whether you go easy or hard include:
-your own weight
-the ground reaction force coming up on your feet
Thus going slow and easy even without a partner can help you feel how what you do is either fighting or aligning with what the ground and gravity are doing.
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