[From Bill Powers (2000.07.03.1021 MDT)]
i.kurtzer (00.07.01.1630)--
[Copy to Richard Kennaway, Wolfgang Zocher)]
I arrive in Boston (actually, at Kirk Sattley's house in Wakefield)
Saturday night before the meeting, and will have a car which I will turn in
on the Wednesday of the meeting. It's cheaper to return the car at the
airport and take a taxi back to BU than it would be to return car somewhere
in Cambridge. And I'll meet Wolfgang Zocher and Richard Kennaway at the
airport (around 1 to 1:30 PM) so we can share a ride back to Cambridge.
Richard and Wolfgang, this is mainly why you're cc'd in this post. Tell me
exctgly where and when your planes arrive. Wolfgang, I'm sending you a copy
of the paper mentioned below (Microsofr Word 97 with embedded figures --
hope you can read it).
So Monday and Tuesday (July 24-25) are at your disposal, Isaac; I can come
to Brandeis and meet with you and anyone else you can talk into a
miniconference.
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In the post I'm replying to, you say:
That may be the case but we can do our best to indicate what we mean by
words, using examples, counterexamples, and so on. So with effort people in
this setting mean, and the good ones convey this to the subejcts, that
effort is that feeling of trying such if I ask to to lift this object 200
times you would feel it was gettting harder and harder. That harder is not
a mass property of the weight or developed tension in your muscles. What it
corresponds to is debatable.
The nearest I can come to the situation you suggest is memories of doing
situps or pushups "to exhaustion," which was the fad when I was being
coached in high school. I never did it again, even when urged to. There
came a time when the pain level was higher than I wanted to experience, and
when the muscles simply failed to respond to an attempt to do one more
repetition. At that point I was "trying harder" in the sense of setting the
reference condition well beyond the state that would have been needed
without the exhaustion.
When I try to sort out what it means to say it got "harder and harder,"
these are the variables I think I can identify: the increasing level of
fatigue (mainly a burning sensation) to the point of pain, the decreasing
amount of perceived (and I would guess actual) muscle response, and an
exaggeration of the reference condition as I tried to make up for the lack
of effect. The sense of the exaggerated reference condition came, as per
PCT, from imagining the limb or body position in a state well past the
state I really wanted to achieve. This imagination thing, by the way, is a
lot like "reafference," isn't it?
The trouble with doing too much explanation with subjects is that you can
easily end up forcing your own metaphor or theory on them, or giving them a
plausible picture that they didn't have before. And when you're done, what
do you have? Some descriptions of subjective correlates of phenomena about
which you're none too sure. This may be interesting in its own right, but
I'm not convinced that it furthers our understanding of how the physical
system works.
The "most recent" paper of mine to which I referred is the one with the new
muscle diagram, and the comparisons of "experimental" model behavior with
results from McMahon and others. The last diagrams show a comparison of the
model's nonlinear force-velocity curve with McMahon's calculation of Hill's
curve using Hill's equation. The paper is now strictly meant to show that
the new muscle model produces all the observed properties of real muscle,
whereas the old series-parallel one doesn't. I'm going to present this
paper at the meeting.
I got a reference from Zev (William Z.) Rymer (to whom you referred me) to
_The Physiology of Excitable Cells_ by David J. Aidley (School of
Biological Sciences, Univ. of East Anglia, Norwicb, England -- where
Richard is!). The book (fourth edition, 1998, the latest) came in
relatively short order, and provides one or two added facts that will come
in handy for the model of the reflexes. It didn't help at all in answering
the question I asked Rymer. I don't think Rymer ever really understood what
I was asking, which is really pretty simple: are muscles in the totally
relaxed condition in the body subject to any tensile forces? And, of
course, if so, how much in comparison with the maximum contractile forces?
Rymer mentioned the soleus and sartorious muscles of the calf, and I can
see that when you lean forward there are forces developed, but would those
forces be the same if the muscle were curarized so no motor signals could
affect it? Also: Is it passive muscle stretch that limits joint angles, or
are there mechanical stops? I suppose the answer to that is "sometimes".
As I think we agreed the last time we talked, this isn't as important a
question as it seemed at first. The new muscle model can easily accomodate
any zero-point forces caused by a chronic passive stretch of a muscle a
little beyond its resting length -- a slight adjustment of the stretch
parameters will do it.
Let me know what arrangements suit you on the Monday and Tuesday before the
meeting.
Best,
Bill