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Re: Muscle work



At 05:00 PM 8/1/01 -0700, Tucker Hiatt wrote:

A key question is: How much? DOES A STUDENT DO AS MUCH WORK ON THE WAY
DOWN AS ON THE WAY UP?

In physics, the word "work" has a fairly well-defined meaning, or at least
a fairly tight cluster of meanings.

The use of the word WORK in the quoted question is very, very
unphysical. The fact that quoted hypothesis would even be considered for
more than a microsecond is symptomatic of either
-- highly nonstandard terminology, which will be a great obstacle to
communication with people on this list, or
-- some profound misconceptions about the physics involved.


1) The subjectively measured, constant-speed muscle force that I
apply is the same halfway up and halfway down.

That means that velocity-dependent "friction" or "viscosity" terms are
being neglected. That's probably OK in the low-velocity limit.

3) Long before exhaustion, power is probably the key
agony-determining variable; the faster work is done, the more it
"hurts". ("Agony" and "hurt" are not the right words, here; I'm
trying to be cute. But I don't quite know what words do describe the
subjective experience of doing a pull-up.)

Power is definitely NOT the right word.
Redefining fundamental physics terms is very unhelpful.

4) When the upstroke and downstroke are completed at the same
constant speed, it's remarkable how similar the agony levels are.

Which proves that work and power can't possibly be the relevant physical
quantities.

5) The turn-around motions at top and bottom are neither
energetically negligible nor equivalent. At the top of a pull-up,
the muscles involved have the least leverage, so the top turn-around
motion requires more muscle force and work than the turn-around at
the bottom.

Again this is a serious abuse of the word "work".

6) Psychologically, the top turn-around is something to be dreaded
much more than the bottom turn-around (for the physical reasons cited
in #5). So the upstroke is subjectively experienced as "bad but
getting worse," while the downstroke is "bad but getting better."

Strangely, I think assertion #6 may offer the best explanation for
why the upstroke is "harder" than the downstroke in constant-speed
cyclic exercises like pull-ups.

Really? I would think that plain old physics work -- you know, F dot dx --
would be a hypothesis worth considering as the "best explanation for why
the upstroke is harder".