In article
<
[email protected]>,
"Ken Roberts" <
[email protected]> wrote:
> Tim McNamara wrote
> > Measured pedal force data on standard crank (Okajima, 1983)
> > arrangements has found that 100% of the forces moving the pedals
> > push down- not necessarily straight down but within 20-30 degrees
> > of vertical.
>
> But "pedal force" is not what my mechanical efficiency claim was
> about. My claim was about force exerted by the hip flexion (and also
> some by knee flexion) muscles on the _leg_, so the muscular force
> lifted a portion ("lightening", "unweighting") of the weight of the
> leg, and some force from the pedal lifts the leg's remaining weight.
>
> So downward force on the pedal during the upstroke is just what I
> should expect to be measured, based on my explanation and numerical
> example.
Unfortunately your explanations have been sufficiently convoluted that
it's not easy to make out what your point is. It seems to change from
post to post. You initially tried to claim that pulling up is more
efficient than pushing down due to something about the force being
transmitted through the ankle and such. Now you're apparently saying
that lifting the ascending leg results in more net power to the
descending pedal. Well, yup, that'd be true but it's just not something
that happens much- only when you focus on it.
> The net force between pedal and foot in the upstroke is the vector
> sum of: (a) weight of the leg; (b) upward lifting of the weight of
> leg by its own muscles; (c) resistance or stiffness by the leg's
> down-push muscles not yet relaxed from their previous big push. So .
> upstroke pedal force F = - (a) + (b) - (c)
As the descending leg pushes down, the ascending leg is lifted by the
pedal. The upward lift is resisted by the weight of the leg and by the
viscous resistance of the muscles. It's unlikely that there's much by
way of "unrelaxed" muscles resisting the pedal stroke unless you are
having muscle spasms or some sort of neuromuscular malfunction. Muscles
relax pretty fast, especially in trained cyclists.
> Perhaps (a) the effective weight of the leg on the upstroke pedal can
> be reliably estimated in advance of the performance and will remain
> stable through the whole upstroke. But it's pretty hard to directly
> measure (c) the resistance of the down-push muscles, and it changes
> during the upstroke. So if you can measure only F and (a), but not
> (c), then you don't have a way to estimate (b).
Why? You use a strain gauge on the crank and measure the force of the
foot against the pedal. This has been done already, and I have already
cited where you can find the information.
> Therefore I'm surprised that some people are so sure they know that
> (b) is small. Still looking forward to the evidence that, "this ...
> has been tested scientically".
You've been told where you can find the evidence. (b) is vanishingly
small as in nonexistent according to the measurements. The exception
would be the Power Cranks which cannot provide lift to the ascending leg.
> P.S. Given the nature of the unmeasurable data component, it's much
> easier to use an inequality relationship to show that the Work of
> force (b) is _large_ in at least one important study, and that's what
> I did recently in the thread on "Coyle Kautz 1991" study.
What's unmeasureable about it? Strain gauges on the cranks will measure
the force magnitude and direction. Heck I think that you can measure
this at home with an SRM power meter and graph it out on your computer.