Re: Fast pedalling, why? Re: How many gears are enough?

On 2009-07-09, jobst.brandt@xxxxxxxxxxxxxxxxxx <jobst.brandt@xxxxxxxxxxxxxxxxxx> wrote:
Ben C? sniped:

[...]

This is not true. Measurements have been taken on force applied
to pedals, and at anything above very low cadences, there is
significant force applied to the pedals at the bottom of the
pedal stroke and significant energy used in changing the
direction of the mass of the legs at the bottom of the pedal
stroke.

Force application studies have shown that useful force is applied
only through a short section of the pedal stroke.

Did they also show that useless or counter-useful force is applied
during other sections of the stroke?

By useless force, I mean force applied without doing any work-- such
as pushing straight down at the very bottom of the stroke.

By counter-useful force, I'm thinking of pushing down on the
up-pedal, which some inexperienced riders may do just to keep their
feet securely on the pedals.

But any energy you put in, at any point on the pedal stroke, goes
into turning the crank and pushing the bike through the air (minus
losses in the usual places-- friction, damping, etc).

It's all good, it doesn't matter whether you're putting energy in
around the bottom of the stroke, on the downstroke or even on the
upstroke (apart from more subtle physiological considerations).

Fortunately this claim is readily testable. Position a pedal at
the bottom of the stroke and then put your full weight on it- how
much of that force is translated into forward motion?

None, but you haven't done any work either, so the efficiency is
100%.

In order to put energy in right at the bottom of the stroke, you
have to push the pedal horizontally backwards.

Ooh! We are being reintroduced to "round pedaling" subject which
suggests that power can be generated out of nothing by additional
muscular effort.

Well, force x distance is work, and you can "round pedal" if you like--
so long as you force the crank round in the right direction, you're
adding energy to the bicycle's motion.

It might not be a particularly helpful pedalling style though.

As mentioned in the past, this hypothesis can be tested by
intermittent pedaling while at maximum speed on a level road.
Counting 1-2-3-1-2-3-1... synchronous with the downstroke of each
foot, and then pushing down only on the count of "1" the same speed
can be maintained with the same effort. Although this is tedious and
brings no benefit it works.

Yes, I would expect that to work too.

The point is the muscular effort goes into the cranks while adding
gratuitous muscular force (round pedaling) does not enable a rider to
go faster other than in a burst (sprint). Continuous bicycling is
power rather than force limited.

Yes, I think so most of the time-- that's why we have gears anyway, so
you can keep it power-limited.

But there may be some benefit to lifting between 0.5 and 1.0 times the
weight of the leg on the upstroke. You're using some different muscles
to add a little bit of work, or maybe it improves circulation or
something. I don't know, but it feels comfortable on the bike. YMMV.
.

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