Re: Powercranks
"Andrew Bradley" <andbrad2002@yahoo.co.uk> wrote in message news:<mpdUb.191$Y%6.29781@wards.force9.net>...
> Frank Day <fday@powercranks.com> wrote in message
>
news:69319bd2.0402041042.43c8b552@posting.google.com...
> ><snip> Simply not fighting onself by completely unweighting the recovery leg is enough to account
> >for this gain.
>
> Surely that just just means you pull up instead of pushing down harder, where's the gain? (that's
> why I said i wasn't convinced when they used this argument in the study)
No, because we are humans and not machines so we do not have an unlimited ability to just increase
force. Muscles loose efficiency if they are contracting "too hard" so allowing the muscle to
contract less hard, because it doesn't have to push up the recover foot improves contractile
efficiency so more "work" is done for less energy. Since the pulling up leg is also at a low force
contractile state it will also be more efficient than the one alone. By spreading out the effort
allows one to come up to the higher forces if one needs to which is what allows the power increases.
Something has to explain the HR drop from 155 to 141 at the same power in 6 weeks and it couldn't
possibly be training effect, at least not in my experience. Perhaps it is another mechanism but that
is how I explain it.
>
> >Another explanation is that coordination changes such that forces are better directed along the
> >tangential improving efficiency.
>
> I don't see an obvious link between pedal force angle and efficiency.
The driving force is actually the torque, not the pedal force. The highest torque occurs when the
pedal force is directed at 90 degrees to the crank arm. Anything other than 90 degrees means the
muscle is contracting just as hard but doing less work than possible. It is simple mechanics. If the
negative forces on the recovery portion of the stroke could be eliminated and the forces could all
be converted to become tangential to the circle cycling efficiency could probably be improved close
to 35 - 40%. That is almost a doubling of what most people are doing now.
>
> An outside possibility is that there is less negative muscle work on the upstroke than on the
> downstroke. (There will likely be a bit of negative muscle work on the downstroke via one or both
> calf muscles being forcibly lengthened, perhaps a bit of antagonistic hamstring work.)
With Powercranks, it is impossible to apply negative force on the upstroke but the tests were done
on regular cranks so it might have occurred, In fact, it probably did, just less intense.
>
> But even assuming a perfectly efficient upstroke, we can't tell whether this kind of effect could
> account for the results since we don't actually know how powerful the upstrokes were. (It would
> have been nice to see pedal forces measured).
You are right. Additional study is required to be able to determine exactly the mechanism of the
efficiency improvement. My mechanisms are conjecture I admit.
