Richard Vizins wrote:
Göran: The power needed to overcome the dead spots at 12-6 is neglectable since the pedals are moving basically horisontally. Powercranks advantage (?) is in the phase (9-3) when you are (or should be) actually lifting one pedal. With or without Powercranks the 12-6 position is virtually powerless simply because of the fact that your body can't produce much forward/rearward force in those two leg positions. Producing enough power to overcome the dead spot without actually driving the bike is no great task ;). The same thing could, arguably, be said about the lift phase too. The fact that you lift the pedal doesn't neccessarily mean that you actually add any power to drive the bike. Consider pedalling without any load (e.g. drivewheel off the ground): the power you need to do this (not much, eh?) is the power you need to "lift" one leg with the other and to overcome the dead spots etc.. This is the power Powercranks are guaranteed to give you... You CAN of course gain more, but not automatically.
I agree in the above, but that is also a gain. It's better to have a small contribution from the not downpushing leg, than a negative contribution. The pulling up/back and pushing forward power is of course less but it is never the less significant. Don't you agree?
Concerning the cardiovascular capacity I think you are confusing aerobic and anaerobic power. My point is that you CAN increase short term power by using more muscles, as Frederik illustrates with the racing brothers, in this case we are talking about the anaerobic power (limited by lactate build-up). This is what you can use for up to a couple of minutes of sprinting. The aerobic power is when you are below your lactate threshold power and this is always limited by the cardiovascular capacity and economy (ability to use energy in an effective manner). This is the power you use for everything but the sprint efforts. Fit atheletes can stay close to their lactate threshold and produce high power for extended periods of time, but even they can't go above it for more than minutes.
Yes I'm very familiar with these concepts. But my point was that if I use more muscles to move the bike, I will go anaerobic at a higher power output. I can easily observe this every time I'm out on the road. If I engage the pulling up/back and pushing forward muscles, my HR goes up and the speed increases _without_ going anaerobic and _without_ reaching my limit for oxygen intake. The "new" muscles get tired after a while and the powercranks are supposed to help overcome that problem by forcing a training adaptation of those muscles. I haven't tried it (mostly due to the price of the cranks) but I think the idea is a sound one.
Mvh göran