pod said:
You seem to be confusing force and power. Any rider could produce 400 or 500 or perhaps even 600w for a short period of time just pushing down on the pedals but they are limited by their heart/lung capacity to a lesser sustainable output of say 300w for any greater length of time. The limiting factor is not the strength/force output of the muscles. Using a less efficient method such as pulling up on the pedals (or using your hands to drive a second crank for that matter) will not result in more power but less as more energy will be wasted by the less efficient method.
Why do rowers continue to use arm + leg muscles ?
Driving a second crank with the arm is not an efficient way to use the arms,
just as with pulling up with the legs reduces the concentration on the main
task of applying downward pedal pressure and results in less overall pedal
power, turning a second set of arm cranks will have the same effect. But
it is possible to put that arm crank power to better use and biomechanically
divert it back to the foot pedals. The use of this combined power is the
secret to more powerful, smoother and safer TT pedalling both from the
performance and medical aspects. This technique completely eliminates the
lower back from the pedalling equation and the smoother pedalling action plus
direction through which the power is applied to the pedal results in less stress
and strain on the knees when using the higher gears.