Originally Posted by Brian Ratliff

The formula is correct, however, I am getting 60lbs. Remember that baked into the formula is "average power around full pedal revolution". One leg takes the cranks half way around, the other the other half, so each leg sees 60lbs. This is an average, the pedal force is likely starts at zero and ends at zero, smoothly rising to a peak and decaying back to zero. An estimate for the max power from this pulsation is double the average, or 120lbs peak force.

Also consider that this is also assuming the force is applied tangential to the pedal rotation. In actuality, the force is applied pretty much vertically. The 60lb average is referring only to the tangential component and not to the radial component meaning the average force the leg needs to put out to maintain 300W at 60rpm is probably quite a bit higher than 60lbs.

Given all this, the assumption that power is applied over only half a crank rotation in two quarter turn pulses is probably a good estimate. This would have each leg seeing about 120lbs of average force to turn the cranks at 60rpm. At 90rpm, the legs will see 67% of his, or 80lbs. For the average cyclist, this is like the difference between quarter squatting with just the bar (90rpm) and adding a couple 45lb plates (60rpm).