Explanations:
You add the power of the arms, but that’s not all.
You can also add, at will, the power of your back and side muscles. These are much more powerful than your arms muscles. You can use these muscles separately or in coordination, at will. But that’s not all:
When the right pedal is in the best position to push on it, a little after the top, the right side of the bar is in its lowest position. It means that your right limbs are in the best position possible to push, for the pedal, and to pull, for the arm… Same for the left side, you guessed… But that’s not all:
The pedal is really efficient when near the horizontal position. The bar is always near the horizontal position. The pedal works through successive impulsions, the bar works more like a weight-lifting exercise. This means that when the pedal starts being pushed and is not yet at its maximum efficiency, the bar is already at its maximum efficiency. It does make a difference… (Notably when you get stuck in the mud with no more speed for the equilibrium…)