Let's see, if we follow the energy path from hand to ground, we have hand, elbow, shoulder, center, kua, knee, foot, ground.
To me, elbow power is just a component of the whole structure where energy can be focused - actually, all the other points in between those above can also be a point where energy can be focused depending on what it is you want to accomplish and where the external energy is coming from and where you want to send it - of course, your opinion and mileage may vary
Greg