Mike Sigman wrote:
...Also, if this power is truly to be powerful, you need to strengthen the legs and hips (suwari-waza, anyone?) and you need to learn to let the power flow up not only from the legs but from the ground on which the legs rest. You don't lift anything when you use this kind of power, you push things upward with the ground.
Shioda Sensei is said to have taught that kokyu power comes from the toes.
I've found that when practising suwariwaza kokyu-ho, if I manage to tune everything out except the sensation of the contact of my toes with the tatami, the technique becomes almost effortless. I'm still working on extending this to standing practice.