Re: hiriki no yosei/elbow power #1
I'm going to slightly disagree with Boon on this...but I suspect it might just be semantics.
I think most of the weight should be focused on the balls of the feet. This is because if more weight goes into the heels then I believe you will start leaning backwards and since one of the many premises is that you should always have your weight forward then allowing too much weight on your heels would be a bad thing. Of course I've seen (and done) weight on the heels many a time <sigh>
However, I think Boon is right in that it is all about gripping the mat with your foot and having a good solid contact. To do this the whole foot needs to be touching the floor. And to be really solid I think you need to sink your hips down and tilted and push into the back leg as strong as into the first.
Fun with pivots. Try doing 365 degree and more pivots without losing your balance. When you get get it right so that you don't almost fall over it feels really good. Or 180 degree pivot crosstep back with partner...going as fast as possible, but without losing balance or bending over.
Other things we play with are to do all of the kihon dosa on our tiptoes. It really helps find out where your center is when the contact with the floor is minimized.
A few more yen into the pot...