See the preview here. I really like the explanation from 3:15 to 4:15 on why you should strictly keep your knee behind your toe. Am trying to use these rebound mechanics as yet one more factor in learning a hard soccer kick, and it seems to be working. I’m using the bagua toe out and toe in drill and some simple stretch reflex as well. Not getting it all just right yet but definite improvements in power are coming along.