Kiyoshi Arakaki has a book called "Secrets of Okinawan Karate" that explains (the best explanation I have seen yet) of the "gamaku" concept and how to use it for striking. Many chinese martial arts stylists use a whipping motion generated from the legs and spine...I believe this is part of the secret of karate's power as well. Don't take my word for it, check out Kiyoshi Arakaki's book. It is well worth the price, in my humble opinion.