According to my author friend Dr Bruce Clayton who wrote Shotokan's Secret, there are two major styles of karate - the hard style and the soft style. This has nothing to do with the intensity of training. His definition of the hard style is that system that uses linear acceleration as the predominant method to generate power. Hard stylists can be lithe, little, short, and yet can generate massive amounts of power from the acceleration of their bodies. Soft style karate practitioners on the other hand train their bodies up to withstand a lot of punishment. They strengthen muscular strength in order to apply loads of power from standing still. Their massive forearms attest to the power they can apply in their vice like grips.
Today while teaching our white (almost yellow) belt the soodo or shuto knife hand strike, I offered him my arm to strike while I took turns striking his forearm. Obviously as the beginner and someone who is taller than me by at least 5-6 inches there were many times when he tried to use muscular force and strike my hand with his knife hand technique. It resulted in a slow strike with my arm being pushed away. My strike however struck fast, extremely hard, and was a bone jarring technique that need only be felt once or twice before you're obligated to change sides.
The difference is that once the technique is learned, you need to give yourself the permission to relax more up front and accelerate much more throughout. The distance is not that great, so the differential in speed is key to making this a lethal technique. Obviously the kime or focus during the strike and the drop of centre of gravity is also required to add a lot of power to the strike. Once this was discussed, the power he created started to improve very very quickly to the point where I was unenthusiastic about using my arm as the target. :-)
Comparing the different hard styles is by no means offering disrespect - it is just that we need to recognise what each system is about and maximising our actions within those techniques. If we were working on a lot of Sanchin or building up our power and endurance ... then we'd be focusing on way different techniques and results.
Dan-gun: Knife Hand on Premium Unleaded even in Back Balance
Dan-gun Soodo: Don't get Slowed by the Fold
Traditional Taekwondo Technique Workshop