Well, yes, you do indeed strike with your muscle strength, guided by the structure of your technique. If you didn't use muscles, you wouldn't move at all Your core muscles and legs are providing the strength required to accelerate your fist, even though the upper body is relatively relaxed before impact. I am talking about functional strength, as opposed to raw muscle power. Yes, a video would be cool. The Hapkido punching I've seen just looks like Karate. However, don't concern yourself with the techniques the guy in the video is doing, only the principle of leading with the fist or leading with the hips and then allowing the fist to catch up. I very much like his analogy of a water-skier vs. a surfer. I'm not trying to "debunk" you. I'm just pointing out that your simple model is so simple as to be pretty much irrelevant in terms of how mass comes into play when striking. Plus, Ben gave the correct formula for kinetic energy: It's not a matter of blurring anything. The mass is not constant. If I hit you by only pivoting my arm at the shoulder, you are hit with less mass than if I keep my arm fixed but rotate my body around the axis of my spine.