What determines the amount of power of any given force is the proper mass coupled with velocity. Force equals mass times acceleration  f = m x a. Regardless of how much you weigh, an effective strike needs the right amount of body mass behind the strike to create the knockout power you're looking for. Think of like this; Try breakina window by throwing a plastic whiffleball ai it. No matter how much effort you out into the throw you will never break it. Why? The whiffleball has no weight to it. Even though you can get the ball to move relatively fast, the mass that makes up the ball is too light. Now try throwing a 16lbs shotput; now the opposite effect will occur. Being the shotput is so heavy, it definitely has the mass to break a window, but you may not have the strength to create the velocity to even hit the window. So you can start to undertand the force-velocity relationship don't match up with these two examples. Now, throw a baseball at the window and you'll break it ten out of ten times because the force-velocity curve match up