Physics of Striking in Combat Sports I was reading a blog post about the "physics of muay thai kickboxing" (https://heatrick.com/2013/10/13/the-science-of-muay-thai-lesson-1/) in which the author states that the main perspectives to consider here are Newton's second law of motion $F=ma$, and that the equation for kinetic energy $K = \frac{1}{2}mv^2$ tells us that speed of a strike is more important than mass since we square the velocity in the equation. Mathematically the reasoning made sense to me, but after reading a comment below the article I became concerned that maybe the model here is too simplistic:
"Your simplistic approach is only valid for rigid bodies (i.e. theoretical solid non compressible masses, which you are not).
This is highschool level physics, but it's far more complex than you are aware, and your approach is virtually useless, as the power of a punch is not from the speed or mass alone of the limb movement, entire structural moments and moments of inertia are important."
Since I am a mathematician with little knowledge of physics, I curious to know:
Are the other factors that the commenter mentions so significant in most cases that the aforementioned model would be rendered useless? Or if we assume perfect technique in the execution of strikes so as to maximize power, then is the author correct that speed should really be the contributing factor here?
Thank you for your time.
 A: Let me discuss a simpler case, as starting point for possibly extending the discussion.
The physics of hammering in a nail.
As we know from experience, if you have no room to swing the hammer you are in t rouble. You need a sufficient length of swing to get the hammerhead to a good speed. without enough room to swing the hammer even the strongest man in the world will not be able to do much.
The hammerblow:
You get the hammerhead up to speed, the hammerhead strikes the head of the nail, and the hammerhead is decelerated to zero velocity extremely fast. During that deceleration the force that the hammerhead exerts on the nail is many, many times the weight of that hammerhead. That huge force is extremely brief, but the nail does move.
When you are hammering and you get a rythm going, then by the time the hammer strikes the nail your arm is already relaxed, you're already done accelerating the hammerhead.
You can try to keep exerting muscle power as the hammerhead makes contact, but doing so is pointless. That bit of extra push is negligable compared to the force spike from the deceleration of the hammerhead.

So now:
Does any of this translate to some fist combat form?
Simplifying: fist combat, and winning is by knock-out, otherwise the fight is declared a draw.
(Just to be clear, I have no personal experience in any form of combat, I'm just generally assessing the physics.)
You get brain injury when the head suddenly rotates, in any direction. The worst punches to receive are ones that throw the head backward (rotation) and ones that turn the head violently (rotation).
It seems to me: only a fast moving arm has the speed to deliver a knock-out. Again, I have no personal experience, but from seeing footage of boxing matches: when two opponents are roughly equal then there just isn't time to get a big enough swing going. (No big swing; not enough speed for a knock-out blow.) It's only when one guy is outfighting the other that opportunities come to get to a big swing.
Of course, from seeing footage of boxing matches: many of the punches are in such a way that there is "weight behind it". But I'm guessing those punches aren't delivered with the goal of a possible knock-out, but for the purpose of wearing down the opponent in general.
So yeah, I guestimate that enough of hard body physics carries over to make comparison meaningful.

There is another aspect of physical combat that, I think, is worth thinking about from a physics point of view.
Is it an advantage to be tall? Only up to a point. For instance, among K1 champions Sem Schilt is unusually tall. If you have the upper hand, and your opponent is backing off, then you need to be able to close in quickly. But for a tall guy it's more difficult to lunge forward. In order to lunge forward your weight has to go first. You need to make yourself fall forward, and when you are tall that 'falling forward' takes more time. Remy Bonjasky was good at taking advantage of that. He could step in fast, deliver a kick, and step out of reach again. I remember watching an interview with Sem Schilt, and he mentioned that he had to figure out how to overcome his disadvantage; he could not move around in the ring as fast as his opponents could.
Note especially: the reason Sem Schilt was not as quick was not because he had more mass, but the fact that his center of mass is higher above the ground. The higher something is, the longer it takes to fall over. I just looked up videos of demolition of tall chimneys. The rate at which the stucture falls over is independent of the weight because inertial mass and gravitational mass are equivalent. It's the height that makes it slower to fall over.
