If any part of the system is impaired, then motion also becomes very restricted. This is a 2 part control system, as we look at motion from the hips, and also at the shoulder area.
The systems of the body in a healthy person are in perfect balance. Power training in excess, and done without regard to this "balance" while providing an increase in mass and therefore an increase in static power will restrict torque. This makes the power increase very inefficient!
Is inefficiency important? Yes because of energy loss! The harder movement is the more power is wasted and not applied. This is often referred to as "muscle bound."
The goal of the martial artist must be efficiency of movement. This is the true formula to creating power.
Kyusho Jitsu Power Principle - Gravity
This is a rather simple part, however it has generated a lot of questions. First I do not like the word "gravity" as it is overused and has never been proven. it is a theory which is fine. We are accepting observation as law, which is not the correct method of doing things. And most physicists are happy to admit this.
What we observe in life with objects falling is actually the law of density and buoyancy. This is why object fall to the ground and at what speeds they fall. There are many factors at play here. [a balloon is lighter than air therefore more buoyant]
For the purpose of a martial artist creating power is based on the idea that since our mass is denser than the air we move in, we will create more power moving in a downward arch versus and upward arch.
Upward motion require we overcome the inertia of our mass, while downward motion we do not need to overcome our mass because we are denser than air.
Now really the terminology does not matter. You can certainly call it gravity if you wish. I just personally prefer using "laws" versus "theory" whenever possible.