I live in Boulder, Colorado. If you get into trouble socially in Boulder, all you have to say is the magic word, "sustainability." This works for all situations. If the police are trying to arrest you, just say, "sustainability," and they will let you go. If you step on someone's foot at the cafe, say "sustainability," and everyone smiles. If your dog barks at someone, if your goats get out of the yard and chew up the seats of your neighbor's convertible, if you forget a friend's birthday, just say "sustainability;" it is the universal safe word for Boulder. All advertising, marketing, education and politics uses the word "sustainability," in all situations.
In martial arts circles, where English is spoken, I often hear the term "bio-mechanics" used in a similar way. While the term "sustainability" never actually referred to anything real, bio-mechanics is a defunct field of kinesiology.
Bio-mechanics is the application of principles of engineering to human movement. In martial arts there are a handful of these principles which everyone should know because they are intuitive. Long levers are more powerful than short levers. Move the center of mass off of the base and the person will fall. To lift someone, get under their center of mass. Mass times velocity squared equals momentum.
On the other hand, the expression "bio-mechanics" is invoked by marital artists frequently to justify the use of "structure." To see if structure is actually involved simply do the technique while someone slowly and gently pokes you with a red-hot branding iron. If you move suddenly six or eight feet in the opposite direction, structure was not the original mechanism, because structure does not jump into the air and scream when it experiences pain.
Bio-mechanics has some utility. It can be used to analyse a javelin throw in two dimensions. But in three dimensions it is too complex to be practical. Yes, Usain Bolt, the fastest runner ever, has very short springy achilles tendons. And bio-mechanics would predict that. But there are plenty of people with short achilles tendons who are slow runners. The oddities of statistics and social biases being what they are, having the name "Bolt" is at least partially responsible for his great speed. He likely got extra positive feed-back and assistance from coaches, friends, and fans, because of his cool name.
The field of bio-mechanics came crashing down when someone wrote an academic paper attempting to analyse the movement of two basketball players dribbling down the court and passing the ball back and forth. Bio-mechanics could not explain it. It was too complex. It required a new theory, the theory of continuous, perception, action loops. Movement is not mechanical, it syncs with visual flow, predicts patterns and produces dynamic spatial maps.
However, academic fields do not die, people do. And once people have tenure at a university--they do not die, they become zombies. So bio-mechanics is still taught at universities.
Bio-mechanics is also used extensively in elite sports coaching. Obviously this is not science because it suffers from an extreme case of selection bias. Put all the best runners in a group and pick their coach competitively and whatever mojo-magic training routines they come up with will be "proven" superior. Bio-mechanical analysis is just light-weight baggage, verbiage for the experts to toss around. Meanwhile, already very fast runners practice running even faster. They use keen observation of the competition, and trial and error.
Why is this important?
Because martial arts are not bio-mechanical, they are interpersonal. The mistakes people make, and then justify by saying the magic word, "bio-mechanics," are errors of perception. A simple example is the idea of alignment.
The conventional error of perception is that "good" alignment improves structural power. This creates an astronomic number of problematic training artifacts. When people say, "alignment" they imagine they are referring to something purely physical. But humans communicate our social status through the way we stand. We stand differently in a crowd of athletes than we do in a circle of nerds. We stand differently on top of a mountain than we do in a shower stall covered with thick fuzzy mold. It gets weird. We unconsciously treat inanimate objects and spaces as if they were animate. That's why trophies are tall and shiny. We tend to stand up taller next to a trophy, unless we feel we do not deserve it.
People have tried to argue with me. Saying, for example, that they do not have social interactions with a tree. This has actually been tested by kinesiologists in Japan. People breath differently next to trees than they do next to freeways or buildings. Trees probably make our monkey brains feel safe. If we need to escape from a predator, we can climb up into the branches in an instant.
People do become habituated to certain postures, because tension held in the body communicates "character." This social-origin tension is inefficient for power generation.
I'm trying to point to something here which is hard to put into words. I can make fun of people in Boulder and their magic words, or academic fields that won't die, or coaching science, but these people all believe in what they are doing. My comic critique is not likely to change their minds.
The same is true for martial artists and "bio-mechanics." This magic word is used as a psychic defense mechanism to deflect people away from noticing the way social tension and competitive monkey dancing influences their movement. When predators are hunting, they do not fight; fighting is a social dominance activity. How can I break through this deflection?
A human is a bunch of bones and water in a chewy membrane called skin. Inside this membrane are other membranes stringing it all together. This water is mixed with various chemicals and compounds. All of this amounts to nothing but a chunky blob of mush. When this body is at 98 degrees and has an electrical charge running through it, it suddenly organizes into a cool shape! But without awareness of space and a dynamic imagination, this body will just lay on the ground shaking.
The bio-mechanics of alignment is an electrical feed-back loop triggered by the perception of space which organizes our mass so that it balances over our base. Every part of the body has to be balanced on whatever is beneath it in a continuous fluid electrical flow. Structure is simply an illusion of frozen time.
However, this "structural" illusion in an attacker is what allows the internal martial arts principle of counterbalancing to work. All incoming forces and physical resistance can be counterbalanced if the attacker tries to use their body in a structural way to generate power from the ground through their body.
Discarding the structural illusion also has healing power because without it, body parts tend to move toward the most efficient use of vertical space.
Physical movement principles are straight forward in the abstract. In practice they have to overcome all the ways we are socially resistant to freeing our inner predator.