I'll expand on my point
"-despite claims of unusual strength, its promoters might just be waxing romantic about efficient use of normal strength, timing, balance, and relaxation"
a little bit.
In The Secrets of Judo
, a judo book from the 1950s (endorsed by the president of the Kodokan at the time, Jigoro Kano's son, Risei Kano), vectors are used as a teaching tool throughout the whole book. In fact, diagram 22 on p. 48 (and others elsewhere) looks like a lot of what we see in pictures from some internal strength people.
However, there do seem to be some important differences between approaches.
-The judo book uses physics as a teaching tool then moves on. That is, they aren't saying that if you don't agree or have a different opinion you or your teachers are unknowledgable, bordering on fraud, etc.
-The book emphasizes things besides ground force; gravity for example, as well as momentum, friction, impulsive force, and muscular force. That is, ground strength isn't their only focus or their main focus.
-They don't say the force is still unusual, which seems to be an appeal to the mysterious still even after talking about sciency stuff. They go out of their way to say that everything about it is quite ordinary.
-They present actual calculations that anyone can verify
-One can see examples of judo in action in free sparring sessions, demonstrating these principles. As a taijiquan practicioner, I admit that such things are rarely seen in taijiquan. We seem to do more fixed applications, or drills, things which may not translate 100% into real life.
-They show vectors on each throwing or grappling technique presented. In internal strength sources, they are mostly just shown with peng (ward off).
There are some other interesting discussions on physics in the book, for example
- interesting discussion about the nervous system and reaction time
- discusion on stablity of objects
- discussion on Newton's laws of motion
- calculations of force produced upon hitting the ground
- discussions on ukemi, how making the time t largest in Ft=mv to break the fall
- discussions on times where pushing off the ground with your feet might not be applicable
One thing that jumped out at me, is that if diagram 22 on p. 48 looks like a lot of what we see in pictures from some 'internal strength' people, it could be argued that it brings the whole internal vs. external thing into question, especially
when the judo book stresses relaxation a lot, and says things like ", he must learn to put into operation the principle of mind over matter", and "You will become one with him. You and your opponent will no longer be two bodies separated from each other but a single entity, physically, mentally, and spiritually inseparable"., things which could probably be taken right out of a taijiquan or aikido book.