I don't want to derail your thread, but what you're starting to get at is "internal" movement and training, such as is developed in high level chinese arts like Taiji (and hopefully in Aikido, though its debatable how many Aikido teachers have this type of skill).
One of the goals of internal training is to develop and utilize the connective tissues of the body, especially the fascia. This is what gives high level martial artists (like O-Sensei) such "supernatural" strength.
Sanchin is certainly an important kata, but I think you may misunderstand its purpose. The goal of the Sanchin kata is specifically to develop this type of "internal" strength. By tensing the body so much, the kata stresses both the muscles AND the connective tissues. But the goal, overtime, should be to let go of this tension. Or more specifically, overtime the practitioner should learn how to relax the tension in the muscles but maintain the tension in the connective tissues. Look up Kenji Ushiro, as seen in [this video performing Sanchin]
. He's not all tensed up.
The methods in Systema, though less developed, I believe have the same effect. I believe the combination of awkward conditioning exercises (you should google some of their warm-up exercises) and emphasis on relaxation in movement, builds up the connective tissues while relaxing the muscles.
You can get more info over in the "Non-Aikido Martial Traditions" forum.