Why is this the exclusive domain of "IP/IT/IS"?
In old school western physical culture, tendon strength or sinewy strength were commonly referred to. These elements have not been lost in arts such as wrestling, weight lifting, and gymnastics.
It's how they use that tendon strength.
There may be some traces of IS in ancient wrestling when Hercules lifts his opponent off the ground, breaking his ground connection, at which time the opponent lost all his strength.
However, in IS, the tendon and sinew are seen as part of a whole complex web unlike I've ever heard it described in athletics.
Further, in IS, this entire "connective tissue" system is the medium of "ki" in the body. Ki flows through the fascia/connective tissue. This also explains why some acupuncture points are on nerve points but others are not. The western approach is that these must be imaginary points and that only the nerves have any capacity to conduct energy, and that can only be electrical energy. But ki is in the whole connective tissue complex all the time. Traditional approaches moved and balanced the body in specific ways to shift the efforts from muscle to the connective tissue via ki movement.
That's a big difference in usage and the quality of the results can't be attained by Western sports and athletic methods. Otherwise, judo would have improved remarkably after its inclusion in the Olympics. Instead it became more like wrestling and less like an Asian fighting art, this according to Minoru Mochizuki.
So the use of the connective tissue in IS is completely different from Western sport and athletics.