The error of bending and stretching is a human epidemic.Â Not that it is a crisis or a struggle or a life and death situation, humans can freely carry on merrily bending and stretching from now until internal arts are in the Olympics (or eternity, which ever comes first).
Without shrinking and expanding it is impossible to get effortless three dimensional power; up/down, left/right, front/back, and spiral/turn.
When predators fight they always attack using whole-body shrinking and expanding.Â This allows them to simultaneously strike, uproot, and rotate their prey.
Predators are also very cautious about receiving injuries.Â Shrinking and expanding allows a predator to diminish the force of their prey's counter attack without reducing the force of their own attack.
Shrinking and expanding does not require strength, in fact, for the most part, strength will inhibit it.