Taiji Power Secrets
It is not opening/closing but rather coiling/uncoiling and compressing/releasing.
It is not about using no force but using enormous amount of forces to maintain the rigidity of the structure, the integrity of the core and the efficiency of the move.
It is not about balance but balanced forces.
It is not about flexibility but the ability to stretch to produce a split or separation
Source: https://practicalmethod.com/?p=56204