The footage and graphics contained in the following (Chinese language) video are very interesting when it is understood that the bones are aligned, the bodyweight is dropping into the ground (rooting) and a rebounding force is rising. The mind is calm and expansive whilst the joints, limbs (and sections of the torso) are 'rounded' (concave and convex). When the joints are 'rounded' the ligaments and tendons are relaxed and extended (like a drawn bow-string). Although the muscle are relaxed and released from any unnecessary tension - there is a natural 'torque' (twisting tension) - again, similar to a bow-string that is drawn with just the right amount of tension - and no more.
This is important as most people are far too 'tense' and 'rigid' as a habit. Once the awareness penetrates the centre of the bones and all this is achieved - this advanced understanding spreads all over the body and is held in place by an expanded awareness. It can then be reproduced in any and all Form movements and in any self-defence situations. The bodyweight drops down through the centre of the bones (stimulating the bone marrow) and 'rebounds' up from the ground - also through the centre of the bones - and can be emitted through any part of the body. This power production can then be augmented by the localised speed of a limb or position (angle) of the attacking body-part. A perfectly timed blow can be massively magnified in power by catching an opponent 'running in' onto a punch or kick, etc. Here, in this beautiful Shaolin (Europe) video we can see how the bow is correctly 'drawn':
All this is achieved through holding the '站桩' (Zhan Zhuang) - or 'Standing like a Stake' - ('Holding the Ball') position. Although I focus upon the 'rounded' structure of this exercise - its name traditionally derives from a foundational 'stake' or 'pile' (shaped like a 'rounded' Western telegraph pole) that was driven deep into the ground (or sea-bed) which served as an anchoring (and firm) support for a building. There is 'rootedness' (dropped bodyweight) and there is expanding 'stabilisation' (rebounding and rising) power! This is an analogy worthy of further consideration - as it is this psychological and physical 'roundedness' that makes all this ability possible!
Shifu Adrian Chan-Wyles (b. 1967) - Lineage (Generational) Inheritor of the Ch'an Dao Hakka Gongfu System.