氣沉骨堅
Heavy vapours and strong bones
骨堅筋柔
Firm bones and supple fascias
As far as the body force is concerned, the external part, the most important was neither muscles nor even fascias for the internal arts, but it was the bones. Bones and force are the typical example of how internal arts work, body force was first about a stronger structure and, to achieve it, stronger organs.