The practice of relaxation bears two sides of effect: 1) the relaxation of muscles (discussed earlier); 2) the opening up of joints.
In movements mastered by muscular contraction, the joints in the skeletal system are, to different degrees, being bound and confined by their neighbouring contracting muscles (and probably those related tissues like tendons). The joints are not noticeably contributing power to those movements.
A joint, when allowed to move (expand and rotate), can give out unimaginable power of another kind that should not be simply ignored. It is believed that such power stems from the activity of ligaments (and the related tissues and parts) in a joint connecting two pieces of bones. Such “activity” refers to the deliberate movement of the ligaments on their own to cause the joint to move – not relying on neighbouring muscles to assist in, say, rotating. This means if the state of a piece of ligament remains relatively “stiff” (inactive), it will still restrict the freedom of the joint even though the neighbouring muscles have been satisfactorily relaxed.
When a joint is freed in this way, it is described as “expanding”. This “expansion” can be roughly viewed as two-stepped: 1) The joint is restored to its free state (it phenomenally expands) after the binding forces from the neighbouring muscles and tissues have been removed; 2) the joint proactively expands as the ligaments and the related tissues in it are becoming more active to cause the expansion. In general, the more a joint expands, the easier it is to rotate.
Proposition #2: Muscular relaxation, on one hand, brings about another kind of power of the muscles (i.e. Proposition #1; refer to the post dated 2013.10.10), and, on the other, frees the joints for deliberate movement on their own to start unleashing the power from the skeletal system. They are two sides of the same coin.