Internal skill is the ability to move within the space of the body itself as opposed to simply moving the body through space. This is a key distinction to make in order to cultivate certain types of development and the skills such development leads to, i.e. internal skill.
In the martial art tradition this process is often referred to as separating the bones and pulling the tendons. This is not a set of practices, but rather a depth of attainment through practice. It is present in all three of the Classical Nei JIa arts ( Tai Chi, Xin Yi & Ba Gua).
If we want to develop the tendons and bones of the body we must find a way to load them and create conscious pressure to transform them. This is achieved through precise intention and alignment, which emerges in time with the clarification and quieting of the neuro -muscular system or "habit body" .
When our practice moves us past this habit body we find neutrality and the freedom of choice that arises with it. It is in this new awareness and possibility that real learning and change begins as the arts reveal themselves more fully and we are more able to comprehend what lies within the depth of our practice. Tension is a function of habit and only by emptying out the residue of habit can we truly soften the body and move deeper into our capacity for governance.
Through practice and time our somatic intelligence clarifies and we become able to make such distinctions which guide our practice with intelligence toward their intended goal of self knowing.