Destruction returns to my mind.
How about you start by considering the end goal of martial arts. You may pick among defense, destruction, body building, health, and showsmanship for starters. Then consider the structure of the human body, from bones to muscles and nerves. Then apply yourself to the question of how any transformation T on the set Body serves to achieve the chosen end goal. You will quickly learn about the reasons behind any set of Ts which may be referred to as a "martial art".