This emphasis on speed and agility is a defining characteristic of taekwondo and has its origins in analyses undertaken by Choi Hong Hi. The results of that analysis are known by ITF practitioners as Chois Theory of Power. Chois Theory of Power is based on biomechanics and Newtonian physics. For example, Choi observed that the power of a strike increases quadratically with the speed of the strike, but increases only linearly with the mass of the striking object. In other words, speed is more important than size in terms of generating power. This principle was incorporated into the early design of taekwondo and is still used.