Born in ancient Thailand, this deadly martial art was very brutal in it's old days. The fighters would have their fists wrapped and then shards of glass were glued to the wrapping. Training was like punishment; mainly focusing on strengthening the shins and knees. Pounding your shins against as hard a surface as you could find was a good way of conditioning. Speed and durability are the two main factors in muay thai. A well-experienced muay thai fighter can break a parking block with a few kicks.
Certain rules were later applied to form American kickboxing. Such rules as: No use of the knees and no elbows. Then, it degenerated into American boxing where only the fighters' fists can be used. Just like any other fighting style, there is a certain sense of grace and balance involved. But, you can't expect to be a feather-weight and excel in this style; a lot of strength is needed; both outter and inner.