Let me add a couple of things. I played for a Zwei Liga team when I was just 18-19 in Germany, and what that level of play helped me to develop was incredibly strong legs for my bodyweight. I could usually out squat guys twice my weight without much effort. Additionally, from growing up and NOT wearing shinguards except during matches, my shins were already well conditioned prior to starting muayThai training nearly a decade later. It is a great complement and what I see with many Americans who play predominantly "throwing" sports like baseball is under-developed or even nonexistent leg power. The footballers that have come in to train generally pick up the mechanics of kicking and can even hit the pads and heavybag without nearly as much pain as the rest of the students. One last point though - my legs went through a rather radical transformation physically - my quadriceps and hamstrings are significantly leaner than my football days and my calves much thicker.