i know that since I started tae kwon do and cardio kickboxing mine have gone WAY down...all that kicking. What is really good are these kicking drills we do where you put one hand on the wall for balance and pickup the opposite leg and do lots and lots of kicks without putting your leg down - side and roundhouse kicks. That area of your leg just burns when you do it so you know it is working... you can also do the drills on the ground, lie on your side and kick with the topside leg. Maybe this will help?