If you overstretch in such a way that you increase your flexibility more than your muscular strength can resist to maintain a safe range of motion you are more likely to have joint dislocations. The way that I was able to build up to high side kicks and roundhouse kicks was actually by working a LOT out of a low horse stance--it's a combination stretch and strengthening exercise. That and you can also injure tendons and ligaments. He should just take it bit by bit, this is a marathon and not a sprint. He'll get there unless he has some physiological issue that he is unaware of. I would suggest that if he does experience anything unusual that he should go see a physiatrist. However, if his issue is just lack of flexibility, all he needs is to work on it and give it time. Thanks for the advice. I will try to come up with a comprehensive way to gradually increase my flexibility while building lower body strength. Have any of you guys used the elastic steel dvd and book? I have read some pretty good reviews about it on the internet.