I don't know. I haven't had this particular problem for a few years now. That was also the time I was really building my skills/strength as a cyclist, so it could very well have been just from overexertion and new muscle development. It was sort of like growing pains in a way. The stretching and vitamins seemed to help the most though. It doesn't help so much for stopping cramps that have already occurred, but for preventing them in the first place.