My knee is exactly 40cm in diameter and as I am a stocky guy I decided for safety for large, a good decision! To (triceps surae'm sorry, no German) the calve muscles-is the bandage being too tight, it is probably because I have huge calves as I often this train, so prefer to buy slightly larger than small. Once the rail is seated properly, but she sits well! My left knee makes you one month while running increasingly stress, last week went off 4km nothing more, but now with rail after 7,5km at a faster rate, I have the entire run course NOTHING felt in the knee. Even some hours later not, my knee and I are therefore highly satisfactory. The entire support has not very high, only the locks. For me, this is not a problem but as the bandage fits like a glove with or without closure. Running She has not bothered / hurt / irritated / slipped or what one can else imagine. The part sat bombproof and has my foot even in the correct running position forced. My conclusion: For stronger legs rather buy one size bigger, but it is now definitely a great product! I apologize for my bad German and unprofessional writing, but up here, no one has determined eh read.