Knee Support. Can be used for training or general support. Supporting knee by providing firm support to knee joint with gentle compression over the kneecap and shin. Please note this item is sold as a single support not a pair. Sizing: Measure the circumference of the knee at the patella when knee fully extended. Small = 11-13" Medium = 13 - 15.3/4" Large = 15.3/4 - 18.5" XL = 18.5 - 21.5"