The causes of posterior hamstring pain are as follows: 1, strain on the popliteal nerve: for example, often in doing leg presses, if the knee press is too strong, it can cause hyperextension of the knee joint, which can result in strain on the joint capsule or popliteal nerve at the back of the knee joint, and therefore manifest as pain behind the knee. 2, popliteal cyst: often due to the joint fluid in the knee joint flowing out from the weak point at the back of the joint capsule and accumulating in the localized masses form at the popliteal fossa. When walking too much, the lump in the back of the leg often increases in size and is accompanied by a significant feeling of swelling and distension. The presence of popliteal cysts generally requires arthroscopic surgery to remove the cysts so that they can be completely prevented from recurring.