Hamstring

The hamstrings are a group of muscles located at the back of the thigh that function primarily to extend the hip and flex the knee. The core components are the semitendinosus, semimembranosus, and the long head of the biceps femoris; the short head of the biceps femoris is often considered part of the hamstrings, though it does not cross the hip joint.

Origins and insertions: most hamstring muscles originate from the ischial tuberosity. The semitendinosus and semimembranosus insert on the medial tibia, with the semitendinosus attaching to the pes anserinus. The long head of the biceps femoris inserts on the fibular head, as does the short head, which originates from the femur rather than the ischial tuberosity.

Nerve and blood supply: the tibial division of the sciatic nerve supplies the semitendinosus, semimembranosus, and the long head of the biceps femoris; the short head of the biceps femoris is innervated by the common fibular division of the sciatic nerve. Blood supply comes from perforating branches of the profunda femoris and surrounding arteries in the thigh and popliteal region.

Actions: the primary actions are knee flexion and hip extension. They also contribute to rotation of the tibia when the knee is flexed, with different muscles producing slight medial or lateral rotation.

Clinical relevance: hamstring injuries are common in athletes, especially during sprinting or rapid deceleration, due to high eccentric loading during the late swing phase of running. Risk factors include prior hamstring injury, fatigue, and inadequate conditioning. Prevention programs emphasizing eccentric strengthening, such as Nordic hamstring exercises, have been shown to reduce injury risk. Treatment typically involves rest, ice, compression, and elevation for acute cases, followed by progressive rehabilitation. Severe tears may require medical or surgical intervention and structured return-to-play protocols.