hamstrings

The hamstrings are a group of muscles located at the posterior thigh. The group conventionally includes the biceps femoris (with a long head and a short head), the semitendinosus, and the semimembranosus. All except the short head originate from the ischial tuberosity, and their tendons cross the hip and knee joints, giving them two joint actions. The short head of the biceps femoris originates from the femur and inserts with the other hamstrings to form the common tendon that attaches to the fibular head.

In terms of attachments, the semitendinosus inserts at the medial surface of the tibia as part of the pes anserinus, while the semimembranosus attaches to the posterior medial tibial condyle. The biceps femoris long head inserts on the fibular head, and the short head also attaches to the fibula. The hamstrings receive arterial blood from branches of the profunda femoris and the popliteal vessels. Innervation is via the tibial nerve for the long head of the biceps, semitendinosus, and semimembranosus, while the short head of the biceps femoris is innervated by the common fibular nerve.

Functionally, the hamstrings extend the hip and flex the knee, and they assist in external rotation of the leg when the knee is flexed. They play a key role in walking, running, and jumping, and they control knee extension during deceleration.

Clinical significance includes a high rate of strain injuries, particularly during high-speed running or sprinting. Injury mechanisms often involve rapid stretch or eccentric loading, sometimes at the musculotendinous junction or proximal origin. Treatment emphasizes gradual rehabilitation with eccentric strengthening, notably Nordic hamstring exercises, to reduce recurrence. Severe ruptures or avulsions, especially at the ischial tuberosity in youths, may require surgical repair.