The semitendinosus muscle is one of three hamstring muscles located at the back of the thigh. The other two are the semimembranosus muscle and the biceps femoris. The semitendinosus muscle lies between the other two. These three muscles work together to bend the knee and extend the hip. The semitendinosus muscle begins at the inner surface of the tuberosity of the ischium and the sacrotuberous ligament. It inserts at the medial tibial condyle. The structure of the semitendinosus muscle is primarily fast twitch muscle fibers. Fast twitch muscle fibers undergo rapid contractions for a short time period and easily wear themselves out. The inferior gluteal artery and the perforating arteries bring blood to the semitendinosus muscle. A segment of the sciatic nerve serves as the sensory and motor nerve for the semitendinosus muscle. When the semitendinosus muscle becomes strained, a pulled hamstring is the result. There are three grades of pulled hamstring that are defined by how bad the muscle tear is and the degree of pain and disability.
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In Depth: Semitendinosus