Summary Semitendinosus Origin Posterior portion of the ischial tuberosity Insertion Superior aspect of medial portion of tibial shaft (pes anserine) Action Extends the thigh and flexes the knee, and also rotates the tibia medially, especially when the knee is flexed Innervation Tibial nerve (L5, S1, S2) Arterial Supply Perforating branches of profunda femoris artery, inferior gluteal artery, and the superior muscular branches of popliteal artery