Muscle · Hips

Semitendinosus

Musculus semitendinosus

Semitendinosus is the inner hamstring you can actually feel — the round, cord-like tendon standing out behind the inside of the knee. Its name says what is unusual about it: half of it is tendon. The belly is short and finishes around mid-thigh, and from there a long rope carries the pull down and forwards to the inside of the shin bone, where it joins sartorius and gracilis in a webbed attachment called the pes anserinus ("goose's foot"). It extends the hip and bends the knee alongside the other hamstrings, and once the knee is bent it turns the leg inwards — the opposite of what biceps femoris does. That long tendon is also the one surgeons most often borrow to rebuild a torn ACL.