The hamstring comprises most of the muscle bulk in the back of the thigh. It is important for pushing off, jumping and landing and especially when riding for ensuring good contact to the saddle. The hamstring is made up of three muscles - the biceps femoris, the semitendinosus and the semimembranosus, each with a common proximal attachment via a large tendon to the ischial tuberosity of the pelvis (the large bone you sits on in the buttock).