Hamstrings

Three muscles form the hamstring group and cover the entire back of the upper leg. The semitendinosus and semimembranosus extend down the inner side and the biceps femoris lies on the outer side. The ischial tuberosity, or seat bone (lower side bone of pelvis), is the point of origin. This can be felt as hard bumps in the centre of the fleshy glutei (seat muscles) while sitting. Biceps femoris and semitendinosus are joined by a common tendon on the bone but semimembranosus is attached separately Semitendinosus has a very long tendon but semimembranosus lies underneath and is fleshier. Biceps femoris spreads downwards and is directed diagonally outwards and attached by its tendon to the outer part of the knee and top of fibula. The picture (left) is of the right leg viewed from behind. It is almost opposite in placement and direction to sartorius at the front of the thigh. The other two hamstrings are fixed onto the inner side of the knee at the back of the top of the shin bone (tibia). Sitting with knees bent allows the cords of the hamstring insertion tendons to be felt just above the back of the knee.

Tensing the hamstring muscles by trying to push you foot backwards against a chair leg (isometric) allows the semitendinosus tendon to be felt and runs halfway up the inner side of the back of the thigh. The biceps femoris tendon is equally prominent on the outer side of the back of the knee whereas semimembranosus is not so near the skin surface. It can still be felt just under the semitendinosus tendon at the inner side of the knee. The three hamstrings act on the hip and knee joints and while standing or lying face downwards they help the glutei to take the leg backwards from the hip. The hamstrings and glutei work to straighten the body from a forward bending position at the hips. While lying face downwards, the hamstrings bend the knee joint to raise the lower leg upwards against gravity and control lowering in the direction of gravity.

The hamstrings are relatively inelastic compared to the other major muscles because of the long taut cord-like tendons. Difficulty is usually experienced while trying to touch the toes. A common injury to the hamstrings occurs if it is not flexible or long enough to stretch at speed when a powerful and rapid knee extension occurs. The hamstring can easily be overstretched with consequential muscle tears. This is quite common in footballers - fast knee extension to maximise speed and power when kicking (kinetic energy = 1/2mv2) and untrained track athletes - the explosive push from starting blocks.