Hamstring Anatomy

The hamstrings are made up of three muscles, semitendinosus, biceps - femoris and semimembranosus that run down the back of your upper thigh. Their main function is flexion of the leg at the knee joint - bringing your heel up towards your buttocks, and extension of the hip joint (taking your leg backwards), as well as assisting in turning the leg both inwards and outwards. 

Other muscles such as the those of your buttocks and adductors will also assist in these movements.

1 The buttocks (gluteus maximus)

2 The Biceps Femoris insertion, just below your knee joint, at the head of your fibula (smaller shin bone). It originates at the base of your pelvis (Ischial Tuberosity) and also at the rear mid-section of your thigh bone (femur). It's main function is to extend the hip, provide flexion of the knee joint, and aid in lateral rotation of the hip - taking your foot outwards.

3 Semimembranosus insertion, just below the knee joint, on the inner side of your shin bone (Tibia). It originates at the base of your pelvis (Ischial Tuberosity). It's main function is to extend the hip, provide flexion of the knee joint, and aid in medial rotation of the hip - taking your foot inwards.

4 Semitendinosus runs alongside Semimembranosus, with its origin in the same place, however its insertion is slightly lower on the Tibia. It's main function is to extend the hip, provide flexion of the knee joint, and aid in medial rotation of the hip - taking your foot inwards.