Anatomy of the Hamstring Muscles
The hamstrings are a group of muscles and their tendons at the rear of the upper leg. They include the biceps femoris, semitendinosus, and semimembranosus. The hamstrings flex the knee joint and extend the thigh to the back side of the body. They are used in walking, running, and many other physical activities.
The hamstring muscles have their origin, where their tendons attach to bone, at the ischial tuberosity of the hip (often called the sitting bones) at one end and the linea aspera of the femur at the other. The hamstring tendons flank the space behind the knee.
The most medial muscle, the semimembranosus, inserts on the medial condyle of the tibia bone. The semitendinosus inserts on the superior part of the medial tibia. The most lateral hamstring, the biceps femoris, inserts on the lateral side of the fibula and also attaches to the superior part of the lateral tibia. They are innervated by the sciatic nerve.1
What Do the Hamstrings Do?
You use the hamstrings for walking, running, and jumping. They flex the knee and extend the hip at the beginning of each step.1 In walking and running, they are antagonists to the quadriceps muscles in the action of deceleration of knee extension.
Because the hamstrings have their origin at the sitting bones, they are stretched while sitting, and long periods of sitting may affect their function.
Walking, running, and climbing and descending stairs builds the functional fitness of the hamstrings. This can be important cross-training for people whose primary exercise is bicycling, which targets the quadriceps. Overdevelopment of the quadriceps needs to be balanced with exercising the hamstrings.
Isolation and compound exercises for the hamstrings may be used for rehabilitation or bodybuilding. Exercises that involve knee flexion and hip extension are used to build the hamstring muscles.3
Hamstring flexibility is important for runners and may help prevent injury and delayed onset muscle soreness after exercise. Tight hamstrings may also be felt as limited motion when straightening the knee or a cramp at the back of the knee. Hamstring stretches are a common part of a stretching and flexibility routine.
The hamstrings take a beating during sports such as soccer, football, basketball and tennis, where running is combined with rapid starts and stops. Hamstring sprains and tears are common. Worse hamstring injuries are evident when there is significant bruising behind the thigh. Repetitive stress injuries from running or walking might also be the cause of hamstring pain.