Your hamstrings include 3 large muscles that run along the back of your thighs. They extend from your pelvis to the top of the bones of your lower leg. The hamstring muscles -- including the biceps femoris, semimembranosus and semitendinosus -- play an important role in activities such as walking, running and jumping. The hamstrings function to bend your knees and move your hips backward.
The main function of your hamstrings is to bend your knees. This movement is performed during daily activities such as walking, running, climbing stairs and jumping. Your hamstrings also help rotate your lower leg. Two hamstrings attached to the inside of your knee rotate your lower leg inward. The third hamstring, attached to the outer border of your knee, rotates your lower leg outward. These movements fine-tune the position of your lower legs as you walk. Your hamstrings also function like brakes on a car to slow the speed at which you swing your leg forward while kicking or running.
Your hamstrings perform hip extension -- backward movement of your thigh. Although the gluteal muscles in your buttocks are the main muscles that perform hip extension, your hamstrings assist with this motion as you move from sitting to standing, as well as with squatting and jumping. Hip extension performed by your hamstrings also helps propel your body forward as you run.
Reviewed by: Tina M. St. John, M.D.