What Is the Purpose & Function of the Hamstring?

People refer to their hamstrings as being tight or weak, but what exactly does this mean? You probably talk about these muscles all the time, but you may not fully understand where they are or what they do.

What Is the Purpose & Function of the Hamstring? (Image: jacoblund/iStock/GettyImages)

The hamstrings include three 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.

Knee Function

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.

Hip Function

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.

Strengthening and Stretching the Hamstrings

Exercises that strengthen the hamstrings include the leg curl machine, dead lifts and supine leg curls using a stability ball. To do the supine leg curl, lie on your back with your feet on a stability ball; lift your hips and bend your knees to roll the ball toward your buttocks. Pause for a count and release to the starting position.

Forward bends stretch the hamstrings. Perform these seated or standing. Only stretch to the point of slight sensation. If you feel the muscles pulling or strained, you've likely gone too far and risk injury. Hold a hamstring stretch for 20 to 30 seconds; never bounce as this too can make the hamstrings prone to injury.

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