The hamstrings are a group of muscles made up of the biceps femoris, the semitendinosus and the semimembranosus muscles. The primary job of this muscle group is to bend your knee, but it also assists in extending your hip and rotating your leg inward and outward. The hamstrings are used every time you walk, run, jump, get out of a chair, squat or climb stairs.
It is important to keep your hamstrings both long and strong to avoid injury to the hamstrings or excessive strain on your back. Try the following two exercises to maintain a good balance between the strength and the length of your hamstrings.

1. Hamstring Stretch: Lay on your back and loop a strap around your ankle. Keep your knee straight as you pull your leg upward. Pull until you feel a strong but comfortable stretch behind your thigh and hold for 30 seconds. Do this 4 times then switch to the other leg.

2. Standing Hamstring Curl: Stand with a band under one foot and looped around the other ankle. Bend your knee to pull up against the resistance. Slowly lower and repeat 10 times. Perform 2 sets of 10 on each leg.