The hamstrings are large, long muscles located on the back of the thigh.
While it has long been known that stretching any muscle is important to keeping it flexible, studies have now shown that static stretching is better for the hamstrings.
Especially if you have previously injured your hamstring and have recovered, but still find your hamstrings are stiff and not as flexible as you would like.
There are essentially two types of stretching: static, and dynamic or ballistic. Static stretching involves holding a position, while dynamic stretching involves bouncing, swinging or pulsing movements.
Generally speaking, static stretching involves less risk of injury. You should begin any exercise session with some gentle activity to begin to warm up your muscles. Then you can move on to stretching and your desired activity. Cool down by stretching again. [Stretching Exercise]
To stretch your hamstrings, sit on a firm surface with your legs out in front of you. Keeping one leg straight, bend the other leg at the knee, placing the sole of your foot against the inside of the leg that is remaining straight. [Hamstring Stretches]
Pull yourself up and lean forward toward the foot of your straightened leg until you feel a stretch in your hamstring. Keep the straightened leg relaxed, and point your toes up. Hold the stretch for 30 seconds, then slowly release, and repeat with the other leg.
Remember you want to feel the stretch working, but you should never stretch to the point of pain. Also, do not stretch cold muscles; always warm up first.