Hamstrings may be the most commonly stretched muscle group ever, even if you barely use them. But if you want to have better hamstring flexibility this post may help you achieve maximum flexibility.
There are numerous ways of stretching; static, dynamic, ballistic and proprioception neuromuscular facilitation (or PNF for short, you may know them as partner stretches). Surprisingly, when assessed over a period of time, they all show similar increases in range of motion (how much you can move your leg). So this choice is entirely up to you, personally I’d go for the static stretch as they are least painful (personal opinion) and you can easily do them while watching TV or sitting down after your workout.
Whether you are sitting down, lying down or standing up, whether you are stretching in a straight leg raise fashion (image below) or a straighten your knee fashion, increases in ROM are similar. However, I would recommend doing both. You can think of it as stretching from both directions, straight leg raise you may feel higher up the hamstring closer to your bum. When you do the straighten the knee version, you may feel it more towards the knee. So doing both you stretch both ends of the muscle… or do you?
The straight leg version, you place a foot on a surface, and tilt forwards from your hips, imagine pushing your bum back and bringing your chest towards your knee. In the Straighten the knee fashion, start of in the same way but with a bent knee, then bring your chest close to your knee, now in this position, attempt to straighten your knee and there you will feel a stretch. Either by sliding the foot forward or moving your hips back.
Not only should we stretch with a bent knee and straight knee. But we should also stretch straight in front of us and to the side. This gets more of the parts of the hamstring, as you have three muscles making up the hamstring group, stretching in one direction will not get them all. Try it out and tell me you don’t feel a different part of your hamstring screaming out in stretch pain.