Many people have short hamstrings, the main muscle group in the back of the thigh which bend the knee and extend the hip. Shortened hamstrings are more common in men. Spending a lot of time sitting may be a contributing factor. Another factor is sitting with your pelvis tilted back and knees bent. This posture results in a loss of the lumbar lordosis, the natural arch of the lower back. It not only places strain on the joints, discs and muscles of your lower back but it also puts the hamstrings in a shortened position.
Shortened hamstrings make it more difficult to bend and lift things safely, because they limit the forward tilt of the pelvis. Some people believe they have short hamstrings because these muscles feel tight, however tightness is a sensation, not an actual limitation in mobility. It is possible to over-stretch the hamstrings, which can result in reduced pelvic stability, so if in doubt get advice from your health professional.
The Straight Leg Raise test is a quick test that can be performed by your Physiotherapist to determine whether your hamstrings are a functional length. Most people need 80 to 100 degrees of hip flexion, which allows you to sit on the floor with legs long and still keep your back fairly straight. If your hamstrings are tight but not short, you may be better to massage on a long foam roller rather than stretching them.
The Feldenkrais Method offers many creative ways to lengthen the hamstrings without straining the lower back. This gentle method helps you reduce excess tension in the muscles without the need for passive stretching.