Now when we know where it sits and its function, it will be easy to understand the reasons why it tightens so easily. One main reason for its tightness is sitting for prolonged hours. While sitting the muscle is kept in shortened position, which results in its tightness overtime. Second postural reason is anterior pelvic tilt which forces lower back to arch more forward. Here, the hamstrings are loaded constantly to prevent excessive arching of the back. Other reasons for increased hamstring tension are previous muscle injuries, tendonosis and sciatic nerve tightness or irritation.
Stiff hamstrings are prone to injuries like muscle tear and tendinosis. It also affects pelvic positioning and reduces hip flexion which increases chances of having low back pain. It also increases its antagonist’s work’s muscle (quadriceps), which can lead to quadriceps muscle and knee injuries. So it is important to maintain good flexibility in the muscle.
Many of the times a good hamstring stretch is a false hamstring stretch. The feeling of stretch is similar and in fact sometimes stronger because it is the sciatic nerve which is getting stretched and not the muscle. A feel of stretch in the leg also suggests that sciatic nerve is being stretched. Simple way to target this issue is to bend the knee few degrees. By this the pull on sciatic nerve is reduced and hamstrings can be stretched properly.