Tight hamstrings will pull on the ischial tuberosities, one of the areas of your pubic bone. This tends to tilt your pelvis back. Joints adjacent to this move in what’s called a “coupled” fashion, so when the pelvis tilts back the vertebrae in your lower back flex forward.
It can strain the ligaments that surround your vertebrae and also make bulging disks in your back worse. So, lengthening your hamstrings is key to moving your body as it is intended to and not putting unnecessary stress on your spine.
When your hamstrings are relaxed it allows your pelvis to tilt forward. The lumbar spine will then couple this movement in the direction of the extension which takes the strain off the ligaments and disks. The following stretches can gradually lengthen and reduce tension in the hamstring muscle, and in turn reduce stress felt in the lower back.