Hip Flexor Stretch
The primary muscle group of the hip flexors is the iliopsoas, comprised of two muscles (iliacus and psoas) which originates in two areas (top of pelvis and lumbar spine) and attaches in the groin area. Since this muscle both connects to the spine as well as to the top of the pelvis which can pull on the spine, keeping this muscle stretch out can help prevent and improve back pain. It may become shortened (could cause discomfort in the front of the hip) with too much time spent sitting down, driving, sleeping with the head of the bed up, and a posture with a sway back. It may cause back pain when it gets stretched out in repetitive movements such as walking or running. Injuries can occur with climbing or sprinting. Click on the link below to watch a demonstration of how to stretch the hip flexors.
If you need a better stretch, simply rotate your shoulders or sidebend your body in the direction of the muscle that is being stretched, like the photo above.