The hip flexors are comprised of your psoas major, psoas minor, and iliacus muscles. The psoas muscle in particular is one of the most commonly used muscles in the body yet most people have never heard of it.
The main role of the psoas muscle is to flex (or bend) the hip. For example, when doing a situp that brings the your body (including the lower back) away from the ground and towards the front of the thigh / leg, the hip flexors will flex the spine upon the pelvis. The importance of this muscle is due to the frontal attachment on the vertebrae, rotation of the spine will stretch the psoas.
Tightness of the psoas can result in lower back pain by compressing the lumbar discs. When you compound that with a sedentary lifestyle this forces the muscle become even stuck in a shortened / tight position. It will cause low back pain, anterior hip pain, restrict hip extension, and even loss of feeling in the anterior thigh do to the femoral nerve piercing the posas muscle. When this muscle is stuck in a shortened position to often it will cause your lower spine to be pulled forward creating irritation of the posterior spine joints. To maintain good hip function, flexibility, and low back neutrality in an upright position it is key to maintain a healthy and lengthened psoas. Usually stretching this muscle will not completely resolve this problem in and of itself. But maintain good psoas length is vastly important. Below you will find directions to a hip flexor stretch that I prescribe to all my patients that have any of the above listed issues.
Hip flexor stretch
Stand two feet back from step or chair
1. Place Right foot on step
2. Keep trunk upright and pelvis facing forward
3. Bring body weight forward while bending L knee slightly and allowing heel to lift (will be stretching the left
4. hip flexor if right leg is elevated).
5. As you come forward, lift left arm reaching diagonally.
6. Reach arm forward in 9 spots as if there was a tic-toe box making sure to reach arm toward each box.