Hip flexors, in the human anatomy, refer to a cluster of skeletal muscles that help to pull the knee forward, by flexing the femur or the thighbone onto the lumbo-pelvic complex. Together called iliopsoas, or the muscles of the inner hip, they consist of Psoas major, Psoas minor and Iliacus muscle. The hip flexor group of muscles, located in the abdomen and the thigh, are active when you stand up from a sitting position, or when you dance, climb stairs, run, play soccer or even when you do resistance training. Allowing the up and down movements of your legs and at the same time working to balance your spine's stability, they represent the strongest muscles in your body.
The problem, however, is that a sedentary lifestyle of sitting most of the time tends to allow the hip flexor muscles to shorten, propagating in its wake, problems that go all the way from our back to our feet. Old age or sleeping in a fetal position will also hasten the flexor shortening process.
Lack of flexibility and not strength hampers the smooth functioning of the hip flexors. Imagine someone with a broken arm in a plaster for 8 weeks. On removing the plaster, he will find he is not able to flex and stretch as usual. This is because your muscles, over this period of inactivity, have shortened, and then it takes long hours of physiotherapy, before he regains his original flexibility. It is the same with the hips and if not flexed regularly, or if you consign yourself to a sitting position for long hours, you are inviting problems with your hip flexor muscles, resulting in limiting your hip movements.
When the hip flexor muscles lose their flexibility and become tight, the back gets compressed by virtue of the pelvis thrusting forward, and standing in this position requires one to over-arch his back. The experts commonly refer to this as swayback and anatomically, as Hyperextension. Standing or sitting in this position for a long time mounts pressure on the joints and the lower spine, leading to painful arthritis in due course.
To rectify the situation, you can undertake a lot of exercises, but the most important is warming up the flexors with moderate stretches, especially lunges, bending one knee at the front, and stretching the other leg straight behind. They also recommend using a foam roller 24 inches long and 6 inches in diameter, to roll between the knees and the hips, while lying face down with your elbows for support.