What is the job of the hip flexors?

The hip flexors are a group of muscles located at the front (anterior) of the hip joint. As the name suggests their job is to bring about flexion of the hip, raising the thigh as in bringing knees to chest.

Why do hip flexors tighten?

Tight hip flexors can have several causes but most commonly its due to being sat for long periods of time behind a desk for example or driving for hours on end.
Also not stretching out or poor positioning during exercise can also have an effect. When the muscles spend a long time or are repetatively trained in a restricted (shortened) state then the muscle will develop in that way which will reduce the range of movement (ROM)

Why can tight hip flexors lead to back pain?

The answer lies in the pelvis. When the hip flexors are tight they pull the front of the pelvis down. This brings the pelvis out of its neutral position and creates what is known as Anterior Pelvic Tilt. When the pelvis is tilted the lower vertabrae have to realign to cope with this, so the curve (lordosis) in the lumbar region of the spine increases. With this change of position the lower back muscles are shorten and the disc spaces are reduced, this puts more pressure on the spine as it is now not in normal function. So the spine and back muscles have to work harder and are in turn tightened which can lead to back pain.

How do we combat tight hip flexors?

Through appropriate stretches and exercises that will lengthen the muscles as well as strengthen them at the same time.