I don't understand??
1. Your Gluteus Maximus is the biggest muscle in your buttocks area. Although this muscle has many roles in running it is involved in extending your leg through the swinging phase. When the muscle is not firing properly or inhibited, your leg will not extend to a full range of motion it is capable of. Inhibited simply is a term used to describe a muscle which is weak not due to pain or neurological cause.
2. A second muscle involved in this type of faulty running behaviour is the Psoas muscle. This is a muscle which crosses the front of the hip joint. While running the Psoas is involved in flexing the hip forward. Needless to say the Gluteus Maximus and Psoas are contently battling against one another as you run. One helps bring your leg forward as the other brings it back..over and over again.
3. Putting it all together - This combination of a weak Glut Max and a tight Psoas muscle will lead a runner towards a compensating gait. Now your back is exposed to extra forces it does not need on a consistent basis.
Its important when running to allow most of the movement to occur from your hips and allow the back to stay neutral. By creating this running technique back pain may be prevented and decreased significantly.
How do I know I have this problem?
Well any type of back pain should be addressed by a trained professional. This is because there can be multiple causes for the pain. It is important to rule out a serious pathology. However, there are ways to see if you have this particular problem. You may need a partner or again someone trained to observe different movement patterns.
1) Your gait - Sometimes this subtle hiking of your back can be seen from a partner while watching you run from a side view. Videotaping patients while running on a treadmill is a great learning tool to use as well.
2) The tight Psoas - You may just feel the tightness in general but can still use different test to see if it is tight.
On a gym bench or table lye on your back with your buttock at the end of the table. Allow your legs to hang off the bench freely. With your hands take one leg and bring your knee towards the chest. If the opposite leg comes off the table almost immediately or in an excessive range this can indicate a tight Psoas. This same test is often used by manual therapist and is called the Modified Thomas test.
LIEBENSON, C. (2007). Hip dysfunction and back pain Journal of Bodywork and Movement Therapies, 11 (2), 111-115 DOI: 10.1016/j.jbmt.2007.01.005