Located deep in the front of the hip and connecting the leg, pelvis, and abdomen, the hip flexors— surprise, surprise— flex the hip. But despite being some of the most powerful muscles in our bodies (with a clearly important role), it’s easy to neglect our poor hip flexors— often without even knowing it. It turns out just working at a desk all day (guilty!) can really weaken hip flexors since they tend to shorten up while in a seated position. This tightness disrupts good posture and is a common cause of lower back pain. Weakened hip flexors can also increase the risk of foot, ankle, and knee injuries (especially among runners) Hip muscle weakness and overuse injuries in recreational runners. Niemuth, P.E., Johnson, R.J., Myers, M.J., et al. Rocky Mountain University of Health Professions, Provo, VT. Clinical Journal of Sport Medicine, 2005 Jan; 15 (1): 14-21.. So be sure to get up, stand up every hour or so! And giving the hip flexors some extra attention is not just about injury prevention. Adding power to workouts, working toward greater flexibility, and getting speedier while running is also, as they say, all in the hips The effect of walking speed on muscle function and mechanical energetics. Neptune, R.R., Sasaki, K., and Kautz, S.A. Department of Mechanical Engineering, The University of Texas, Austin, TX. Gait & Posture, 2008 Jul; 28 (1): 135-43..
Avascular necrosis (also called osteonecrosis). This condition happens when blood flow to the hip bone slows and the bone tissue dies. Although it can affect other bones, avascular necrosis most often happens in the hip. It can be caused by a hip fracture or dislocation, or from the long-term use of high-dose steroids (such as prednisone), among other causes.
Here is how you do the hip rotation stretch: Sit on the floor with your knee out straight. Cross one leg over the other by placing your ankle on top of your knee (as if crossing your legs while sitting). Gently pull your knee across your body, and hold for five seconds. Then gently push the knee of the top leg away from you until a stretch is felt in your hip. Hold this position for five seconds, then slowly release. Repeat 10 times.
These exercises can be done three to five times per week; be sure to build in a rest day here or there to allow your hip muscles to recover. Working to strengthen your knees and ankles can be done as well to be sure you completely work all muscles groups of your lower extremities. Remember, your ankle and knee muscles help control the position of your hips, just as your hip muscles control the position of your knees and ankles. They all work together in a kinetic chain.
The side of the pain on its own doesn’t tell us much, and most of the one-sided sources of pain are viscera that usually cause abdominal pain instead of back pain, or in addition to it. In other words, the only reason to worry about right or left lower back pain is if it is otherwise worrisome: if you have other red flags or significant non-back symptoms.

Arthritis: The spondyloarthropathies are inflammatory types of arthritis that can affect the lower back and sacroiliac joints. Examples of spondyloarthropathies include reactive arthritis (Reiter's disease), ankylosing spondylitis, psoriatic arthritis, and the arthritis of inflammatory bowel disease. Each of these diseases can lead to low back pain and stiffness, which is typically worse in the morning. These conditions usually begin in the second and third decades of life. They are treated with medications directed toward decreasing the inflammation. Newer biologic medications have been greatly successful in both quieting the disease and stopping its progression.

Low back pain (LBP) is a common disorder involving the muscles, nerves, and bones of the back.[4] Pain can vary from a dull constant ache to a sudden sharp feeling.[4] Low back pain may be classified by duration as acute (pain lasting less than 6 weeks), sub-chronic (6 to 12 weeks), or chronic (more than 12 weeks).[3] The condition may be further classified by the underlying cause as either mechanical, non-mechanical, or referred pain.[5] The symptoms of low back pain usually improve within a few weeks from the time they start, with 40–90% of people completely better by six weeks.[2]