The problem is that these muscles aren't designed to be prime movers—they're designed to support the action of the glutes. Inability of activating the glutes can result in low back pain (low back muscles compensating), hamstring strains (overacting hamstrings), hip pain (resulting from hamstring-dominant hip extension) and knee pain (poor glute medius strength).
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..
If most inner-thigh openers feel too easy (and your ankles and knees are injury-free), try Frog Pose. Get down on all fours, with palms on the floor and your knees on blankets or a mat (roll your mat lengthwise, like a tortilla, and place it under your knees for more comfort). Slowly widen your knees until you feel a comfortable stretch in your inner thighs, keeping the inside of each calf and foot in contact with the floor. Make sure to keep your ankles in line with your knees. Lower down to your forearms. Stay here for at least 30 seconds.
Meanwhile, it’s extremely common for non-life-threatening low back pain to be alarmingly severe and persistent — to have a loud bark! Your doctor may not appreciate how true this is, and may over-react to all persistent low back pain, even without other red flags. In most cases, you shouldn’t let them scare you. Being “freaked out” about persistent back pain is the real threat: it can make low back pain much worse, and much more likely to last even longer (a tragic irony).
Why does it tighten down so much when overworking as a spinal stabilizer? Remember that length tension relationship we talked about? Well, if the psoas is tight, it can compress the spine easier, thus providing spinal stability. Plus, it has to work a lot to stabilize the spine. When you don’t have correct functioning of the diaphragm and abdominals, the psoas holds a great deal of tension to do the job. This tightness or tension makes it a very ineffective hip flexor.
Work on strengthening all of your core muscles and glutes. These muscles work together to give you balance and stability and to help you move through the activities involved in daily living, as well as exercise and sports. When one set of these muscles is weak or tight, it can cause injury or pain in another, so make sure you pay equal attention to all of them.