The iliopsoas muscle is frequently regarded as a single muscle, because it is a blending of two muscles, the psoas major and the iliacus. The "psoas major" is a powerful flexor muscle of the thigh at the hip joint. If both psoas major muscles are fixed from below, they act as important flexors of the trunk on the hip, as in sitting up from a lying-down position. The "psoas minor" is a weak flexor of the trunk and the lumbar spinal column. It is supplied by a branch of the first lumbar nerve. The "iliacus" works with the psoas major as a powerful flexor of the thigh at the hip joint. It joins the psoas in a number of other actions as the "iliopsoas."
There's an old saying I found on the internett. And it goes like this. "Whosoever shall suffer low back pain will surely come to know the Psoas muscle. And lo, they will continue in their agony until it be made comfortable and true again". And so you ask, 'Just where is this Psoas, and how do I care for and nurture it?'
The Psoas is one of two major muscles that support and join the low back, pelvis and leg. It is connected to the sides of the last thoracic , and all five lumbar vertebrae and the substance between each vertebrae. It travels down into and through the pelvis. Here it joins with the 2nd major muscle, the Iliacus (Ilio), which lines the inside of the hips. Both muscles then leave the pelvis and attach to the inside of the leg at the Lesser Trochanter (a nub on the inside upper thigh bone).
Together, they are called the Ilio-psoas, a strong hip flexor (bringing the thigh toward the chest). Riders of bicycles and exercisers use their Ilio-psoas when 'peddling up'. The use of clips enhances this muscles action. Another good exercise is performing leg lifts while lying on the floor, keeping one leg flat and raising the other leg toward the chest.
I see many people suffering from back and neck injuries with acute or chronic pain. I find that low back problems from strain or vertebral misalignment are accompanied with tension and pain in the Psoas, and sometimes the Iliacus.
Muscles can relax when both of the attachments are placed near each other. To relax the Ilio-psoas, you can simply bring the knees up toward the chest while lying on your back. A good position is to lay on the floor on your back bringing the knees up, cross the ankles and hold them with your hands, allowing the knees to spread. Relax with deep breathing for one to two minutes. Repeat as often as you like. Water therapy or moist heat are good ideas. A therapist with the proper skills can also help alleviate this tension and pain.
So if you have suffered low back pain or injury and are between bouts, or you want to be preventative, sit ups with bent knees and leg lifts will go a long way in keeping you ridin' and smilin'.