Health and fitness for life.

Ever get the instruction "move from your psoas" in your dance class? The psoas (pronounced SO-az), a revered but misunderstood muscle hidden away deep within the pelvis, receives one of the most frequent references in dance training. So where is your psoas and how can it work for you?

"Psoas" is a Greek word, like many anatomy terms, which literally means "muscle of the loin." It technically has a major and a minor part that work along with its companion muscle, the iliacus. Together they are called the iliopsoas, and they comprise the deep hip flexors. The iliopsoas runs in your abdomen behind the organs, along the front of the spine, and ends at a point in the inner leg called the lesser trochanter. A great visual image used by yoga guru Rodney Yee describes the psoas as lying on the front of the spine like a long lizard basking in the warm sun over the big desert rock of the lumbar spine. The iliacus component runs along the inner part of the wide bone of the pelvis.

There is a psoas muscle on each side of the pelvis so that you can use one alone or use them in concert. The same is true for the iliacus muscle. In standing, using one side creates a hinge at the hip (if you hold the waist steady) and moves the thigh upward toward your nose, while using both sides hinges the entire trunk forward.

To help you get an even better grip on the geography of the muscles, look at the other hip flexor muscles. There are superficial (meaning closer to the surface) hip flexors called the quadriceps on the front of the thigh. What distinguishes the deep from the superficial flexors (recall that flexors bend the body forward) is the spinal connection of the deep ones. Think of it this way: The deep hip flexors are located in the abdomen and pelvis and end high up in the thigh, so they cover both the spine and the hip. The superficial hip flexors attach to the bony front of the pelvis and end either in the thigh or with the kneecap tendons. Together, the deep and superficial muscles form a long biomechanical chain from the torso to the leg. This is why teachers often tell you to move your legs from your waist. Also, when we talk about "extensions" to the front or side, what we really mean is to flex the hip with the deep hip flexors and then extend the knee with the quadriceps.

Dance training is keen to make this distinction because we all value the beauty of high legs; only by using the psoas can we flex the thigh upward past the ninety-degree range. Noisy hips can indicate a problem. Many dancers' hips can be heard to pop spontaneously during the course of a regular warm-up. However, snapping and thunking hips are usually the sign of unbalanced or uncontrolled musculature around the hip. According to Dr. Carol Teitz, an orthopedic surgeon at the University of Washington, usually only one side is affected: the preferred or most frequently used gesturing side. Choreography is asymmetrical, and often dancers' movements are selected based on what looks best--usually their preferred sides. If an extension is higher on one side than the other, it's a sure bet the choreographer will use that side.

The iliopsoas is crucial for both centering body weight through the pelvis without overextending the low back and allowing better control while flexing the hip. This is why the command to drop the tailbone is often given. If the hip noise is allowed to continue repeatedly without correction, the result could be a painful and irritated iliopsoas mechanism, or tendinitis. One way to tell if this is happening to you is to do a straight-legged sit-up with your feet held down. If you get pain in your hip, you might want to seek medical advice.

In order to train the psoas complex, try this floor exercise called "toe touching." Lie on your back, bend your knees, and let the spine go heavy into the floor, imprinting the vertebrae into the ground. Exhale and curl your upper body up as in an abdominal crunch position, softly reaching your arms out parallel to the floor. Inhale, then exhale again and flex at the hip, lifting one leg, then the other, gently unweighting the legs by imagining they're levitating off the ground. Then point your toes and alternate touching the big toes to the floor until you complete sixteen alternations. Be sure to keep your pelvis centered with as little side-to-side shifting as possible. To end, relax the feet down and breathe into your pelvis for three breath cycles.

Suzanne Martin maintains a private practice in physical therapy and Pilates, is the lead physical therapist for Smuin Ballet, and conducts nutrition seminars at San Francisco Ballet School.