The iliopsoas is at the heart of the body’s core—which is exactly where many back problems can be traced to. A simple exercise and stretching program can help keep your athletes in the game.

By Gary Gray, Robert Dowling, and Vern Gambetta

Gary Gray, PT, is the Director of Gary Gray Physical Therapy, in Adrian, Mich. Robert Dowling, MPT, CSCS, is the Director of the Advanced Physical Therapy Clinic, in Heartland, Mich. Vern Gambetta, MA, is the President of Gambetta Sports Training Systems, in Sarasota, Fla., and a frequent contributor to Training & Conditioning.

Training & Conditioning, 10.9, December 2000,

Try to conjure up an image of the iliopsoas. Try to define its function. For most of us, a true understanding of the role this muscle plays in many common injuries and performance problems is elusive. To make matters worse, because it is not a visible muscle, like the lat, quads, or pecs, its role and contribution is often not fully appreciated until injury occurs.

But anatomically, the iliopsoas acts over several joints that are key to successful lower extremity and trunk function. Thus, it warrants special consideration in a multitude of problems, including those of the low back, sacroiliac, hip, knee, and shoulder. Our focus in this article is to look at the interaction of the iliopsoas with the low back, and to answer the question: What are the performance and possible injury implications stemming from the function of the psoas?

A Closer Look
The iliopsoas is formed by the combination of the terminal ends of two posterior abdominal wall muscles, psoas major and iliacus. This combination inserts into the lesser trochanter of the femur. The combined origin includes the T12-L5 vertebra, raphe of diaphragm, interval discs (psoas major portion), the iliac crest, iliac fossa, and ala of the sacrum (iliac portion). Innervation is provided by the ventral rami of the lumbar L1-3 and the femoral nerve.1,2

Traditional texts cite the primary function of the iliopsoas as the most powerful flexor of the hip during the swing phase of the gait cycle, and as a trunk flexor in stance phase.1,2,3 While the ability of the iliopsoas to perform these concentric actions is clear, little has been written of the necessity of the iliopsoas to function in other planes of movement and the ramifications of these functions in allowing normal activity. Further, the importance of synchronicity between left and right iliopsoas muscles and surrounding musculature is often overlooked. But, as we’ll see, an understanding of the neighboring hip, pelvic, and lumbar musculature is integral to any discussion of the function of the iliopsoas.

The function of the lower extremities in all activities can be summed up simply: to get the body to and from what it wants to do and to allow the body to do something worthwhile while it is there. Most of this functional activity occurs at a subconscious level. The body is constantly reacting and interacting with the environment in order to balance, bend, extend, shift, rotate, etc. This is described as a “chain reaction”2—a reaction of the entire kinetic chain in order to accomplish the functional goals desired. This chain reaction involves the integration of many components, foremost among them, muscles. And, the paramount muscle at the heart of the kinetic chain is the iliopsoas.

There are many ways to look at this chain reaction. It involves the gaining of stability in order to demonstrate mobility, or the absorbing of shock in order to utilize this energy to propel.

Put another way, there is a component of pronation that occurs in order for the system to effectively supinate. This does not refer to the specific pronation or supination of the feet—pronation and supination occur at all joints and in all phases of motion within the lower extremity, pelvis, and trunk, as well as the upper extremities.

As the lower extremities—and, by extension, the pelvis and trunk—contact the ground during the initiation of the stance phase, there is a collapsing of the whole kinetic chain, which is termed pronation. Pronation occurs as shock is absorbed. It occurs because of the effects of gravity and ground-reaction forces as well as momentum.

The re-girding and stabilization of the lower extremities, pelvis, and trunk in order to propel the body forward is termed supination. Supination is the productive force of propulsion. It is a reaction to the loading occurring during pronation.

Basically, pronation succumbs to gravity and supination takes advantage of, and ultimately overcomes, gravity. The cycle of pronation and supination causes the muscles to react in a certain way and allows them to act upon the system to allow it to successfully move. The transformation of pronation into supination is the key to success of the system during all activities, no matter how simple or complex.

Pelvic Motion
The pelvis moves in relation to the low back and hip. It also moves in a rhythmic fashion through space as it reacts to pronation and supination. At the initiation of the stance phase, one hip is flexing, adducting, and internally rotating, while the opposite hip is extending, abducting, and externally rotating. At the same time, the pelvis and lumbar spine are also interacting with both of these components of motion.

The iliopsoas is stimulated to interact with these motions and forces in all three planes. Besides dealing with what the hip is doing, the iliopsoas deals with the reaction of the pelvis and the lumbar spine. During pronation, the pelvis will anteriorly rotate in the sagittal plane, rotate internally in the transverse plane, and translate laterally while elevating on the side that is pronating. These movements are driven by gravity, ground-reaction forces, and momentum, as well as the forces created by other muscles and the opposite-side iliopsoas. They occur in reverse during supination.

The timing of these motions is the key to effective movement regardless of the sport demand. If the timing is off, the psoas does not lengthen in all three planes. If the hip does not extend properly in the sagittal plane, does not rotate properly in the transverse plane, or does not move in the frontal plane, the stress is transferred to the back. The back is not designed to withstand those stresses. To put it in simplest terms, the back has its own job to do, it does not need to also do someone else’s job. If the pattern persists, eventually, injury will occur.

In addition, weaknesses of the abdominal obliques and/or the gluteals places the pelvis in an anteriorly rotated position. In this position, the psoas is shortened and remains tonic. By virtue of its upper (lumbar) attachments, the increased tone and tightness of the psoas increases the lumbar lordosis and further increases the load on the low back.

Iliopsoas Function
The function of the iliopsoas is no different than any other muscle in the locomotor system. It initially reacts and is stimulated during pronation through a lengthening (eccentric) contraction. It receives its greatest stimulation during the stance phase in the transverse plane. Because of its attachment to the lesser trochanter, the iliopsoas becomes stimulated in the transverse plane by decelerating internal rotation of the femur relative to the pelvis and the lumbar spine.

The iliopsoas pronates in the frontal plane as the body moves laterally over the fixed foot, by lengthening in the frontal plane. Interestingly, during this time, the hip is actually flexing, which produces no eccentric stimulation to the iliopsoas in the sagittal plane. As the body progresses over the fixed foot during midstance, however, the iliopsoas receives stimulation as it begins to react to the extension of the hip. Thus, during pronation, the iliopsoas is shortened in the sagittal plane until midstance, and functions primarily in the frontal and transverse planes prior to midstance.

During supination, the iliopsoas facilitates external rotation of the hip as well as translating the pelvis to the opposite side. It finally builds up a significant amount of eccentric tension prior to a heel lift in order to prepare for the sagittal-plane hip flexion during the swing phase.

Because the iliopsoas functions in all three planes of motion and in relation to its contralateral partner, all three planes of motion must be taken into consideration when analyzing this muscle. All of the other muscles of the kinetic chain are dependent upon the function of the iliopsoas, just as the iliopsoas, in return, is dependent upon the successful function of all of the other muscles.

Performance Implications
The psoas is a much bigger player in the gait cycle than most people ever imagine; therefore, it requires our attention when designing performance—as well as rehabilitation—programs. The psoas is a vital connector. But strength is not the issue. Functional flexibility is what is most important. We must do everything possible to maintain proper lengthening in order to ensure the muscle is able to function properly.

There are numerous clinical ramifications regarding the iliopsoas, especially given its function in all three planes and synergy with other muscles of the locomotor system. With any appreciation of the iliopsoas’ function in the transverse and frontal planes, its involvement in iliotibial band syndrome, piriformis syndrome, and patellofemoral dysfunction can be assessed and an appropriate exercise program can be designed.

Traditionally, the iliopsoas has been tested for length only in the sagittal plane via a Thomas test. But, as we have seen, the psoas functions in all three planes; therefore, we must assess it in all three planes. More functional tests for psoas function are the posterior reach test and posterior lateral reach test. These tests are done with the athlete in a weight-bearing position, which will give a better functional picture of any limitations. It is also important to stress that, with these tests, we are looking for intra-individual differences. We are not trying to compare one subject to another, but to compare the right side to the left.

Our lifestyles, as well as many of the training modalities that we utilize, contribute to psoas dysfunction. We must recognize these activities and do everything we can to eliminate or modify them. Sitting, which student-athletes do all day before they go to practice, shortens the psoas. Long bus rides or airplane rides before a competition can cause problems of the psoas if the muscle is not properly stretched before starting competition. Stationary biking in a seated position, which is extensively used for conditioning, also shortens the psoas, as do stair-stepping machines. It is also advisable to avoid from trunk-flexion movement with the feet anchored, such as roman chair sit-ups.

The solution is to include in each athlete’s program a good psoas stretch that lengthens the muscle. This simple stretch should be done periodically throughout a training session to maintain proper length. For someone who sits a lot, this stretch should be done at least once an hour. This will go a long way to preventing many of the common low back problems that result from shortening of the psoas.

1. Gray G: Chain Reaction. Adrian Wynn Marketing: Adrian, Mich., 1993.

2. Moore K: Clinically Oriented Anatomy, second ed. Williams and Wilkins: Baltimore, 1985.

3. Warfel J: The Extremities Muscles and Motor Points, fifth ed. Lea and Febiger: Philadelphia, 1985.