"Do you know where your piriformis is?" Over the years I've gotten a variety of responses to this question: sometimes a blank stare, sometimes a laugh. Once in a blue moon, someone correctly points to the back of the hip.
If the location of the piriformis is a mystery to most yoga students, its action and its function in yoga poses are even more mysterious. Most students have no idea of the important work it performs. Unfortunately, the piriformis is best known for the problems it causes, including sciatica. But this obscure muscle is crucial in stabilizing the pelvis and knees.
Before we examine the action of the piriformis, let's clarify its whereabouts. It's located deep in the buttock, underneath the better-known gluteus maximus. The piriformis is part of a group of six muscles called the deep external hip rotators. These six muscles all originate at various locations on the back of the pelvis and cross the back of the hip to insert on the greater trochanter, a protuberance on the outer upper femur (thighbone) about six to eight inches below your waist. The position of the rotators, reaching from the back of the pelvis to the outer thigh, gives them excellent leverage to externally rotate the hips—in other words, to turn the legs outward.
Perhaps you've made the acquaintance of your rotators during a massage, when deep work on the back of a buttock brought your awareness to tight and tender muscles. That tenderness, which can range from minor soreness to sharp pain, may be due to overworked, strained, or chronically tight rotators. In such cases, massage, gentle stretching, and a reconditioning exercise program will help solve the problem. Poses that can help stretch a chronically tight piriformis include preparations for Eka Pada Rajakapotasana (One-Legged Pigeon Pose), the leg position of Gomukhasana (Cow Face Pose), and Ardha Matsyendrasana (Half Lord of the Fishes Pose).
However, the piriformis and its brother rotators sometimes get blamed for problems they didn't cause. The buttock is a common area for referred pain from lower back problems, including arthritis, disc injuries, and sacroiliac problems. So it's very important that any persistent hip pain be thoroughly evaluated by your health-care providers before you decide on a course of treatment.
While the piriformis and the other deep hip rotators are best known for the problems they create when they're tight, they do need to be strong to perform important functions in yoga poses. They help to stabilize the pelvis and knees when you bear weight on the legs, especially in standing poses. To experience this, stand with your legs wide, preparing for Virabhadrasana II (Warrior Pose II). Turn your right foot out 90 degrees and your left foot slightly in. Notice that even though the right foot is turned out, there is a tendency for the knee to turn in.
This internal rotation of the femur is due to the pull of the internal rotators of the hip, including the adductors (a large muscle group of the inner thigh) and the medial hamstrings on the back of the inner thigh. If the foot and shin rotate out while the femur rotates relatively in, the knee twists, putting a potentially damaging strain on its ligaments. A contraction of the external rotators is needed to bring the knee into alignment with the foot to protect the integrity of the knee joint.
To refine and strengthen this action, try practicing Warrior II with your back to a wall. Stand close enough so your right buttock touches the wall but your feet do not. Turn your right foot out so the foot is parallel to the wall, and turn your left foot in slightly more than perpendicular to the wall. Now come down into the pose, bending your right knee and keeping your left leg straight and strong. Place a yoga block or firmly rolled towel between your right knee and the wall, and press your right knee into this prop. It is the deep hip rotators that are putting pressure on the block—and at the same time aligning your knee perfectly with your foot.
As you press the right knee toward the wall, make sure that you don't let the left thigh buckle away from it. In fact, if you'd like to increase the challenge, place a second block or rolled sticky mat between the wall and the center of your left femur; hold it in place by firmly pressing your left leg back while continuing to press the right knee into its prop. You will feel a strong action in the back of both hips as the piriformis and its friends externally rotate both legs. A similar action should occur in Parsvakonasana (Extended Side Angle Pose) to the right: Keep the right knee pressing into the right arm while maintaining a straight line through the left leg.
The knee is also at risk of being twisted in some straight-leg standing poses, and a strong contraction of the deep hip rotators is required to align the femur, knee, and foot. While in Trikonasana (Triangle Pose) to the right, turn your head and look at your right knee. Chances are, it's slightly internally rotated.
Now feel the firmness in your right buttock as you externally rotate the thigh to align the knee with the foot. (Notice that this action also creates a beautiful arch in your foot.) Even more challenging, maintain this alignment as you bend your knee and prepare to transition to Ardha Chandrasana (Half Moon Pose). In this transition, the rotators must act strongly to prevent the knee from angling in toward the big toe, and they must continue to contract as the knee straightens fully in the pose.
Let's look at one more straight-leg standing pose, Tadasana (Mountain Pose). Many people tend to stand with their feet pointing out slightly. Sometimes this may be caused by short and tight rotators that externally rotate the whole leg. If that is the case, the knees will also be pointing out, and you need to spend more time stretching the backs of your hips.
However, it's also fairly common for the feet to point out while the knees point in, an alignment that can contribute to pronation of the feet (collapsed arches), knee problems, and low back pain. Weak rotators can be the culprit behind this pathological alignment. If the external rotators aren't strong enough, the internal rotators (which include the gluteus medius and tensor fascia lata on the outer hip as well as the adductors) will pull the femur into internal rotation. In an attempt to align the femur, the outer hamstring, which is also an external rotator, takes over for the deep hip rotators. Unfortunately, the outer hamstring inserts into the lower leg, and so, instead of aligning the shin and thigh, it turns the lower leg out even more deeply, exacerbating the misalignment.
If you are dealing with pronated feet, knee problems, or lower back pain, be sure to take a few moments to stand in front of a mirror and look at your leg alignment. If your kneecap points over or even inside your big toe, weakness in your external rotators may be contributing to your problems. While work with your foot muscles and the use of orthotics may help support your leg from below, you may also need to increase support from above, at the hip, by making your buttocks firm and rotating the thigh outward so the knee is centered over the foot. Don't overdo the action by gripping the buttocks onto the tailbone, pushing the pelvis forward, or rolling onto the outer edges of your feet. Use a moderate action, just enough to achieve knee alignment while staying balanced on your feet.
Don't be surprised if you feel soreness in your buttock muscles within a day or two after working carefully on your standing pose alignment. Just be sure to take time to stretch the muscles after you've worked them. Remember, a sore muscle is a worked muscle, and a worked muscle is getting stronger, adding to the stability of your feet, knees, and hips.
Julie Gudmestad is a licensed physical therapist and certified Iyengar Yoga teacher. She runs a private physical therapy practice and yoga studio in Portland, Oregon, where she combines her Western medical knowledge with yoga.