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Anatomy in Action: The Psoas Major

The psoas major is one of the most controversial muscles among Pilates teachers and anatomy nerds. It’s a critical muscle for functional movement of any kind and affects almost everything we do, from sitting and standing to running and dancing. It connects the spine, pelvis and femur and is the primary muscle on the front of the lumbar spine (Gilroy et al. 2012). It plays a central role in hip flexion and supports the low back’s position to create good (or not so good) posture. If you’ve ever done a teaser in Pilates, a boat pose in yoga or a full sit-up at the gym, you’ve felt the action of the psoas major.

The psoas major is commonly blamed for low-back and hip pain. When it’s out of balance with the abdominals, back muscles and hamstrings, and with the rest of the hip flexors, it’s prone to shortening and pulls the front of the lumbar spine into lordosis (Page, Frank & Lardner 2009). This can put pressure on the low back and lead to discomfort, pain or injury. Many people’s daily routines—driving to work, sitting all day, driving home and then sitting to watch television—contribute to a short, stiff psoas major. Help clients to counteract this by regularly working the psoas major in a full range of motion to keep the muscle supple.

The Anatomy of the Psoas Major

The psoas major is like a river with many “streams” running into it. These streams connect the vertebral bodies, intervertebral disks and transverse processes of the 12th thoracic vertebra (T12) through the 5th lumbar vertebra (Gilroy et al. 2012). Each vertebra contributes more muscle fibers to the river until the psoas major becomes a relatively thick band of muscle that creates two columns of support along the front of the spine. This muscle band also balances the big columns of the erector spinae along the back of the spine (Gilroy et al. 2012). The psoas major crosses the pelvis and merges with the iliacus to form a common tendon that attaches to the lesser trochanter on the upper inner femur bone. Because these muscles share a common attachment, they are often referred to jointly as the iliopsoas. Both muscles have the same action at the hip, but the psoas major connections on the spine create distinctly different actions in the torso.

The Many Actions of the Psoas Major

The psoas major has different actions, depending on the body’s position. If the pelvis and torso are stable, as when a person is lying on the floor, the psoas major is a powerful hip flexor for abdominal exercises involving the lower body (e.g., double straight-leg stretch). Since this muscle is the primary hip flexor above 90 degrees, this is a useful range to strengthen it in (Clippinger 2006). When moving the legs away from the torso, it’s important to use the abdominals to stabilize the lumbar spine so the psoas does not pull it forward as the legs lower. Otherwise, pain may result. In Pilates, where many moves include lowering the legs away from the torso in a supine position, it’s important to place extra emphasis on keeping the low back stable as the legs lower. This is critical for low-back safety and is a primary training principle for the psoas major and other hip flexors.

Because the psoas major attaches to the front of the spine, it is important to strengthen it in a balanced and progressive manner. Clients with low-back, pelvic or hip pain may have major weaknesses or imbalances, and an aggressive strengthening program may exacerbate symptoms.

Key Exercises for Strengthening the Psoas Major

Level 1: Supine hip flexion. Lie supine with feet on the floor, and lift one leg at a time into hip flexion by bringing the thigh toward the chest. Allow gravity to assist in lifting the leg above 90 degrees. To check low-back stability, place your hands under the client’s waist and maintain back position as the legs move. Lumbopelvic stability is critical for successfully training the psoas. Begin with no more than 10 repetitions; alternate sides.

Level 2: Seated hip flexion. Sit on a chair or bench for the basic exercise or on a stability ball for an additional challenge. Lift one leg at a time into hip flexion (above 90 degrees) while keeping the abdominals engaged and the low back stable. Place your hands on the client’s low back to make sure it is not moving as the leg lifts. Gravity resists the lift and increases the challenge. Gradually build up to 10 repetitions; alternate sides.

Level 3: Standing hip flexion. Stand with one hand on a barre or the wall for support, and lift one leg into flexion above 90 degrees, knee flexed. Keep the hips level and the low back stable as the leg lifts. As the hips get stronger, move the leg from a neutral, parallel position into lateral rotation and abduction to challenge the psoas major in different angles and to create more dynamic, multiplanar suppleness and strength. If the client has the flexibility, she can extend the leg to increase the lever length. You may also increase the challenge or resistance by adding light ankle weights, cables from a low angle or springs around the thighs when using a Pilates springboard, tower or trapeze table.

When strengthening the psoas major, work on balancing both sides of the muscle. Identify any imbalances early in the training process, and correct them by performing additional repetitions or sets on the weaker side. Note: When working with an injured client, be sure to progress gradually in order not to cause a flare-up.

Dynamic Strength, Flexibility and Suppleness

If you want to create dynamic strength, it’s important to train for flexibility and suppleness. There is ongoing controversy among kinesiologists and fitness experts about the benefits of stretching the psoas major, but most seem to agree that in order to maintain the right amount of flexibility, the muscle must be worked dynamically through its full range. For many clients, actively working the psoas at the end ranges of motion can help to increase hip and low-back mobility and comfort, counteracting the effects of sitting. Lunges are a good choice because the muscle engages eccentrically in order to hold the stretch rather than being passively stretched.

To help clients develop range of motion and suppleness in the psoas major, try these exercises:

  • Stand or kneel in a lunge position and straighten the back leg as much as possible without tilting the pelvis anteriorly.
  • Gently pulse down and up in the lunge or add a slight pelvic posterior tilt to enhance the stretch and to work dynamically.
  • Pulse or posteriorly tilt 10 times before changing sides.
    Have clients perform these stretches at least three times per week to maintain range of motion and flexibility. If you’re working with a client who has limitations, have him do the stretches daily. With the psoas major, it’s especially important to combine flexibility and strength training to optimize the muscle’s full functional range.

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