Can you explain what muscles are shortened and what muscles are then lengthened when a patient is in a posterior pelvic tilt and an anterior pelvic tilt?

Lordosis is a state of exaggerated curvature of the lumbar spine with excessive anterior pelvic tilt i.e. there is an exaggerated lumbo-pelvic angle that is more than 60° in women and 55° in men. In this condition, the body weight is transferred from the strong, broad, supportive portion of the vertebral bodies to the more delicate arches. In addition, there is a protruding concavity of the lumbar vertebrae, a protruding and slack belly as well as a protruding buttocks.

The abdominal muscle group plays an important role in the presentation of a pelvic tilt. Weakness (read lengthening) of the abdominal muscles may cause excessive anterior tilt and subsequently, in a chain reaction, affect stability of the lower back eventually increasing lumbar lordosis.

In an anterior pelvic tilt, shortening (read tightening) of the hip flexors (chiefly the iliopsoas) tends to pull the lumbar vertebrae forward. In addition, the rectus femoris, quadratus lumborum and the sartorius muscles are all shortened as well. In summary, weakening of the hip extensors with a concomitant shortening of the hip flexors will result in an anterior pelvic tilt.

In a posterior pelvic tilt (AKA ‘flat back’), in addition to the weakening of the abdominal muscles as well as the inhibition (weakening) of the hip flexors and lumbar spine extensors, the gluteus maximus and hamstring muscles (i.e. semitendinosus, semimembranosus and biceps femoris) are all tightened as well.

Posterior pelvic tilt is not as common as anterior pelvic tilt. The dominance of sedentary positions in our daily lives tend to place stress on the pelvis causing anterior pelvic stress. However, posterior pelvic tilt still causes lower back pain for many people.

Depending on the particular tilt presentation, interventions are directed towards strengthening and shortening weak or lengthened muscles while lengthening shortened muscles in a bid to make them more flexible.

Ref 1.

Ref 2. Solberg G. Postural Disorders and Musculoskeletal Dysfunction: Diagnosis, Prevention and Treatment. 2008. Second edition. Churchill Livingstone Elsevier Publishers. Part 2. Survey of common postural disorders. Chapter 3. Postural disorders of the spine: sagittal plane. Lordosis. Pgs. 82-83.