3.Understanding hip flexors

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Hip flexion plays a vital role in many athletic as well as every day life movements (1). Flexion at the hip involves the action of many different muscles (Figure 1).

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The muscles responsible for hip flexion are:

1. Iliacus
2. Psoas
3. Rectus femoris
4. Sartorius
5. Tensor fascia lata
6. Gluteus minimus
7. Adductor magnus (anterior fibers)
8. Adductor longus
9. Adductor brevis
10. Gracilis
11. Pectineus

In most cases the term “hip flexors” is quite generic or even vague due to the plethora of muscles with different lever arms and therefore different potential for force production at different degrees of hip flexion (2). The study of anatomical leverages of the above muscles has been the central point of our understanding regarding their function during hip flexion. The psoas and the iliacus are the only muscles of the hip flexor group that their insertion is inferior to the pelvis (2, 3). More specifically the psoas has its origin from the length of the lumbar spine, while the iliacus originates on the posterior of the ilium (3). Therefore the psoas and the iliacus are the only muscles with a lever arm above 90º of hip flexion (2, 3). It has been proposed that in the case of a weak psoas or iliacus, the femur may move above the level of the hip, but it is not from the action of these muscles, but rather from the momentum created by the other hip flexors; that is the psoas and the iliacus are the only hip flexors capable of actively bringing the hip above 90º (4, 5).

A simple test to assess the function of the psoas and iliacus is to pull one knee to the chest and release while in a single-leg stance (2). Inability to keep the knee above 90º for 10-15 seconds indicates a weak psoas/illiacus or both (2, 5).

A more advanced test especially for athletic population would be to have your athlete stand with one foot on a plyo box so as the knee is set at above hip height (for most average height athletes this would mean a 60cm plyo box) (4). The athlete places his hands overhead or behind the head and attempt to lift the foot off the box and hold it up for 5 seconds. Inability to lift and hold is indicative of a weak psoas or iliacus, or both (4).

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REFERENCES

1. http://www.mikereinold.com/2011/10/the-importance-of-hip-flexion-strength.html
2. Sahrmann S. Diagnosis and Treatment of Movement Impairment Syndromes. St. Louis, MO: Mosby; 2002.
3. Clark MA, Lucett SC. NASM’s Essentials of Corrective Exercise Training. Lippincott Williams & Wilkins, 2012.
4. Boyle M. Advances in functional training. On Target Publications, 2010.
5. http://www.mikereinold.com/2011/10/functional-assessment-and-exercises-to-enhance-hip-flexion.html