What Is the Definition of Flexion Bias?

Bending over
Bending over. Andy Reynolds/Collection:The Image Bank/Getty Images

Flexion Bias

With some back conditions, specific positions are known to help manage symptoms. These positions are known as biases. There are three types of biases: flexion, extension and non-weight bearing. Taken together, these biases are called direction preferences.

If your back feels better and/or your symptoms abate when you bend forward, it's likely that the injury or condition you experience has a flexion bias.

For example, spinal stenosis, which is a condition that narrows the space in the intervertebral foramen, generally has a flexion bias.  Many people with spinal stenosis find that bending their spine forward (aka spinal flexion) make it feel better.  The reason is that bending forward makes more space in the intervertebral foramen.  This, in turn, allows the nerve that passes through the foramin to do so without being touched or pressured by nearby (and quite often misshapen - due to arthritis) bone.

Other conditions that usually have a flexion bias include spondylosis and spondylolisthesis.

For injuries and condition with a flexion bias, symptoms tend to increase when your back is extended (arched).  

Extension Bias

The opposite of flexion bias is extension bias.  As you can probably guess, an extension bias occurs when the movement of arching your back makes your symptoms feel better.  Examples of conditions that tend to have extension biases are herniated and bulging disc.

 People who have either of these conditions often find that when they bend forward (into spinal flexion) their symptoms worsen, and as already stated, when they arch their back, it feels better.

Directional Preferences Help Classify Your Low Back Pain

Flexion bias (along with extension bias and non-weight bearing) are part of a non-patho-anatomical system of classification for mechanical low back pain, specifically disc problems, facet joint pain or dysfunction, sacroiliac joint dysfunction and spinal instability due to a problem in the pars (which is an area at the back of a vertebra where processes emanate.

 These processes become part of the facet joints.)

I realize that "non-patho-anatomical" is a bit of a mouthful so let's unpack the term.  

Rather than what your MRI or X-ray reveals about your spine, the non-patho-anatomical system takes its cue (for evaluation and treatment choices) from the symptoms you report and what your therapist observes in your movements.

This system is used in the McKenzie and other physical therapy treatment methods. 

The patho-anatomical approach to classifying low back pain is widely in use, and likely more so at the doctors office, rather than the physical therapy clinic.  This may leave some physical therapists in a bind, as their way of working involves more face to face interaction with the patient.  

About this, Nachemson, in his article, "Scientific diagnosis or unproved label for back pain patients. Lumbar Segmental Instability," says the following:

The patho-anatomical method of diagnosing mechanical low back pain may be beneficial to Physicians and Surgeons, but how do these medically adopted methods of diagnosis help physical therapists in their management of MLBP? Can physical therapists actually change any patho-anatomical conditions by their non-invasive treatment techniques? Can herniated discs be reduced, or can degenerative changes in zygapophyseal joints and intervertebral discs anatomically change following conservative methods of treatments?

In fact, an overemphasis on the simplistic biomedical approach of identifying and treating the structural cause of pain has led to excesses in diagnostic testing, bed rest, narcotic analgesics, and surgery.(Waddell 1998).


Kinser, C., Colby, L.A., Therapeutic Exercise: Foundations and Techniques. 4th Edition. F.A. Davis Company. Philadelphia, PA. 2002.

Dunsford, A., Kumar, S., Clarke, S. Integrating evidence into practice: use of McKenzie-based treatment for mechanical low back pain. J Multidiscip Healthc. 2011.

Nachemson, A. Scientific diagnosis or unproved label for back pain patients. Lumbar Segmental Instability. Szpalski M, Gunzburg R, Pope MH eds. Philadelphia: Lippincott William & Wilkins, 297-301.http://www.aptei.com/articles/pdf/IRSAT_1.pdf

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