Flat Back Posture

In the "flat back"1 postural alignment, the cervical spine is slightly extended, the upper thoracic spine is in flexion, the lower thoracic straight, the lumber straight (flexed) and the pelvis is posteriorly tilted. 1 See Muscles: Testing and Function, with Posture and Pain by Kendall, et al.

The normal lumber spine (lower back) has a slightly extended inward curve, called lordosis. In individuals with the flat back posture, the pelvis is tilted toward the rear and the lumber has lost this lordosis, causing it to be flat, which is actually a flexed position for this portion of the spine. People with flat back will tend to stand with their hip and knees hyper-extended and their head forward.

This deviation from ideal spinal alignment is marked by and sometimes called posterior pelvic tilt. This describes the backwards rotation of a the superior iliac spine (ASIS) in relation to the pubes of the pelvis. Laypeople can just think of this at the "top" of the pelvis tilting toward the rear.

Individuals who display this posture, besides having the appearance of a very flat back, will also show the appearance of a flat buttocks that is tucked under.

According to Kendall, et al. and commonly accepted, the one-joint hip flexors (iliopsoas) will tend to be long and weak; the hamstrings short and strong. The erector spinae will be elongated due to the loss of anterior curve but they will not necessarily be weak. The abdominal muscles may be strong. There has been little evaluation of these proposed relationships between muscle length and postural alignment and little agreement exists in the most current literature. 1

Head Forward
Cervical Spine Slightly extended
Thoracic Spine Increased flexion
Lumbar Spine Flexed (straight)
Pelvis Posterior Tilt (tilted backwards)
Knees Hyperextended
flat back posture

Flat Back Posture

One study found that, although hamstring stretching is commonly advised to correct the pelvic tilt and so the flattened lumbar position, there was no difference in the lumbar position and pelvic tilt of a hamstring stretching and control group, indicating no support for the relationship between hamstring length and flat back posture. Furthermore, according to the authors, another study found that hamstring length was negatively related to lumber curve. Hamstring stretching was found, however, to increase forward bending ROM. The author's incorrect method for using the straight leg raise test to assess hamstring length was called into question by one commenter and there are still many questions as to the actual relationship between hamstring length and flat back posture. 2

Conscious alterations in posture, mobility, and stability exercises are more likely to correct postural deviations and/or prevent future injury than stretching singles muscles. The flat back, of all the postural deviations, is considered the most likely to result in lower back injury. Decreased curvature of the spine is thought to increase risk by decreasing the normal shock absorbancy of the spine.

Flat Back Confusion

Flat back, as stated, refers to a postural deviation in which the lumbar has lost its normal curvature (lordosis). It is associated with a kyphotic position of the thoracic spine and a head forward position of the cervical spine. Flat should not be confused with neutral. A neutral position of the lumbar spine is one in which the spine retains its normal slight extension.

Strength trainees are often instructed to lift with a "flat back" when the instruction actually refers to a neutral back. This is when the pelvis is in a balanced "neutral" position without excessive posterior or anterior tilt, which entails a normal lordosis of the lumbar. See Ideal Postural Alignment (Normal Posture)

Keep in mind that dynamic functional activities and exercises move through the neutral position of the spine. Any rehabilitative program involving correction of excessive lumbar flexion (posterior pelvic tilt) should eventually progress to pain-free movement through the neutral position and beyond.

References
1. Kendall, Florence P., et al. Muscles testing and function with posture and pain. Baltimore, MD: Lippincott Williams & Wilkins, 2005.
2. Li, Yenche, Philip W. McClure, and Neal Pratt. "The Effect of Hamstring Muscle Stretching on Standing Posture and on Lumbar and Hip Motions During Forward Bending." Physical Therapy 76 (1996).


This page created 25 Sep 2011 19:08
Last updated 20 Sep 2013 14:16

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