In this postural alignment the neck is slightly extended, the upper back is in slight flexion, and the lower back is in slight extension.1 The slightly extended inward curve of the neck (cervical spine) and lower back (lumbar spine) is referred to as lordotic. In this way a normal slightly arched position of the neck and lumbar in a position of lordosis. However, this term is generally meant to mean a hyper-extended or over-arched position.
|Cervical Spine||Normal Curve, Slightly Convex Anteriorly|
|Thoracic Spine||Normal Curve, Slightly Convex Posteriorly|
|Lumbar Spine||Normal Curve, Slightly Convex Anteriorly|
When the lower back is normally curved the pelvis is in a neutral position. Notice, in the image to the right that the two most prominent parts at the front of the pelvis, the anterior-superior iliac spines(ASIS) and the symphysis pubis (PSIS) (figure 2, number 8), are aligned vertically. According to Kendall, this indicates an ideal alignment of the pelvis 1 and clinically, an angular deviation between the ASIS and PSIS of less than 5 degrees is concidered normal. However, variations as much as twelve degrees have been found in cadaver studies and so a perfectly vertical alignment should not always be expected. 2
The normal upper back or thoracic region (below the neck) is in a slightly flexed or "rounded" position.
In this alignment the abdominal and hip extensors and the lumbar and hip flexor muscles are in perfect opposition to one another. The former group tilting the pelvis posteriorly (to the back) and the latter tilting it anteriorly (to the the front) resulting in a neutral pelvic position.
Pelvic Inclination, Lumbar Lordosis, and Muscle Length
The information above is based on the widely accepted relationships presented by Kendall, et al. 1. However, the reliability of these relationships are currently in question and our understanding of the influence of pelvic inclination on lumbar lordosis is in flux.
It is generally accepted that the pelvic rotators, the abdominals and the erector spinae influence the lumbar curve and pelvic inclination in a standing position. The abdominal muscles tilt the pelvis posteriorly. When the pelvis is tilted to the rear, the degree of lumbar lordosis decreases. The erector spinae tilt the pelvis anteriorly. When the pelvis is tilted toward the front, the degree of lumbar lordosis increases. Therefore, it seems logical to assume also that the length of these sagital-plane pelvic rotators will influence the pelvic inclination and thus the degree of lumbar curvature.
Recent studies, however, have questioned these assumptions. To date, standing postural alignment has been used to make predictions about the performance and length of the abdominal and erector spinae muscles. This practice may be erroneous, as some studies have indicated that there is no relationship between these variables and that posture must be controlled by several complex factors.
Furthermore, Kendall and colleagues postulate a relationship between lumbar lordorsis, anterior pelvic tilt, and hip flexor (and low back) shortness. As well, there is a supposed relationship between hamstring tightness and posterior pelvic tilt. All these relationships give rise to various postural distortions. These relationships have been further used to assign muscle stretching techniques as a means to correct postural deviations.
As things stand all these assumptions may be seriously questioned. Ongoing studies are failing to support the relationships proposed by Kendall, et al. and the wisdom of predicting muscle length and performance from standing posture should be considered unproven. 3,4
1 iLiac crest 2 Ilium 3 Ala 4 Sacral promontory 5 SacroiLiac joint
6 Acetabelum 7 Obturator Foramen 8 Pubic symphysis 9 Pubic arch
10 Pelvic Brim
This page created 15 Dec 2009 20:44
Last updated 08 Feb 2013 18:55