PP127: Sit-up and Psoas Paradox

[Guest guest]

Here is a response from someone on another list to my PP127. Any comments on

these comments?

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* Some comments on PP127:

1) Straight-legged sit-ups are safer than bent-knee sit-ups.

In straight-legged sit-ups, the psoas is allowed to function more efficiently

along with the other spinal flexors. In supine (supposing the individual is

in a good posture with no excessive anterior or posterior pelvic tilt) the

psoas and abdominal muscles are positioned at an adequate length from origin

to insertion. With a contraction the abdominals (spinal flexors) flex up the

trunk by pulling strongly against a fully anchored pelvis. The Sit-up part of

the action occurs after the trunk has been raised -- this is where the psoas

comes into play. The psoas flexes at the hip (it is a hip flexor) to complete

the trunk curl/sit-up maneuver.

2) Sit-ups are not always the safest, depending on your postural tendencies.

If you are predisposed to a posteriorly rotated pelvis (relatively shortened

hamstrings and rectus abdominis) or anteriorly rotated pelvis (relatively

shorted psoas and lengthened abominals) sit-ups with only increase the

tendency for malalignment. Only when one is able to achieve a centered

(neutral) pelvis/spine position should the sit-up be executed.

Those with shortened psoas muscles would do better to start out with the

knees bent (putting the psoas on slack) with the goal of supplementing thia

exercise with postural education and stretching of the psoas. Those with

shortened hamstrings can start out with straight legged sit-ups but may

benefit from a towel roll under the low back to encourage a more proper

alignment. Also these individuals should receive heavy postural education and

stretching of the hamstrings (and often the ERs of the hip). In addition,

both individuals should begin with strengthening the core musculature

(multifidi, pelvic floor, transverse abs) to be able to achieve neutral pelvis

/spine and to develop adequate control of this position.

Mel Siff:

<Theoretically it might appear to some folk that the small angle subtended in

the straight-legged sit-up by psoas in its proximal attachment to the spine

will markedly accentuate the lumbar concavity (as seen from behind), this

does not appear to have been shown via clinical measurement. If the psoas

angle were more perpendicular to the length of the spine, then it would be

far more likely for the psoas to exert sufficient force to increase the

lumbar concavity, but the major component of force exerted by psoas is along

the length of spine, not vertical to the spine.>

* Only during the trunk curl is the psoas force 'along the length of the

spine.'

Mel Siff:

<Paradoxically, the bent-knee (actually flexed-hip) sit-up would seem to

place psoas in a position which enables it to pull more vertically on the

lumbar spine, so that that flexed hip sit-ups would appear to be less safe

than straight-legged sit-ups! As a matter of interest, has anyone come

across any MRIs which have examined exactly how much an activated psoas in

a healthy person during sit-ups increases the lumbar concavity (not

'lordosis', since this term accurately refers only to pathology)? Actually,

lordosis is the natural alignment of the cervical and lumbar spine areas.

When this lordosis is accentuated, it becomes pathological.

All too often, it is presumed that large psoas activation necessarily can and

will produce enough force to deform the lumbar spine to such an extent that

it will lead to vertebral displacements which will cause nerve impingement in

the non-pathological spine. Surely, the likelihood that this level of

displacement will occur is vastly exaggerated because the healthy spine and

its discs are surrounded by very strong connective tissue that minimise the

degree of this displacement.>

* Most individuals with altered pelvic positions have been positioned as such

for their entire lifetimes. This is sufficient time for their body to develop

an area of local defamation such that a repetitive strain by the psoas

(increased anterior tilt/Lumbar lordosis during a sit-up) will cause a small

amount or vertebral displacement. Also, those with posterior pelvic tilts can

develop higher risk of disc bulge if engaging in activities where the spine

is flexed repetitively and to the point of ligamentous failure (we all have

patients like this).

Mel Siff:

<What is far too commonly assumed is that psoas definitely DOES increase the

lumbar concavity, and in order to do so, it has to produce extremely large

force because of its low angle in the supine or straight body.>

* Remember, most individuals with a life-long positioning of accentuated

lumbar lordosis have psoas muscles in a relatively shortened position. Their

mechanical ratios are unbalanced.

Mel Siff:

<Moreover, it is impossible or virtually impossible for the average person to

sit up in such a way as to allow psoas to strongly become activated before

the rest of the abdominal musculature has become activated and minimised the

possibility of this happening. >

* You're right. The trunk curl part is primarily a result of the abdominals

activating. The sit-up (hip flexion part) is the area of concern. BUT, as

with a forward bend in standing, most anteriorly positioned individuals with

never assume a neutral lumbar spine -- their psoas is tight and will activate

prematurely.

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Dr Mel C Siff

Denver, USA

Supertraining/