While discussing the role of Psoas,I would suggest visiting
www.kineticcontrol.com,and click on "publications".
There's a paper specifically on Psoas by S Gibbons.He argues that the muscle
has a stabilising role,and does not contribute significantly to the actual
movement of hip flexion,if I recall correctly. Any feedback would be
interesting-there's some other stuff there which might raise a few eyebrows!

                                      Nigel Biggs
                                      hysiotherapist,UK


-----riginal Message-----
From: [log in to unmask] <[log in to unmask]>
To: [log in to unmask] <[log in to unmask]>
Date: 24 April 2002 11:02
Subject: PP127: Sit-up Paradox and Siff


>[log in to unmask] writes:
>
><< I wondered if Mel McSiff is still a member of this mailserver. I kinda
>miss his input ;o). >>
>
>*** By the way, even though my gradparents on one side were Scots, my name
is
>not McSiff.   My Scots middle name is Cunningham, from bonnie Burns
country,
>but my last name is Siff, from way across the Baltic Sea!
>
>[log in to unmask] writes:
>
><< I don't know if Mel Siff is still a member but my understanding is he is
>currently doing some seminars in Sweden and isn't easily contactable at the
>moment.  So maybe we will hear from him when he returns home (if he is a
>member). >>
>
>***Thank you for the interest, my friends!  Indeed, I have been lecturing
at
>conferences in Sweden and have just returned from some time in those lovely
>Scandinavian climes.  I not only am pleased to return to the fray, but wish
>to share another Puzzle & Paradox (PP127) in my ongoing series.
>
>INTRODUCTORY NOTE
>
>For newcomers to this forum, these P&Ps are Propositions, not facts or
>dogmatic proclamations. They are intended to stimulate interaction among
>users working in different fields, to re-examine traditional concepts,
foster
>distance education, question our beliefs and suggest new lines of research
or
>approaches to training.  We look forward to responses from anyone who has
>views or relevant information  on the topics.
>
>PP127  The risks of straight-legged sit-ups may be grossly exaggerated in
the
>healthy individual, especially regarding the action of the hip flexors on
the
>lumbar spine.
>
>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.
>
>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)?
>
>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.  This
>certainly is correct IF one assumes that psoas always definitely increases
>the lumbar concavity.  This assumption seems to be totally incorrect,
because
>the poor mechanical advantage of psoas in the supine position does not
permit
>it to produce high levels of torque about the hips.  One probably could
>insert microelectrodes directly into psoas to electrically activate it in a
>supine person and we still would not be able to generate sufficient
vertical
>force to produce enough torque to deform the lumbar spine, at least to an
>extent which causes spinal pathology.
>
>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.
>
>Then, even if the lumbar spine is subjected to large psoas forces, adjacent
>vertebrae are not going to experience local dislocations which will produce
>nerve impingement - instead the lumbar spine, according to basic mechanics,
>is simply going to exhibit a slightly smaller radius of curvature over a
>length of many vertebrae.  It certainly will not experience the type of
>deformation and discal stress that is imposed when the lumbar spine is
>subjected to loaded flexion and rotation.
>
>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. The very act of raising the head and
shoulders
>during the early stages of sitting up activates the abdominal musculature
so
>strongly and increases the psoas angle to such an extent that the ability
of
>psoas to increase the lumbar concavity is minimal.  If this point is
doubted,
>try sitting up by keeping the back of your head and shoulders in touch with
>the floor while starting a sit-up and attempt to raise your trunk by
relying
>largely on psoas action.  First of all, this will not be possible unless
your
>feet are restrained and you are extremely strong, which hardly is the case
>with the average fitness fan.
>
>Does all of this not suggest that most or all of the well-meaning advice
>about executing sit-ups or crunches is exaggerated or redundant, especially
>regarding the risks of psoas activation necessarily imposing pathological
>levels of stress on the lumbar spine or its components?  Does the body not
>automatically act to minimise the risks of any high levels of stress as
soon
>as the head and shoulders are raised during the early stages of any supine
>sit-ups or 'crunches'?  Comments from anyone?
>
>Dr Mel C Siff
>Denver, USA
>http://groups.yahoo.com/group/Supertraining/
>