Here is some further discussion from another list on my paradox :
It was written:
<< I agree in principle with your point that straight leg sit-ups are not
automatically "bad"... It is not necessary for the psoas to elicit direct
vertical force - the origins of the psoas in a normal lordotic position of
the supine spine, are behind the axis of flexion/extension. >
Mel Siff:
*** Any reference to the origins of the psoas in a "normal lordotic position
of the supine spine" is redundant because the curvature of the lumbar spine
immediately flattens in the healthy spine during the initial phase of the
sitting up action from the supine position when the head and shoulders are
raised. I have yet to come across any member of the general public who
begins the sitting up action with unrestrained feet without first raising the
head and shoulders. Only after this initial curling up or lumbar flexing
stage is completed does any action of the psoas become significant, but, by
this stage the lumbar spine is already in pronounced flexion and it is
impossible for any level of psoas activation to cause lumbar extension, let
alone hyperextension.
In my original paradox, I suggested that anyone who doubts that it is
impossible or virtually impossible for psoas to play a significant role in
the early stages of sitting up to try to begin the sit-up (with unrestrained
feet) with head and shoulders touching the floor and forcing these parts of
the body to leave the floor LAST, not first during the exercise - i.e. by
eliminating all trunk flexion caused by early abdominal action and allowing
the hip flexors to raise the trunk from the floor from start to finish of the
movement. Did you actually try this unkind practical exercise before
commenting on this paradox? You might find it very revealing and very
humbling.
<When the psoas contracts parallel to the spine (without abdominal
antagonism!) the spine will "bulge" forward into more lordosis..... Is this
dangerous? If done repeatedly in this manner (for many many reps), I could
see a potential for problems, but straight leg sit-ups are not dangerous for
the spine when performed properly - and that needs good coordination with the
abdominals. >
*** If you are referring to some vertebrae being compelled by shearing force
to exhibit anterior gliding or dislocation, the possibility of this occurring
to any noticeable degree in the healthy spine is minimal because the
vertebrae are held very firmly in position by many extremely strong
connective tissues which will resist any attempts at any local displacement
of one vertebrae relative to its neighbours. Then, as I pointed out earlier,
the lumbar spine has already moved into a position of very pronounced flexion
by the time psoas is called upon to contribute to the execution of the
sit-up, at which stage even extremely large levels of psoas tension will
never be able to force the lumbar spine into hyperextension.
In short, all of the theorising about psoas dangers, even if the person has
poorly developed sitting up skills, is vastly exaggerated because the
structure of the body and the biomechanics involved make it impossible for
anyone to produce high levels of psoas tension during the early stages of
sitting up when the lumbar spine is most susceptible to the effects of
anterior shear. Because the average person is far too weak to ever initiate
a sit-up by significant action of psoas and because nobody ever tries to sit
up from the supine position without first raising head and shoulders, it
appears to be a persistent myth that the hip flexors will ever be activated
to such a degree during any stage of the slowly executed sit-up (with
unrestrained feet) to cause lumbar trauma.
Dr Mel C Siff
Denver, USA
http://groups.yahoo.com/group/Supertraining/
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