PP127: Sit-up and Psoas Paradox

[Guest guest]

Here is some discussion from another list about my paradox.

It was written:

<< I agree in principle with your point that straight leg sit-ups are not

automatically " bad " . Your argument that the psoas does not elicit enough

vertical force, is not applicable, however. 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:

*** To which axis of rotation are you referring? The axis passing through

the hip joints or the axes of rotation about certain vertebral joints? There

are several possible axes involved in the execution of the different phases

of the sit-up. In order for anyone to visualise the exact biomechanical free

body diagram, we need to know exactly which axis is being discussed. Even

then, are you suggesting that only one specific axis of rotation is relevant

to the analysis?

Moreover, use of the term " behind " in the context of an axis is not clear to

me so I cannot comment accurately on what you mean. As it stands so far, I

am wondering how magnitude of the perpendicular component (vertical to the

longitudinal axis of the spine) of the force exerted by psoas is influenced

by its being " behind " some the axis passing through the hip joints or some

lower vertebral joints. Please clear this issue of nomenclature up so that I

can respond more intelligently.

Anyway, no matter which nomenclature happens to be used, any reference to the

origins of the psoas in a " normal lordotic position of the supine spine " is

invalid 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 vertebrae 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. >

*** It is impossible for vertebrae to " bulge " forwards, since they are rigid

bones. Even 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

Supertraining/