McGill's lab has developed an emg driven computer model which takes into
> account the degrees of freedom of the lumbar spine and most of the
> muscles. The study involved taking emg readings and kinematics from
> normal subjects doing these exercises and inputing the data into the
> model. This gives them a stability index. They then manipulated the
> emg for each muscle. In one trial they would zero the emg for the next
> they would max the emg. They would then get stability indexes for these
> situations. Maxing out or zeroing transversus emg had little effect on
> the stability index. This study of course relies on the validity of
> their model. I think the model is fairly well accepted. I believe that
> Cholewicki and McGill have published studies based on it.
I am always amazed by the ability of peole to develop such complex
modelling - I still have problems geting my VCR to work.
My only comment would be that in a mathematical model where you are able to
maximise and minimise muscles INDEPENDENTLY of each other it may well be
that any one muscle contributes very little to overall stability. The
research of Hodges et al seems to suggest that dysfunction in TrAb is
accompanied by similar dysfunction in MTf, pelvic floor, and diaphragm (jut
that these latter muscles are clinically harder to measure activity levels
in). So that if they modelled, say, a 10% reduction in this GROUP of muscle
combined (ie TrAb, diaphragm, pelvic floor, MTf) it might result in
considerable loss of stability. In vivo I should imagine that this is a more
likely scenario that an isolated reuction in TrAb on its own.
I guess the researchers will have thought of this...
I can see what you mean about Psoas - If you've ever seen an orhopod trying
to dislocate the head of a femur in a hip replacement operstion it's hard to
imagine a need for STABILISING this joint...
----- Original Message -----
From: "Doug Bourne" <[log in to unmask]>
To: <[log in to unmask]>
Sent: Friday, August 23, 2002 1:42 AM
Subject: Re: Movements not Muscles?
> > I think the present model of "Stabilisers" and "Mobilisers" may
> > be dismantled as I suspect muscles are just all somewhere in the
> > but it has proved a useful model during the development and teaching of
> > principle. I think the teaching model is that some muscles are
> > act (from an anatomical point of view) as stabilisers (because they have
> > little leverage to move the joint), and physiologically because they
> > contract with tonic-type contractions, less suited to ballistic
> > However, the contention that stability is due to the concertend effort
> > all muscles doesn't contradict this model - the researchers/teachers I
> > heard lecturing have always insisted that the global mobilisers/local
> > stabilisers are part of a continuum of muscles that work together to
> > and stabilise.
> For the most part Hodges group does a pretty good job with it. The main
> contradiction is that some of the main movers are also the main
> stabilizers. The real problem is when other groups take off on this.
> The kinetic control group is really bad for this. They have divided
> muscles into local stabilizers, global stabilizers, and global
> mobilizers. They are now calling psoas a local stabilizer and are
> promoting exercises like "pulling your hip into the socket." This
> really kills me. Sure the psoas helps stabilize the spine, but it acts
> primarily at the hip. Its not going to act on the spine without it
> acting at the hip. I don't think the hip needs a muscle devoted to
> pulling the head of the femur into the acetabulum.
> > The last point about fear inhibiting TrAb activity I heard about
> > when Paul Hodges presented at the OCPPP meeting here in the UK. They
> > experimented on pigs with a fine-wire EMG and electric shocks (you can
> > when a pig is in fear because it's tail stops being curly - or is that
> > other way round?) and fear = increased delay in TrAb contraction. This
> > very interesting in the context of biopsychosocial models of disability
> > where disability is intimately related to fear-avoidance behaviour and
> > health beliefs.
> It looks like they have moved on to zapping humans.
> Another link to biopsychosocial models is that Marras has shown that
> there is an increase in spinal loading when subjects are put under
> Jason: The conference was mostly research based so no one presented any
> practical info. I think that McGill still promotes those exercises as
> part of a stability program.