> I think, on its own, it may well be that TrAb plays a minor part in
> stabilisation - I know it has to work in concert with the diagphragm and
> pelvic floor muscles to be effective but I would like to hear more about the
> research showing "that transversus abdominus is only a very minor
> contributor to spinal stability during a selection of spinal stability
> exercises". Do you know more about this - how do you research an individual
> muscles degree of contribution to stability?
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 think the present model of "Stabilisers" and "Mobilisers" may eventually
> be dismantled as I suspect muscles are just all somewhere in the spectrum
> but it has proved a useful model during the development and teaching of this
> principle. I think the teaching model is that some muscles are positioned to
> 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 movement.
> However, the contention that stability is due to the concertend effort of
> all muscles doesn't contradict this model - the researchers/teachers I have
> heard lecturing have always insisted that the global mobilisers/local
> stabilisers are part of a continuum of muscles that work together to move
> 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 recently
> 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 tell
> when a pig is in fear because it's tail stops being curly - or is that the
> other way round?) and fear = increased delay in TrAb contraction. This is
> 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.