Dear List Members,

We´d like to know what the relationship with upper gluteus maximus/iliotibial band system and initial contact. How does this action occur to extend knee?
Cited by Jacquelin Perry's book.

Best regards

Paula Horta Andrade PT scholarship
AACD Gait Lab - Sao Paulo - Brazil

Can't let that one go.

Really, I think the answer is that nobody knows (this harks back to the recent teach-in on
Lombard's paradox) - you have to run it through a model to know for sure.

But... it seems to me that there are two possibilities (feel free to suggest more, everyone!):

At the hip:

1. Push-from-behind power, which Winter claimed was the second largest contribution to forward progression after ankle push-off.
2. Prevention of jack-knifing (sudden forward flexion of the trunk when the hip comes to an abrupt stop) on initial-contact. This is what Winter eventually concluded. The acceleration at the hip is attenuated by the time it reaches the head and he thought this was the main mechanism. I have to say that I have never fully accepted this idea because the hip power at initial contact is positive (concentric) this surely agrees more with #1. We'd expect it to be negative (eccentric) if Winter's hypothesis were correct.

For the same reason, your suggestion that "Gluteus Maximus (together with the hamstrings) stops the flexion of the hip " doesn't seem plausible, because hip power is positive at this time.

I suspect you've opened yet another can of worms...

Chris

Dr. Chris Kirtley MD PhD
Associate Professor
Dept. of Biomedical Engineering
Catholic University of America
620 Michigan Ave NE, Washington, DC 20064
Tel. 202-319-6247,  fax 202-319-4287 

Yes, the answer is probably more complicated than my textbook driven answer (in this context I consider the ESMAC course notes as a textbook).

Your first suggestion relates to events after initial contact.

You reject suggestion 2 based on the fact that hip power is positive as
opposed to negative. Two points related to this. After initial contact the
force platform's accuracy is low due to the small forces. The calculated hip
power is only slightly positive after IC and I wonder if the error of the
force measurement contaminates this finding. The other point is that the hip
power on a conventinal gait printout is the sum of all powers acting around
the hip in 3D. Anything we read off the curve cannot be directly linked to
the sagittal plane only.
For example at the ankle joint there is power generation after initial
contact when we would expect absorption during the first rocker. This
conflict can be resolved if we move on from the sagittal into the frontal
plane.

Now I'll try to put together hip and knee angles and moments before initial
contact.

The hip is flexing and the knee is extending. The joint activities of the
Gluteus maximus and the Hamstrings brake knee extension and hip flexion.
(The stunning video of the mechanical model from CELOS shows that the
hamstrings in fact flex the hip, but the Gluteus maximus was not part of the
model. It would be interesting to see what happens to the model if the
Gluteus maximus is included. We typically consider only a subset of all the
muscles involved and this may lead to confusion.)

Chris, you question whether the Hamstrings and Gluteus maximus stop the
flexion of the hip because the power at that time is positive when it should
show absorption (braking). This can be resolved by separating midswing and
terminal swing. In midswing the hip flexes with simultaneous activity of the
Hamstrings and Gluteus maximus (and so we expect power absorption), in
terminal swing it extends (minimally). The measured positive power occurs in
terminal swing when the hip extends.

The question is why we can not measure the hip power absorption in mid
swing? Because it is not coming from the hip. We talk about the extension of
the knee but in fact that is a consequence of the whole shank rotating
forward. The forward movement (rotation) of the mass of the shank may
generate enough moment around the knee axis to force the thigh in a way
which brakes hip flexion. So the hip stops flexing but we don't see power
absorption in the hip joint because it originates from the shank.

Gabor

--
Dr Gabor Barton (MD)
Senior Lecturer in Biomechanics
The Research Institute for Sport & Exercise Sciences,
Liverpool John Moores University
Room 2.51 Henry Cotton Campus, 15-21 Webster Street, Liverpool, L3 2ET
Tel: +44 (0)151 231 4333/4321   Fax: +44 (0)151 231 4353

As I predicted, this is a can of worms! I'm annoyed now that I didn't think of it for a Teach-in. We have discussed heel-strike forces once before, though: /teach-in/transient

OK, let's try to bring some facts to bear on the situation. I think you quite rightly raise the issue of validity of inverse dynamics at the hip, in view of the low forces (and therefore dubious center of pressure) but there is also the problem of error propagation from distal joints and errors in inertial forces (particularly in terminal swing) from imprecise anthropometry.

But I think we can lay these worries to rest, thanks to Georg Bergmann's great work in Berlin with force transducers implanted within hip arthroplasties. He has found a good match between his directly measured forces and those calculated by inverse dyanmics - see, e.g.:

Heller, Bergmann et al, Musculo-skeletal loading conditions at the hip during walking and stair climbing. Journal of Biomechanics 34(7) (July 2001): 883-893. The full paper is available here via the (still free!) JoB site (sorry for the ludicrously long link):

http://www.jbiomech.com/library.exe?action=articles&source=now&node=TOC@@BM@34@7&site=BM&m1=5&m2=1&jcode=BM

Note that this issue has several papers addressing this question. I do think these studies provide overwhelming evidence that inverse dynamics is valid at the hip.

Your other point suggested that it is the lumping of frontal (and transverse) power in with sagittal plane value. I confess I'm a bit sceptical, since Winter's work was only 2D anyway. But please fight your corner if you still think this is relevant.

I do take your point about the hip angular velocity being minimal at initial contact, though, and to be honest, hip power is usually not very large at contact, but comes up after about 10% cycle - see my figure, drawn with Andreas' data: /data/kinetics.jpg - power is really zero at this time.

I do think it is time we talked about what H1 power is for, though. I suspect this is separate issue, because it occurs, as I say, a little later. I'd like to know if anyone out there (Steve Piazza, Rick Neptune, Pat Riley and Tom Keppel come to mind!) has any power flow of induced acceleration data that might shed light on this?

Dr. Chris Kirtley MD PhD
Associate Professor
Dept. of Biomedical Engineering
Catholic University of America
620 Michigan Ave NE, Washington, DC 20064
Tel. 202-319-6247,  fax 202-319-4287 

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