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nfowler50
07-10-1998, 01:25 AM
On the subject of biarticular muscles Sergio wrote :-

>Hello fellows, my name is Sergio and I am a graduating physical
> therapist here in Brazil. I am having a discussion with my comrades
> to which I need help. They say that during the raising phase (geting
> up) of the squat, the simultaneous contaction of the hamstrings and
> gastrocnemius helps to extend the knee (contributing to the
> quadriceps action). I believe that the contraction of those muscles
> actually try to flex the knee (although the knee is extending, of
> course). Their real action is on the pelvis (hamstring) and ankle
> (gastrocnemius).
> So, who is right? Me or them?
> I would be pleased if someone can help. It would be very
> useful
> a reference of some article or text about this problem. Thanks...

The problem of biarticular muscles is particularly interesting.
Initially you need to consider the nature of the linkage between your
ajoining segments. In an open chain the use of the anatomical
classification is true and the muscles in question will act to flex
the knee joint. However, when one of the extremities is fixed or
constrained the anatomical classification loses its validity. So your
question is dependant upon the nature of the linkage between the
segments and the constraints to their movement. Zajak 1993 suggested
that these muscles (HAM, GAS) can act to accelerate the knee in
extension. The SOL was found to be able to accelerate the knee in
extension twice as much as it was to accelerate the ankle joint.

For further details see

ZAJAC (1993) - JOURNAL OF BIOMECHANICS, 26, SUPL 1 109-124

VAN INGEN SCHENAU (1989) HUMAN MOVEMENT SCIENCES 8, 311-337

Neil Fowler + Andre Rodacki

N.Fowler@MMU.AC.UK

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