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unknown user
07-22-1999, 02:06 AM
The question was:

Does someone have a guess what would be the implications on the role of uni
and biarticular muscles, i.e., the biarticular muscle will still be able to
uniquely control the direction of the external vector (Jacobs & Van Ingen
Schenau, 1992: Doorenbosch & Van Ingen Schenau, 1995)? And the uniarticular
muscles will still be able to produce most propulsive force/work, without
having any influence over the movement control (Doorenbosch et al., 1997)?

Is someone interested in discussing (speculating) these issues?

André Rodacki

Manchester Metropolitan University
Department of Exercise and Sport Science
Hassal Road, Alsager, UK
ST7 2HL


_______
Warren Darling replied:

Actually, some biarticular muscles may be isometric throughout much of the
jump. During the counter-movement, the hips and knees flex so the hamstrings
and rectus femoris do not change length much and the ankles dorsiflex so the
gastrocnemius does not change length much (i.e., knee flexion/ankle
dorsiflexion). Similarly, during the extension phase the motions are
opposite and there will not be large length changes in these muscles.
Obviously, single joint muscles will have large length changes, being
stretched or shortened during one phase or the other. In terms of control
issues, I believe that the idea that uniarticular muscles produce most of the
work and biarticular muscles control direction to be an over-simplification.
Certainly, biarticular muscles can assist in direction control but
uniarticular muscles at each involved joint can also contribute to direction
control. By remaining nearly isometric and near their optimal length
biarticular muscles can produce large forces throughout the jump. The
uniarticular muscles lose force producing ability during the propulsive phase
due to rapid shortening (loss of force due to velocity effects) to short
lengths (loss of force due to length effects). The stretch of these muscles
helps to minimize these force losses to maximize work done. In terms of
muscle or internal work, a shortening muscle clearly does more than a
near-isometric muscle. However, if you consider work at the joint or
external level, a muscle that is nearly isometric and thereby producing high
force/torque during a change in joint angle is, in fact, producing a large
amount of external work (and contributing to jump height) even though it is
not shortening. In contrast, a shortening muscle acting on the same joint
may contribute very little to external work due to low force throughout much
of the contraction.
Regards,
Warren Darling
____

_____
Andre Rodacki replied to Warren:

Dear Warren:
Thanks for your interest shown on the question I have recently posted. I
agree with your statements about the changes in muscle length of mono and
biarticular muscles. You mentioned that .
My question is: Why do you believe that uniarticular muscles can assist the
control of the movement? As they are normally found to be shortening over
their entire range, it is inevitable to ask: How and to what extent do they
would help with the control of the external force?
________
Warren Darling replied to Andre Rodacki:

It is the combination of torques exerted at multiple joints that controls the
direction and magnitude of force application by the foot. Such joint torques
depends on forces that develop in both uniarticular and multi-articular
muscles. For example, gluteus maximus acting at the hip creates
posterior-directed forces by the foot as does soleus acting at the ankle -
both are uniarticular muscles.

Some comments to these questions:
The uniarticular muscles are generally found to shorten much faster than
biarticular muscles and consequently would have less (or no) time to exert
any control over the movement (distributing moments around the joints) than
the biarticular muscles. Yes, uniarticular muscles will shorten much faster,
but how does this reduce time to exert control over the movements? The
duration of the movement is what determines the time available for control,
not the speed of shortening of the muscles. Multi-articular muscles can
certainly distribute moments about multiple joints but the actions of
uniarticular muscles can affect other joints due to inertial torques that
they create as segments move. Clearly, this is a very complex issue and it
is unlikely that simple generalizations will provide all the answers.

Warren Darling
____

__________
At Hof replied:

You should know that Van Ingen Schenau has quite drastically changed his mind
on this problem after the above papers. This can be found in the (posthumous)
paper:
Bolhuis, Gielen and Van Ingen Schenau: Activation patterns of mono- and
biarticular arm muscles as a function of force and movement direction of the
wrist in humans. J. Physiology 508: 313-324 (1998).
This remains a very interesting problem.
Yours,
Best wishes,

At Hof
Department of Medical Physiology &
Laboratory of Human Movement Analysis AZG
University of Groningen
Bloemsingel 10
NL-9712 KZ GRONINGEN
THE NETHERLANDS
Tel: (31) 50 3632645
Fax: (31) 50 3632751
e-mail: a.l.hof@med.rug.nl

__________
Stephen Levin replied:

Dear Andre,
An isotonic muscle is not recorded by an EMG (the muscle 'tone' of a resting
muscle is not recorded, no matter how tense it is). If the muscle is isotonic
when it functions then the tone of the muscle may be a significant factor in
the function without any EMG evidence of activity. If a biarticular muscle
crosses joints that are reciprocal, say the hip and the knee, so that the
muscle remains isometric and isotonic then there will be no EMG evidence of
function even though it is functioning optimally and most efficiently. Since
this is the most efficient use of muscle then evolution should dictate
biarticular muscles would operate this way as much as they could when
walking, running, biking, etc.. Monoarticular muscles would be the push to
get the joints moving. What do you think?
Steve
smlevin@erols.com (Stephen Levin)

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