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Summary of muscle coordination in SSC

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  • Summary of muscle coordination in SSC

    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.
    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)
    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.
    Best wishes,

    At Hof
    Department of Medical Physiology &
    Laboratory of Human Movement Analysis AZG
    University of Groningen
    Bloemsingel 10
    Tel: (31) 50 3632645
    Fax: (31) 50 3632751

    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 (Stephen Levin)

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