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Definition of Angonist & Antagonist

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  • Definition of Angonist & Antagonist

    Dear colleagues:

    According to the textbook I am using for my undergraduate Kinesiology
    course, 'antagnist' is defined as "the role played by a muscle generating
    torque opposing that generated by the agonists at a joint". Then it goes,
    "When a muscle opposes a movement at a joint through development of
    eccentric tension, it is acting as an antagonist." I witnessed similar
    statements in some other textbooks I happened to possess. But I believe
    there is a discrepancy between these two statements.

    The definition implies that the antagonists opposes the agonists for fine
    control of the movement and safety. When the agonists produces too much
    tension or when the joint angle reaches the extreme of the joint range of
    motion, the antagonists will produce tensions to control or slow down the
    joint motion for fine control and safety since muscles produce tension only.
    When the agonists contract concentrically, it is obvious that the
    antagonists should contract eccentrically to slow down the joint motion. So
    both statements above seem to agree. But what about the eccentric
    contraction of muscles due to external load such as gravity?

    Let's imagine some one is doing pushups. The triceps contract concentrically
    during the up-phase, but eccentrically during the down-phase. According to
    the second statement above, the triceps are the agonists during the
    up-phase, but the antagonists during the down-phase. Which group of muscles
    are the agonists in the down-phase then? Since the elbow flexion during the
    down-phase is basically caused by the gravity, the elbow flexors can not be
    the agonists. So the definition does not hold here.

    Or can we view the triceps as the agonists in both phases? The main job of
    the muscles which the man intended during the down-phase was to slow down
    the elbow flexion against the torque produced by gravity. Triceps are
    undertaking this job. When triceps produce too much tension causing too slow
    an elbow flexion, the elbow flexors can compensate that as antagonists.
    According to the same author, agonist is defined as "a role played by a
    muscle acting to cause a movement". The triceps are causing 'slow-down' of
    the elbow flexion during the down-phase of pushup. Whthout the activation of
    the triceps, he will simply collapse. If we stick to the definition, the
    second statement is incorrect.

    I'd like to get some comments or feedback on this issue from the readership.
    Anything helpful to clarify this issue will be welcome. I'll post the
    summary later. Thanks!

    Young-Hoo Kwon
    - Young-Hoo Kwon, Ph.D.
    - Biomechanics Lab, PL 202
    - Ball State University
    - Phone: +1 (765) 285-5126
    - Fax: +1 (765) 285-9066
    - E-mail:
    - Homepage:

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