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    Here are a few more P&Ps for the week.

    I look forward to seeing some puzzles or paradoxes from your
    experience as well. The following are a few more of the PROPOSITIONS
    (not facts!) that I use in teaching my students. They have to
    discuss, find references or propose their own answers based on
    existing theory. Your comments are invited.


    17. Ballistic stretching may not be as well understood or as harmful
    as has been claimed.

    Ballistic stretching commonly is regarded as stretching performed
    with bouncing or with the use of momentum to
    extend one's normal range of movement. Little is ever said about the
    state of the tissues involved during the process, which constitutes a
    serious omission. The bouncing may be imposed either on relaxed
    muscles or contracted muscles, the mechanisms and results in each
    case being very different. One must also appreciate the differences
    introduced by changing the rapidity of the bouncing, taking into
    account the fact that explosive bounces on contracted muscles may
    constitute what is known as 'PLYOMETRIC' ACTION (not plyometric

    This then necessitates considering the roles played by
    elastic energy, eccentric muscle action and reflex processes. On the
    practical side, we note that ballistic actions involving both relaxed
    and contracted muscles occur all the time in most sports, in most
    cases sparing energy and improving efficiency without causing injury.
    Yet most 'experts' on stretching advise against the use of ballistic
    stretching, especially on contracted muscles. Comment.

    18. Reliance on the hyperbolic Force-Velocity curve to understand
    the relationship between training load and speed may lead to serious
    misunderstandings of strength training.

    The well-known hyperbolic F-V curve shows that FORCE DECREASES as the
    movement velocity increases and increases as the movement velocity
    decreases. Or does it show that the VELOCITY INCREASES as the force
    decreases (and conversely that the velocity decreases as the force
    increases)? Are these just inverse ways of stating the same thing or
    is one of these statements incorrect or misleading?

    Let us now take this curve out of the laboratory where it was derived
    and take it into the world of real sport where movement efficiency
    depends not only on rate of voluntary (or electrically stimulated
    contraction), but also on the storage and release of elastic energy.
    Does this standard F-V hyperbola still apply here? What about the
    force-velocity relationships in the case of cyclic versus acyclic
    activity, bearing in mind the fact that Russian scientists have found
    at least two peaks in the cyclically-produced F-V curve? Let us also
    consider the characteristics of the F-V curve when the action is
    rapidly terminating eccentric. Comment on all of this.

    19. Our understanding of bouncing squats may be incomplete or
    incorrect.Most of us have been warned about the increased patello-
    femoral force produced by bouncing at the lowest point of the squat
    and the consequent risk of knee damage (to the joint, ligaments,
    tendons etc). Elite Bulgarian lifters, however, maintain that it is
    less dangerous and much more efficient to bounce in the squat when
    one recovers from the lowest position of the Olympic snatch or clean.
    They emphasise that knee injuries are more common among powerlifters
    who squat SLOWLY to and from a HALF squat position with the aid of
    protective knee wraps or bandages, compared with weightlifters who
    bounce rapidly with unprotected knees out of a full squat, often
    producing greater reactive forces as measured on a force plate.
    Which viewpoint is correct and why?

    20. Defining isometric muscle contraction simply as a static muscle
    action is a misleading oversimplification that can confuse research
    and training.

    Firstly, do we know if the same muscle fibres producing
    the isometric contraction are exactly the same or are they rapidly
    and regularly relaxing and recruiting other fibres to maintain the
    action? Next, there is not just one type of isometric action. One
    has to take into account how rapidly the peak isometric force is
    produced, since the activation curve and effects of fatigue will be
    different for each situation. Russian scientists recognise at least
    two types of isometric action: SLOW (gradual onset) isometrics and
    EXPLOSIVE isometrics (which occurs during the coupling phase between
    the eccentric amortisation phase and the concentric driving phase in

    Furthermore, they distinguish between CONCENTRIC
    isometrics (produced if the contraction is on the point of overcoming
    a load) and ECCENTRIC isometrics (produced if the load is just about
    to overcome the contraction). We must also remember that different
    neural mechanisms are involved with motor activity at different
    speeds and that the Russians explosive isometrics for speed and power
    development. The torque (or force) - joint angle curves derived in
    the laboratory are produced under slow isometric conditions and
    cannot accurately be related to actions that involve explosive
    isometrics. Most of the studies of the effects of isometric training
    on muscle strength, power, hypertrophy and endurance have involved
    only slow isometrics. How much of our research on isometrics is then
    of definitive scientific or practical value?

    Dr Mel C Siff
    School of Mechanical Eng
    University of the Witwatersrand
    South Africa