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    Here are a few more P&Ps (which I pose as teaching propositions to
    my students) for anyone who is interested in commenting.


    14. The concept of isokinetic exercise and testing is misleading and

    Isokinetic testing, research and exercise is very popular in fields
    such as sports physiotherapy, but too infrequently do the users
    question the concept that it is impossible for any mechanical device
    to facilitate isokinetic exercise. Isokinetic (constant 'velocity')
    exercise is impossible for many reasons, the prime one being that all
    human motion begins from rest and returns to rest. In other words,
    there always HAS to be acceleration and deceleration on every so-
    called isokinetic dynamometer.

    This the more honest machine manufacturers readily acknowledge and
    they advise that one concentrates on the 'constant velocity' range of
    the device. However, injuries are very commonly associated with
    changes of state, such as acceleration or deceleration. We also know
    that isokinetic action is a rarity in any athletic activities (even
    swimming), so why does so much analysis of joint action rely on quasi-
    isokinetic devices which are very costly and highly specific?
    Another point - do the users all know if the constant velocity is
    constant speed, constant linear velocity,
    constant angular velocity, constant velocity of muscle contraction or
    what? Discuss the problems associated with the use of isokinetic
    (really, quasi-isokinetic) testing and exercise. Pay particular
    attention to its specificity of action and the effect of the
    acceleration and rate of force development (or change) phases that
    generally are ignored.

    15. The concept of isotonic muscle action is misleading and misused.

    Isotonic (same tension) muscle action is
    regarded as synonymous with 'dynamic' muscle action and casually
    applied in numerous texts as such. However, it is extremely rare
    that constant tension is ever observed in an active muscle. The only
    time when constant tension probably exists (before fatigue affects
    it) is during an isometric contraction or over a very small range of
    quasi-isometric action. The Russians prefer to use the term
    'auxotonic' and some Western workers suggest the use of the term
    'allodynamic' to describe the real situation of dynamic muscle action
    (i.e. changing muscle length and tension). Others consider it all a
    matter of unproductive semantics. What do you think?

    16. Abnormal foot pronation or supination may be misidentified as
    the primary causes of lower extremity running injuries.

    Many authorities label
    overpronation or oversupination etc as the major causes of many
    running injuries to the leg. However, running and all forms of gait,
    for that matter, involve the action of several interacting joints, so
    that it is impossible during dynamic gait to have pure pronation iof
    the foot. Depending on the runner's particular style, the action
    rather may be described as inversion or eversion (where these terms
    are NOT synonyms for pronation or supination!). Even this may be a
    serious oversimplification, since the athlete may also exhibit varus
    or valgus, plus other idiosyncrasies of joint action of the hips,
    toes and other joints. Do you consider it useful and informative to
    label leg injuries as a simple result of overpronation or

    Dr Mel C Siff
    Mech Eng Dept
    University of Witwatersrand
    South Africa

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