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Re: pec tear during a 10RM bench press

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  • Re: pec tear during a 10RM bench press

    This is an interesting question and I'll offer my own
    view as food for thought as a recent listner and first time caller
    to this Biomx group....

    The question of muscle tearing can be thought of as mechanical failure of
    biologic tissue. The muscle is perhaps best modeled as a viscoelastic
    material. The question becomes, how does the mechanical structure
    of a muscle fiber change with respect to the number or work cycles.
    As the biochemical factors change, the rate of cross bridge binding
    and unbinding is believed to be constant when comparing rep # 1 to rep # 10.
    However, the material properties of muscle may show a decreased
    time dependence with increasing rep, thus the higher number the rep,
    the less 'give' or 'slack' in theory, a unit of muscle is able to perform
    as a result of either
    1. locked cross bridges (cramping, rigor mortis)
    2. connective tissue deterioration during the set (composed of repititions)
    3. a hole host of contributing factors relating to structure-function
    and physiology during contraction.

    this is a very interesting question and can be approached
    experimentally, via material testing
    or analytically through optimization design/analysis.
    or case studies of those that have torn their pecs ( which I believe
    was written in one of the muscle magazines a year ago or so)

    The importance of time dependent changes addressed the principles of
    rate of reactions, recruiting of fiber bundles, initial conditions
    of the muscle (remembering the importance of prestretching before
    exercising), metabolism of the individual,athletic condition of the
    individual, dietary input of the individual, rate of lifting,
    the amount of weight being lifted,and failure mechanics of composite
    materials should be considered to address this question fully.
    However, the model becomes complicated rather quickly and the answer
    could be found by following up some the force studies of myofibers, I
    believe by Faulkner,Brooks, and/Dennis. The drawback to single fiber
    studies is the effects of recruiting and rate of loading a whole muscle
    cannot be determined.

    The short story is the muscle unit has greater mechanical integrity
    at the beginning of the set, but can produce greater force.

    For the last rep, the muscle unit has less mechanical integrity, but
    produces less force (or does it, if you're lifting the same weight ten
    times)

    Based on this, I would say for the last rep you are producing the same
    amount of force, at a slower rate of loading, recruiting fiber
    bundles with greater frequency, but of shorter duration, causing microdamage
    within and between myofibers (muscular and connective tissue respectively
    but not exclusively) Hence, the last rep would be the one to do the damage.

    Anecdotely, I've never seen an athlete tear a muscle or sprain soft tissue
    within the first five minutes of a game, providing they have been
    educated to stretch and warm up appropriately and they weren't slide tackled
    from behind. But have noticed most of these injuries occur during the
    second half or later periods. Even if this is a question of coordination,
    the forces resulting from uncoordination are acting on a fatigues system.
    The same issues apply to the biochemical and structural effects
    of fatigue on the musculoskeletal system.


    Alexander Kazerooni, MS
    Biomedical Engineering & Kinesiology
    University of Michigan, Ann Arbor
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