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Re: Summer science quiz #3

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  • Re: Summer science quiz #3

    Dear all,

    Disappointing response to the bird leg quiz. Either the solution is
    obvious and I can't see it, or it has completely foxed you all. So let
    me throw one possibility into the ring to stimulate discussion.

    I wonder whether the reverse flexing joint might be for stability during
    landing. My reasoning goes as follows. Our legs are most stable when the
    ground reaction vector passes anterior to the knee joint, locking the
    joint against the posterior capsule ligaments. It is for this reason
    that we have an "L"-shaped foot (rather than "T"-shaped), since the
    center of pressure is normally maintained anterior to the ankle.

    I hypothesise that a bird's most unstable time is when it is landing,
    because there will be a sudden and large force on the undercarriage
    (legs). Since birds generally fly forwards, this force will have a large
    posterior component, which will tend to flex the leg (ankle). I contend
    that a bird evolution has reversed the leg so that it is most stable
    when the ground reaction is posterior, so increasing stability for

    Am I completely away with the birds?

    Dr. Chris Kirtley MD PhD
    Associate Professor
    HomeCare Technologies for the 21st Century (Whitaker Foundation)
    NIDRR Rehabilitation Engineering Research Center on TeleRehabilitation
    Dept. of Biomedical Engineering, Pangborn 105B
    Catholic University of America
    620 Michigan Ave NE
    Washington, DC 20064
    Tel. 202-319-6247, fax 202-319-4287

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