No announcement yet.

Re: inverse dynamics

This topic is closed.
  • Filter
  • Time
  • Show
Clear All
new posts

  • Re: inverse dynamics

    Dear all,

    I think Pat Riley has had a touch too much Christmas spirit! This
    discussion actually started on BIOMCH-L - to recap, it sort of went:
    centrifugal force -> end-point hypothesis -> inverse dynamics. I'm not
    complaining - this is turning into a classical BIOMCH-L debate a la
    Woltring. Sorry for the cross-posting - and I suggest we keep the debate
    on BIOMCH-L after this.

    As it happens, I'm a bit of fan of megaliths, and a member of the
    archaeoastronomy group at the University of Maryland
    and I have to say that we
    don't really know how much the builders of these extraordinary monuments
    knew about physics. I suspect it was more than we think, and I do know
    that we haven't been to the moon for a generation - I'm not entirely
    sure that we will ever manage to go back there. After the quite
    embarassing series of Mars missions, with one crash due to incorrect
    conversion of inches to millimeters, I agree with Pat that we are in no
    position to be complacent about the state of our engineering skills -
    this from an Englishman, who can't even build footbridges or run
    railways anymore

    My point about the segmental accelerations was simply that Ton and Paolo
    had discussed the problems of measurement in non-inertial frames, and I
    wondered how the nervous system copes with this problem since whilst we
    have (perhaps) joint position/velocity sensors, we have no natural
    segmental accelerometers. Ton responded that, although we don't
    conceivably possess segmental acceleration receptors in the limbs, we
    have one in the head. I confess I wasn't really convinced by this reply
    - it seems to place a lot of reliance on one sensor, and people with
    vestibular disorders, whilst clearly inconvenienced, aren't as disbleed
    as you'd expect if the vestibule were so vital.

    So, we are left with the original question, and now I suppose Pat and
    Anatol are both saying that the CNS doesn't use inverse dynamics. I'm
    not in one camp or the other, but I think the question gets to the heart
    of motor control. For too long people have been bluffing over this
    question - one reads, for example, in most textbooks, that the
    cerebellum is responsible for "coordination" of movements. What does
    that mean?

    What have we learned from a century of motor control since Sherrington?
    In my view (and I expect to be flamed for this!) not very much. We seem
    to be still discussing controversies that William James contemplated. I
    will go further and suggest that it is only when we engineer humanoid
    robots that we will really understand the nature of the problem. I am
    thinking of some work I saw last week from the MIT group (Gill Pratt and
    Hugh Herr) on walking robots using series-elastic actuators and
    actin-myosin machines. I know that Pat is working with this group, so
    perhaps he can tell us more?

    I'll now standby for the flames...

    Happy New Year to all BIOMCH-L and CGAers!

    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

    Clinical Gait Analysis:
    Send subscribe/unsubscribe to

    To unsubscribe send SIGNOFF BIOMCH-L to
    For information and archives: