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Robert Kearney
06-23-1997, 12:18 AM
I am responding to Marina Koutchouk's request for information regarindg
the stiffness and dampins of different human joints posted on Frduay 20
June.

In general I thing that most of the information is simply not available.
There have been a number of single degree of freedom studies of
individual joints -- mostly ankle, finger, wrist and elbow. Ian Hunter
and I reviewed these in a CRC review in 1990.
(Kearney, R.E. and I.W. Hunter, System identification of human joint
dynamics. Critical Reviews in Biomedical Engineering, (1990) .18:55-8.).
In general these studies show that:

(1) Joint propoerties can be reasonably approximated by inertia,
stiffness and damping for small perturbations under stationary operating
conditions;

(2) However, the damping and stiffness change dramatically with the
operasting point and are particularly sensitive to changes in position
and level of activations. Stiffness changes may be greater than an order
of magnitude as these conditions vary through the physiological range.

(3) The simple second order model DOES NOT hold when these parameters
are changing rapidly as they do during active or passive movements

(MacNeil, J.B., R.E. Kearney, and I.W. Hunter, Identification of
time-varying biological systems from ensemble data. IEEE Trans. BME,
(1992) .39:1213-1225.

(Kirsch, R.E. and R.E. Kearney, Identification of time-varying stiffness
dynamics of the human ankle during an imposed movement. Exp. Brain Res.,
(1996) .In Press.

(4) Reflex contirbutions, at least at the ankle, are very nonlinear and
cannot bre thought of as simply increasing the stiffness or damping at
the ankle (e.g. Kearney, R.E., R.B. Stein, and L. Parameswaran,
Identification of intrinsic and reflex contributions to human ankle
stiffness dynamics. IEEE Trans. BME, (1997)

(5) Until now there have been relatively few studies of joint mechanics
of larger joints (hip, knee, shoulder) or multiple degrees of freedom
There is some very recent work in this direction: Gomi, H. and M.
Kawato, Eqilibrium-point control hypothesis examined by measured arm
stiffness during multi-joint movement. Science, (1996) 272:117-120.)


Hope this information helps. Please contact me if you need more
information.

rob kearney
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______________________________________
Robert E Kearney, Ph.D. Eng.,
Professor & Chair,
Department of Biomedical Engineering,
McGill University,
3775 University Street,
Montreal, Quebec, Canada H3A 2B4

Tel : (514) 398-6737
Fax : (514) 398-7461
E-mail: rob@cortex.biomed.mcgill.ca
______________________________________
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