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Herman J. Woltring
06-06-1991, 09:59 PM
Dear Biomch-L readers/posters,

In reply to Karin Rosenberg's question on pelvic orientation (or attitude, as
I would prefer to call it) during stance, a very useful source is David H.
Sutherland, Richard A. Olshen, Edmund N. Biden, and Marilynn P. Wyatt, "The
Development of Mature Walking", MacKeith Press 1988, Blackwell/Oxford and J.B.
Lippincott/Philadelphia. One of the authors is a Biomch-L subscriber, and
the group is with the Children's Hospital in Frost Street, San Diego, Calif-
ornia. Some time last year, I posted a review of this book to the list (Mike
Whittle: my apologies -- I cannot seem to come around reviewing your book!).

Note that their graphs are expressed in terms of so-called `planes of move-
ment' (pp. 65-66):

"We have chosen to consider the familiar, laboratory-oriented planes
of movement used by physicians and physical therapists rather than more
complex concepts such as *Eulerian movement* which would be familiar
only to engineers, mathematicians or physicists. A brief review will be
given for readers who may not be accustomed to the terms. In the context
of the laboratory, *sagittal* movement is in the direction of walk pro-
gression and is best viewed from the side; *coronal* movement is from
side tot side and is best viewed from the front or back; *transverse*
movement is about a vertical axis and the ideal viewpoint, although im-
practical, is from above or below the subject."

" *Eulerian movement* related to the motion of each segment (rigid body)
to another or multiple other rigid bodies in space" [or to the spatial
reference coordinate system -- HJW].

Note that this approach is rather useful if the movement is the classical
paradigm of level, straight walking along, e.g., the X-axis of a laboratory-
defined, Cartesian coordinate system, for *segment* movement in particular
(i.e., segment position and attitude expressed relative to the laboratory
frame of reference). However, it is less attractive for *for joint movement*
as defined in this approach (i.e., differences of corresponding segment angles)
since these so-called `projection angles' will change even for a `fixed' joint
(unless it is in the neutral attitude, with equal projection angles for the
proximal and distal segments) if the subject as a whole -- or the laboratory
reference coordinate system -- changes orientation, e.g., by a rotation about
the vertical axis. Eulerian angles (or helical ones) do not suffer from this
disadvantage. Here, the engineers/mathematicians/physicists do have a mis-
sion, it seems.

An intermediate solution would be to define `projection plane joint angles'
as those angles where the attitude of a distal segment is viewed after re-
aligment of the laboratory reference system with the proximal segment's
coordinate system. This is, however, an interdisciplinary (`political')
compromise ...

Herman J. Woltring, Eindhoven/NL