Dear BIOMCH-L readers,

My colleague Rene van Weeren at the Faculty of Veterinary Medicine in
Utrecht (Netherlands) has recently completed his PhD thesis concerning
the effect of skin-movement in kinematic analysis of the horse. The
thesis may be of interest to those who use kinematic data for
biomechanical analysis. A number of copies is still available from the

Dr. P.R. van Weeren
Department of General and Large Animal Surgery
Faculty of Veterinary Medicine
University of Utrecht
P.O. Box 80153
3508 TD Utrecht, The Netherlands.

A short summary:

by P.R. van Weeren, ISBN 90-9003110-3

Chapter 1 is a review of equine movement analysis, and a general
introduction to the problem of skin movement.
Chapter 2 describes a technique (subcutaneous LED's) for direct measu
rement of bone movement in a walking horse. Results and regression
models relating skin movement to joint angles are presented in chapter
The LED's could not be used in the upper parts of the limbs, where the
bones are covered by a thick layer of muscles. A new technique, based
on transcutaneous pins with two markers attached, was developed.
Results for the walk and trot are presented in chapters 4 and 5. In
chapter 6, the skin movement patterns of horses with different size are
compared. It was found that, after normalization to bone length, the
time courses of skin movement in different individuals were very
An algorithm to correct raw kinematic data for skin-movement errors is
developed in chapter 7. In order to apply this method, one has to be
able to predict skin movement in an arbitrary individual. Suitable
regression models, based on previous measurements, are given in chapter
The final chapter (9) shows how the correction method can be applied
to measurements done with a (modified) CODA-3 system. After correcting
the kinematic data for skin-movement errors it was found that the knee
and tarsal joints of the horse move congruently, which confirmed the
existence of a 'reciprocal apparatus' formed by the Peroneus Tertius and
Gastrocnemius muscles. Previous attempts had always failed because of
errors as large as 15 degrees in the knee joint angle.

According to the tradition, the thesis is accompanied by a number of
'propositions', of which the first two are:

'There is a marked discrepancy between the accuracy of the equipment
used for equine kinematic gait analysis and the care with which
researchers interpret the error caused by skin displacement in gait

'The accuracy and high standard of equine kinematic gait analysis before
World War II may serve as an example to many contemporary researchers.'

--Ton van den Bogert
Dept. of Veterinary Anatomy
University of Utrecht, The Netherlands.