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From: <heidi@xxxxxxxxxxxxxxx>

> <sigh>  Truman, you really do need to go back and study mechanical
> advantages of levers, etc.  I'm sure kat could give you a far better
detailed
> description than I can
While I have no desire to give a detail description of the operation of
levers in the mechanism that is a horse, I can refer anybody who is
interested to a good source.  James Rooney, DVM's book, _The Lame Horse:
Causes, Symptoms & Treatments_ is just such a source suitable for the
"lay reader."  In the preface he states, "I shall assiduously avoid all
mathematis. It will be necessary, however, to use a few vectors and a
few very basic mechenical illustrations.  It is, after all, impossible
to talk about mechanics without talking about mechanics."

The book is (as the title suggests) about how and why horses go lame
(i.e. their locomotor system breaks down in some way, and he restricts
himself to the locomotor system) in the foreleg, the rearleg and the
back.  This aspect of the book makes for a very interesting read.

However, what I found of even greater value was the way he prefaced his
discussion of all the things that can go wrong with these systems with a
description of how it is supposed to work when it is working properly.
He starts with a description of "The Normal Foreleg" and explains where
each of the bones is, their range of motion, how they attach to each
other, the tendons, ligaments and muscles that act as forces (and more
often as not opposing forces) on the levers that are the bones and how
contraction and relaxation of the muscles and the timing of these things
propels a horse forward (and keeps it from falling on its face while
doing so, which is why the foreleg is more often a brake than it is an
accelerator).

This is the best text I have ever found with respect to describing how
horses move which is with levers (bones) pulleys (muscles and their
attached tendons), and springs (tendons and ligaments and muscles) and
how it uses its own weight to propel itself forward.  There are no cogs
or gears in the mechanism that is a horse, so when a horse changes gaits
(say from a walk to a trot) it is not truely changing gears, it is just
changing the timing of its foot falls.  However, the timing of the foot
falls (and the swing phase) has an enormous impact on the amount of work
the horse must do in order to propel itself forward.

Truman is quite right about one thing, the levers and pulleys and
springs are not actually doing the work for the horse; however, they are
enabling the horse to get gravity to do some of the work for it.  And he
is quite right, the dolly is not doing any of the work for me when I
move a bale of hay, it is just making it so that gravity moves the bale
of hay for me because the path between the hay shed and the horses is
slightly down hill.

James Rooney's book does an admirable job of explaining just how this
mechanism operates normally, and even his discussion of how and why the
mechanism breaks down gives a good understanding of how it is supposed
to work.

For people who are interested in the nuts and bolts of the physics of
it, he has also written a book, _The Biomechanics of Lameness in Horses_
which goes into much more detail; however, it does NOT assiduously avoid
mathematics but rather dives right in to the nitty gritty, and,
consequently the mathematics is extremely complicated. So I don't
recommend it in the same way that I do _The Lame Horse_ which is
"designed for all readers interested in the horse and is illustrated
with more than 180 drawings, photogrpahs, and X-rays. The pony-clubber
as well as the experienced horse trainer, the veterinarian and the
novice rider may all derive both facts and ideas that should improve
their work with the horse and stimulate further thought." [From the dust
cover of the 1986 printing; although there is a new edition that came
out in 1998]

kat
Orange County, Calif.



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