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> I certainly would not disagree with the first sentence. However, where does
> that leave me? How do you do you measure dynamic fit? Wouldn't static fit at
> least give you a starting point?
>
> Duncan Fletcher
> dfletche@gte.net
>
> -----Original Message-----
> From: Lauren Horn <fourhorn@fea.net>
>
> >My saddle is made by a saddle maker that believes a saddle should fit a
> >horses back when he is in motion, not standing still. Horses' backs
> >raise when they move out. I follow this type of thinking and so I don't
> >believe in the saddle tech guage.
> >
> >Lauren
> >
>
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For my senior design project in Ag. Engineering Technology at Cal Poly,
I researched, designed, and built a saddle which incorporated an "air
ride" suspension system to isolate some of that bouncin' around our poor
backs tolerate. Anyway, the project's requirements included extensive
research (literature review), and so here's a summary of some of the
information I found on the dynamics of a horse's back. If anyone needs
references, ask... just give me a few days, as I am as busy as a
one-legged dog with fleas right now.
I'm going to start with a quick anatomy lesson so that the back's
dynamics can be explained a little more smoothly later on.
A horse has 18 pairs of ribs, each meeting a vertebra along the spine.
The first ten pairs of ribs (from the front of the wither towards the
rear) are connected on the bottom to the sternum. These ribs are
usually called "sternal" ribs. The next seven ribs are called
"asternal", as they are not connected to the sternum at all (cartilage
support). The last, or 18th rib is called a "false rib". The vertebrae
meeting these ribs are called the "thoratic vertebrae", abbreviated "T1"
through "T18" (depending on their location... T1 starts the formation of
the wither, while T18 is the vertebra meeting the false rib).
The next set of vertebrae beyond the thoratic are called the "lumbral
vertebrae", and are abbreviated as "L1" to "L5". The set of vertebrae
after the lumbral are the sacral vertebrae, represented with an "S",
then caudal, with a "C", forming the tail.
Basically, the skeletal system has only about 2 inches of lateral (side
to side from a top view of the horse's back) movement from behind the
wither until you reach the last thoratic vertebra (T18). How do you
find the last thoratic? Just feel out the last rib, and follow it to
the top of the spine. When you walk your horse and look back, the back
is relatively "stiff" until that point. You will see "some" movement,
but I'm only getting into the skeletal, not muscle systems with this
post.
Then, many horses will have quite a bit of lateral movement between the
last thoratic (T18) to the first lumbral (L1). Those folks who have OF
saddles or long-barred saddles on Arabian horses may discover a problem
in this region with rubbing, as they are missing a vertebrae.
Short-backed, non-Arabian horses can also have these problems. The long
bar or panel interferes with the horse's movement, causing a "sore
loin", rubbed hairs, or ???
(As a side note: Now I'm not trying to bad-mouth OF, but I am not quite
convinced that their older saddles with the long bars were capable of
handling this kind of motion while the rest of the back (behind the
withers towards the last thoratic) was resisting. I haven't kept up
with the new stuff from this company, so I don't know if they ever
offered a "short" panel or not.)
Other areas of lateral movement are between the first three lumbral
vertebrae (L1, L2, and L3), and at the lumbral-sacral junction (last
lumbral vertebra and first sacral). Any restriction to these areas of
movement will also cause sores. The total amount of lateral movement
from the last thoractic to the lumbral-sacral region can range between 4
to 6 inches, on the average. Your own mileage may vary, but this is
what the researchers settled on.
When the horse trots or canters, the tightening of the longissimus dorsi
and psoas minor muscles will restrict the amount of lateral movement.
So, if you want to judge the amount of lateral movement your horse is
normally capable of, watch him or her at a walk.
I am not familiar with the "saddle tech guage" referred in the past
posts, but if I was going to have a saddle made with a rigid tree, I
would:
1. Measure the distance of the back which the bars of the saddle
should begin at the front to "before" the last thoratic vertebra. I
would not want the rear portion of the bar to dig into the back at the
T18/L1 junction.
2. Make sure that the distance between the two bars of the saddle (if
looking on the bottomside of the saddle) are not so narrow where they
will rest on any part of the vertebra itself. I have no problems with a
four inch or so spacing on the western saddles. Some english saddles
cut this distance very close, and on my QH cross, actually rests on the
"wings" of the vertebrae.
3. Of course, the spine will need a clear "airway" along it's length,
and the height of the withers need to be accounted for. I don't know
about endurance saddles (I prefer western), but I like at least a three
finger gap of space between the top of the wither to the bottom edge of
the fork (pommel) on a front view... but hey, I do a lot of roping
too!
4. The seat should position the rider right behind the withers (no more
than 4 inches behind the end of the wither). The horse's strongest
weight bearing area is from just behind the end of the wither to the
T10, the vertebra meeting the last sternal rib. It gets weaker beyond
that point, but can still carry a significant amount of weight,
depending on the horse.
I kind of blasted though this, but if something's not clear, I'll try to
explain myself better. My grammar goes to pot when I'm posting to the
list.... As a side note, the design project saddle did isolate the
bounce at the trot (2 to 3 Hz stride frequency), but needs a lot of work
in the "comfort" and "exterior design" department!
Kim
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