Here's a little about the leg and weights, from Dr. Deb:
>>Horses are cursorial animals, meaning they are adapted for running.
One aspect of this is what is called "telescoping" of the distal limb
elements.
What this means is that the parts of the horse's limbs below the carpus
("knee") and tarsus ("hock") are proportionally much longer than the
equivalent parts in the human hand and foot, or the fore and hind paws of
bears, cats, raccoons, badgers, armadillos, elephants, etc.
Additionally in the horse, all of the muscles which operate the slender
lower limbs are packed up above the knee and hock.
What harm do weights do?
Or what effect does weighting the distal end of a horse's limb have?
Figure this out for yourself by getting an ordinary straw broom.
Use one hand to pick up the broom by the middle of the handle. Use the
muscles of your forearm to lift the back of your hand (and the broom).
Operate it like you were going to make a backhand tennis shot. You will find
that you can do this fairly easily, even though the bristles of the broom do
constitute a certain amount of weight.
The reason that it's easy is that the point of attachment of the muscles
that are operating the broom (i.e. where you are grasping it)is close to the
distal end of the broom.
Now, still using only one hand, grasp the broom as close as possible to the
end of the handle.
Try lifting the bristles the same way -- obviously much more difficult.
This is why the horse's haunch and shoulders are so very muscular.
It takes a lot of power just to move the unshod limb.
Now go out to the barn and get an ordinary horseshoe, and use some duct tape
to tape it onto the bristle part of the broom.
Once again try to lift it from the tip ....
....and of course, the last demonstration is to go get a weighted "boot" or
a heavy shoe.
Now what you have just done by trying to lift the broom is one, single,
small movement, equivalent to a horse taking one step at a walk.
At the next level, do be sure to take the horseshoes off of the broom.
....Because now you have to do the equivalent with the broom of galloping or
trotting vigorously. This means swinging it....
Here you will not only have to contend with the leverage disadvantages of
having a "telescoped" limb in which the weighted distal end is far from
where the muscles "grip", but you will also have to deal with the incredible
centripetal forces as you swing the broom like a tennis racket -- still
holding it by the tip -- which will try to jerk the broom from your grip.
I don't think it will be real safe, or actually necessary, for you to attach
the weighted boot to the broom to see what is going on, but the name of what
is going on is "jerk".
The weights have the effect of jerking on the joints. The body's response is
to build up the muscles which "feel" the jerk. In the case of the equine
forequarter, jerk from weights primarily affects the shoulder joint, which
is particularly vulnerable because, unique among all joints, this one has no
collateral ligaments, and is thus held together entirely by the overpassing
muscles.
Horses that are made to wear weighted shoes always appear to develop wide
chests --
-- but this brings us right back to the need for people to learn the anatomy
correctly, because what they perceive as the horse's "chest" widening is
actually not its chest at all, but merely the shoulders which are slabbed
onto the sides of the chest. It is the subscapularis, supraspinatus,
infraspinatus, and biceps brachii muscles which "jerk" causes to hypertrophy
.... so the shoulders thicken, and they lose range of motion, but the people
are fooled because the skin does have to stretch from one side of the animal
to the other, all the way across the front, and they think this is its "wide
chest".
Likewise weights also call on the cervical trapezius muscles (which connect
the shoulders to the neck) for greater effort, and when these hypertrophy
the people sometimes say that the horse has a more attractive neck.
It is certainly a bigger, thicker, and stiffer neck, but it is lumpy, and
the added bulk is no indication that the posture of the neck -- the way the
horse uses or carries his neck -- is correct or helpful to him.
The other thing which weights on the forefeet do is hold the horse onto the
forehand, as my many studies of published (and amateur) photographs
demonstrates.
"Lightness" means that the horse's forequarter rises with respect to his
haunches during movement; it means the animal rounds its back and raises THE
BASE of its neck.
Weights on the forelimbs make it almost impossible for the animal to
accomplish this."
