Mechanics of
Movement
Part 2
At the gallop, and in jumping, the
rear stride must generate as much power as possible to propel the
dog as far and as fast as possible. This is a gait of maximum
exertion and stride length. To achieve this, the body folds up,
roaching the spine and bringing the pelvis as far under the torso as
possible. This allows the hind leg to reach forward well past the
center of gravity (Fig 1). If the pelvis is set on too flatly or too
steeply, its ability to smoothly fold under will be disrupted. The
dog also lowers its centre of gravity - the faster the gallop, the
lower it goes. This lowered profile helps to reduce wind resistance
and makes quick turns easier, much like a racing car. The hind leg
in the support position must contract far more at the gallop than at
the trot, in preparation for a huge backward thrust, and lowering
the body enables this to occur as well (Fig 2). This is why under
angulated dogs who cannot show a roomy trot can still demonstrate an
impressive gallop. They achieve the angulation required for thrust
by dropping the entire body low to the ground. The overangulated
dog, on the other hand, cannot achieve good speed at the gallop.
Such dogs are usually too long and low stationed to begin with, and
dropping any lower would simply cause their excessive angles to
collapse under them. So the thrust they produce at the gallop isn’t
much greater than the thrust produced at the trot, and neither is
the speed. Needless to say, they are not capable of really high,
powerful jumping either.
  
At both the gallop and in jumping,
unlike at the trot, the rear thrust of both hind legs is generated
more or less simultaneously; the legs tend to move together. Whereas
at the trot the pelvis remains relatively stationary, at the gallop
it moves in concert with the hind legs. So too does the spine. As
the legs thrust backward, the back straightens out like a strip of
steel that has been bent, and then springs open, flattening the
pelvis with it (Fig 3). This is why the normal orientation of the
spine must be straight. If it is roached, it won’t have the ability
to straighten with real power. Much of the power and length of the
stride at the gallop is generated in the spine, as one can see in
cheetahs and greyhounds, whose backbones show huge degrees of
flexion. The spine may even, at the point of follow through, arch in
the opposite direction, allowing the hind legs to be thrown back
virtually level with the line of the body as it sails through the
air.
Because the gallop generates extreme
speed, the dog will expend as much energy as possible. It is not
intended as a long distance, conservative gait. The dog is going
flat out in pursuit of some wanted goal, whether it be a ball, a bad
guy or escaping livestock. At the end of the stride, at the point of
maximum exertion, the hind legs will describe a straight line from
hip to toe, with no stored energy remaining. The follow-through will
throw the legs upwards almost in line with the body, with everything
the dog has surging in one line of progression. This is when the
dog’s quality of muscling and conditioning, far more so than at the
trot, becomes apparent. It’s worthwhile if you get the opportunity
to run your hands over a racing greyhound, to get a sense of what
professional conditioning feels like. The mental component is also
necessary however. No matter how physically perfect, if the dog
lacks the mental commitment and drive for a goal, what Thoroughbred
breeders call heart, its physical abilities will remain untapped.
The back, whether at the trot or the
gallop, must transfer the power generated by the hindquarters
forward, must add its muscular effort to the generation of stride
and power, and must also support without buckling the entire weight
of the dog across each period of suspension. It must withstand the
stress of twisting and turning, the compression impact of sudden
stops, jumping and landing and, in bitches, the added burden of
carrying a litter. It should be obvious that faults of back
structure should be considered serious. In wild canines there can be
wide variations of size, proportion and angulation, but I have never
seen a wolf, coyote or cape hunting dog with a roached, swayed or
tilted (to the front or back) backline.
Power
generated in the rear and transferred along the spine must be
supported and maintained by the forehand. However, the dog’s front
doesn’t just passively carry the weight of its front half. It must
be able to absorb the energy generated from the rear without
dissipating or interfering with it. It provides the brakes and the
steering, and even generates a degree of propulsive power of its
own. The length of stride of the forelegs must match the length of
stride of the rear legs (Fig 4). Each front leg must be able to
reach as far forward as each rear leg, as well as drive back and
follow through to the same degree. To do this, the dog must posses a
well angulated shoulder blade and upper arm, as well as a high, well
muscled wither to provide leverage and a wide bed of muscle for
effective rotation of the scapula blade. Both front and rear paws
must strike the ground at the same angle, for the degree of impact
to match. They must show the same amount of contraction in the
support position and the same degree of follow through. Without an
excellent front, the dog won’t enjoy the advantage of an excellent
rear.
While much is usually made of the
necessity for a good shoulder, excellent withers are often
overlooked. High withers provide the attachment for a good shoulder,
and enable the blade to move sufficiently far forward and backward
for the foreleg to show good reach and follow through (Fig 5). As
well,the broad shoulder attachment provided by a high wither means a
wide harness of muscle about the dog’s forequarters, literally a
sling in which the full weight of the dog’s front half is carried.
In jumping, this sling must catch the dog’s total weight, and absorb
and distribute it evenly. When the dog stops suddenly, it jams its
forelegs into the ground to brake itself. If turning abruptly, it
does the same and then vaults its weight in the desired direction
(Fig 6). In both cases, the shock is directed through the shoulder
blades, into the withers and along the back. Other species which
specialize in jumping and maneuverability, such as impala and
pronghorn, show long, high, powerful withers. The broad muscling
provided by high withers is also carried well up into the crest of
the neck, and provides the foundation for the power a dog needs when
driving into the grip (Fig 7). The hyena, probably possessed of one
of the most powerful grips in nature, isn’t so much an animal with a
disproportionately small hindquarter, as one with massive jaws,
skull, neck, withers and shoulders, all supporting the incredible
bite pressure it is able to generate.
  
Good
reach and support is also aided by a good prosternum, that point of
bone (actually cartilage) in the center of the dog’s forechest. To
this process is anchored a fan of muscles that spread up either side
of the neck and pull the head down, and across both points of
shoulder and the upper arms (Fig 8). These muscles draw the shoulder
joint and humerus forward, and the foreleg inward, and are part of
the sling that supports the weight of the chest. Better leverage is
achieved when the point of sternum is positioned slightly ahead of
the point of shoulder, as seen from the side (Fig 9). That way, the
prosternum can better act as a guide when drawing the shoulder
forward, especially at the trot. At the gallop, the dog throws it’s
entire fore assembly forward well past the sternum, with reach that
is much higher than we want at the trot. It uses a great deal of of
energy, but it achieves a huge stride (Fig 10). Too much prosternum
makes the dog’s chest appear to protrude, and interferes with its
ability to maneuver sideways. This sort of structure seems to go
hand in hand with chests which are far too deep and narrow, more
like the keel of a boat, and a hindrance to agility.
 
When
viewed from the front and rear, the stride should give the
appearance of single tracking, with the paws converging towards the
centre line of the body while the legs remain relatively straight.
This requirement shouldn’t be taken too literally however. First,
the leg which is in contact with the ground, supporting and driving
the dog’s weight, should be as straight as possible from the
shoulder or hip to the ground. Any tendency for the joints to buckle
or twist both waste energy and greatly increase the leg’s
vulnerability to injury. The other leg, the one moving ahead, need
not be totally straight. This leg is bearing no weight or stress. In
fact, the contraction of the leg whether front or rear, while being
lifted bunches the muscles and will tend to bring the leg away from
the center line. The more heavily muscled the dog, the more this
tendency is apparent (Fig 11). Too much emphasis on a precise,
single tracking gait will produce animals with flat, thin muscling
and narrow bodies, as has already happened in some show lines.
Single tracking is really just an
impression given by the convergence of footsteps towards the center
line of the body. The animal doesn’t really walk with its footsteps
falling along a single line, like a tight-rope walker. In fact, the
GSD when moving correctly at the trot actually triple tracks (Fig
12).

True single tracking would require
the stride to be so short that the footstep of the rear fell short
of the footprint of the front, a gait typical of many terriers (Fig
13). Double tracking appears when the dog either moves wide in both
front and rear (Fig 14), or shows a crabbing action, with front and
rear single tracking on separate paths (Fig 15). Triple tracking,
while it may sound bizarre, actually allows a long overreach of the
rear past the front, without necessitating a crabbing action, as the
three lines of progression are very close together and to the centre
line of the body. For instance, the right front foot may travel its
own path, the left front and right rear feet will track the same
center line, and the left rear foot will follow the third path. In
this case, the dog’s rear end will be slightly shifted to the left
(Fig 16). The pattern may be reversed and the dog’s rear shifted to
the right. Interestingly, the Belgian sheepdog standard recognizes
this when it states that the dog, at the trot, shows a slight
tendency to move in a wide arc to the left or right, rather than in
a perfectly straight line. The lines of progression are barely a
paw’s width apart, only enough to allow the feet to pass each other
without interference, and one must look very, very closely to see
that the body itself is a degree or two off the straight. Without
the ability to triple track, the dog cannot achieve the length of
stride required for the flowing, effortless trot that is so unique
to this breed.
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