Compensation

It’s winter here and we are having our first days of true winter temperatures.  While outside this morning with two of our dogs, Maggie the rescue dog and Elvis, our old man, I found myself watching them gait around the yard.  With their short hair I could clearly see how they each used their fronts and rears and was able to make several observations.  Elvis, though longer bodied, has an easy-going, ground covering stride, while Maggie has a gait that covers ground, but seems to slap it at the same time.   Our yard is not the only place you can see the differences in structure and movement.  This year at Montgomery you could see many examples. 

In the years immediately following Mick’s success in the ring, you saw lots of shorter backed dogs with lifting fronts and over driving or worse, kicking rears.  Nobody thought this was ideal. As breeders continued to breed for the shorter back, sometimes to the exclusion of the overall balance of the dog, you began to see a modification of the front assembly to compensate.  This modification resulted in dogs that sometimes move in a balanced way, but have upper arms often more than 20% shorter than the shoulder blade. If you watch dogs with this structure move, focusing on their fronts, you see more movement coming from the elbow than the shoulder, and a slapping of the ground or pounding.  This is often mistaken for powerful movement.            

The ideal Kerry Blue  Terrier will move smoothly, powerfully, and effortlessly.  Reach and drive in the perfect movement will be ideally balanced front and rear.  The rear foot will touch down in the exact spot the front foot has just occupied.    The Kerry Blue Terrier standard calls for “well laid back shoulders” and the shoulder blade and upper arm to be of the same length.   The upper arm is the half of the front assembly that has all too often been overlooked by breeders. It is one of the most misunderstood and ignored parts of the canine structure yet plays a critical role in locomotion. Among many novices and veterans alike, the importance of the upper arm’s position and length is not a consideration.  More attention is directed toward the importance of the length and position of the shoulder blade.

When gaiting, the  front assembly determines the amount of reach a dog will have.  There will not be excessive kick up in the rear, nor much vertical movement front or rear. From the side, the dog will appear to flow forward with long, effortless, smooth strides. The reach and drive between the front and the rear, should be balanced.  An optimal front reach would show extention nearly to the tip of the muzzle and foot fall at speed, would be near the point where the muzzle and head meet (stop) or at the jawline. A correct front structure will result, at least partially, in clean, correct and efficient front movement.  Front movement is also determined by length of body and the balance, or similarity, between the dog’s front and rear angulations. With the shorter backed dogs, to attain this necessary balance, the upper arm in our breed has become shortened.  This allows the dog to move with the appearance of a balanced front and read, but also causes the lack of an overall powerful gait as called for in the standard.

The position and length of the shoulder blade effects the direction the force generated from the rear assembly is applied.  The length and position of the upper arm effects the reach, support, and shock absorption capabilities of the front.

Diagram 1

Diagram 1, represents a correctly balanced front assembly. As required by our breed standard, the upper arm and shoulder blade are of the same length. Notice the change in the illustrated position of the upper arm at rest (Center) and when it is at maximum reach (left). If you placed an imaginary horizontal line through the point where the upper arm and shoulder blade attach, the changing positions of the upper arm could be gauged. At rest, the upper arm would be positioned approximately 45 degrees below this horizontal line. At maximum reach, the upper arm becomes nearly vertical. Because the upper arm does not extend much past its vertical position at maximum reach, it has caused some breeders to erroneously conclude that the upper arm does not affect forward reach. This is clearly not the case.

There are three negative impediments to movement that a dog is constantly battling. The first two are inertia and friction. The third is gravity. Inertia and friction are the two that resist a dog’s efforts to move. Inertia is encountered when the dog initiates movement and when there is a change in speed. Friction occurs with every step when each paw contacts the ground and from the displacement of air as a dog’s body moves through it. These two impediments to movement are directional. Their efforts are always directed against the direction of travel. In order for movement to occur, the dog needs to supply enough energy in the direction of travel to overcome the resistance inertia and friction creates. Gravity is a force that dogs are constantly battling whether moving or standing. It too is directional in its effect, and a dog needs to constantly provide  sufficient energy downward in order to remain standing or moving. It is very important to fully understand the impact these obstacles to movement make, and the directions they effect. When looking at diagram (2, 3, 4 and 5), the horizontal line, defined by the 0 and the 180-degree marks on each end, represents the line on which inertia and friction resists movement.  Depending on whether a dog is moving forward or backing up, the direction of resistance changes to oppose the movement. The vertical line, defined by the 90 and the 270 degree marks on each end, is the line on which gravity resists support. Unlike inertia and friction, gravity’s effect is always downward. These two directional impediments to movement intersect to form a 90-degree angle as defined at point (C). Since a 45-degree angle perfectly bisects the 90-degree angle formed where these two lines meet, it is often the angle recommended for the shoulder layback because it equally divides the energy generated by the rear assembly. This equally directs the energy toward the support and forward movement functions of the front.

Diagram 2

In deterimining the importance of the upper arm, it is the amount of energy the upper arm directs toward the forward movement and the support functions of the front that matter most. 

Since the shoulder blade (B,C) and upper arm (A,C) are of equal length, a circle makes a good base for explaining and demonstrating front angulation. Mathematically, a shoulder blade set at a 45 degree angle is the most efficient for redirecting the energy supplied by the rear. In addition, if a dog’s front is set up properly, the top of the shoulder (B) will be directly above the elbow (A). Because of this, the upper arm will be set at a 45 degree angle below the horizontal. The sum of these two angles is 90 degrees. Since points (A) and (B) represents the top and bottom of the dog’s body, they also represent the upper and lower limits for the shoulder and upper arm lengths. As the angles of the shoulder and upper arm increases from the horizontal, their lengths must decrease if they are to remain equal in length as required by our standard.

In diagram (3), a modified version of diagram (2) has been superimposed upon the front assembly. The blue line segment, from point (C) to point (A), represents the position of the correct upper arm at rest. The line segment, from Point (C) to point (E), represent the position of the correct upper arm when fully extended. Point (A) represents the center of the elbow when the dog is at rest. Point (E) represents where the elbow ends up when the upper arm is fully extended. The black curved segment, from Point (A) to point (E), represents the path the elbow takes from rest to full extention. The orange segment, from point (D) to point (A), represents the distance the upper arm effects forward motion or reach. The green segment, from point (D) to point (E), represents the upper arm’s effect in the support of the front. In other words, this segment measures the kinetic energy directed downward in the front’s constant battle against gravity.

Diagram 3

As you can see, diagram (3) is not an exact fit. The differences are simply the result of the shoulder blade being tilting up and forward when extended. Since we are only concerned with the function of the upper arm, the shoulder blade’s effect has been negated.

 In the diagrams (4 and 5), two upper arms of different lengths are depicted. Diagram (4) shows the effectiveness of an upper arm of correct length. Diagram (5) shows the effectiveness of an upper arm with a 20% decrease in length. By comparing the effects of the long and short upper arms depicted in the diagrams, it dramatically demonstrates how subtle differences in upper arm lengths, have a huge impact on the effectiveness of the front’s support and forward movement functions.

Just a 20% decrease in the length of the upper arm, reduces the upper arm’s effect toward forward movement by 50% and it also reduces the upper arm’s effect toward support by 72%. The difference in the lengths of the orange segment, from point (D) to point (A), depicted in the diagrams, clearly demonstrates the negative impact a shorter upper arm has on forward movement. Also, the difference in the length of the green line segment, from point (D) to point (E), depicted in the diagrams, shows how much the shorter upper arm negatively impacts the support function.

Another very useful task the upper arm performs is being the dog’s main shock absorber. When a dog jumps, the front paws are the first to hit the ground. The upper arm absorbs the main jolt of this impact as the elbow travels backwards. An analogy to this would be a shock absorber on a car. An important aspect to some shock absorbers is their stroke length. In other words, what is the distance the shock can be compressed before it bottoms out? The same thing holds true for the upper arm. The longer the path that the elbow travels, the greater its length to be compressed. The capacity to absorb shock is greater for the upper arm depicted in diagram (4) because the elbow can be compressed further before it bottoms out. For an all purpose working breed, as was the original function of the Kerry Blue, shock absorption is very important. This is especially true for dogs competing in agility or flyball. The shock absorption qualities of the upper arm may well determine the utility life span of many of our performance dogs. It may explain why some dogs break down in the front.

Diagram 4
Diagram 5

From the epidemic of short upper arms that plague our breed today, it is apparent that the upper arm’s important functions are not being addressed.  Furthermore, the emphasis on an overly short back has brought many breeders to accept this upper arm modification as the normal construction of the Kerry Blue Terrier. 

It is very clear that the upper arm plays a large role in the correct function of the front.  Since subtle changes in the length of the upper arm have large implications on the front’s ability to function, it is important that the upper arm and the shoulder blade are given equal consideration when breeding dogs.   The longer the upper arm, the better the reach, regardless of the length and lay of the shoulder blade.

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