The Importance Of The Upper Arm, by Steven A. Robinson

The upper arm is the other half of the front assembly that has been all to often overlooked. It is one of the most misunderstood and ignored parts of canine structure. Among many novices and veterans alike, the importance of the upper arm’s position and length is not a consideration. Much attention is directed toward the importance of the length and position of the shoulder blade, but to our canine’s detriment, the upper arm has become the forgotten half of the front assembly. I believe the primary reason for this is not having a clear understanding of its function. The purpose of this article is to provide an understanding of its function and to point out the advantages to giving this area of the front assembly its due consideration.

Where 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. Let us begin by looking at the front assembly.

This is a working diagram, diagram (1), of a correct 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 and will be demonstrated later.

Before we concentrate our focus to that of the upper arm, let us take a look at the big picture. 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 our dogs’ are constantly battling whether moving or standing. It too is directional in its’ effect, and a dog needs to provide constant 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 that inertia and friction resists movement on. 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 gravity resists support on. 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.

In determining 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 matters 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 end. 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 to make explaining more visually understood. 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 arms effect in the support of the front. In other words, this segment measures the kinetic energy directed downward in the fronts constant battle against gravity.

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.

Diagram (5)

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. In diagram (6), the effects of the long and shorter upper arm are compared.

Another very useful task the upper arm performs is being our 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 it can be compressed before it bottoms out? The same thing holds true for the upper arm. The longer the path is 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 a working breed, which is required to jump and go over walls, shock absorption is very important. This is especially true for a heavy breed like ours. The shock absorption qualities of the upper arm may well determine the utility life span of many of our Rottweilers, and it may explain why some dogs break down in the front.

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. It is very clear that the upper arm plays a large role in the effectiveness of the front assembly. 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.