Colleagues working in the equine field will fully appreciate the importance and relevance of conformation in horses with reference to their chosen sport, as well as their athletic performance. Dogs are the species with the largest variety of structure on the planet. Many breeds were designed with a specific purpose in mind, however each breed has structural strengths and weaknesses that owners, handlers and veterinarians should bear in mind in order to maximise these dogs’ functions throughout their lives.
Overall body size and shape play a significant role in canine performance. Dogs with a heavy structure are slower to accelerate, turn and decelerate than lighter bodied dogs but they have more power for jobs which require pulling, or supporting a physically challenged human. Imagine a Bull Mastiff catching rats in a factory or a Yorkshire Terrier apprehending a poacher!
Two important considerations exist namely, front limb structure and rear limb structure. Bearing in mind the mechanics of motion, the way in which the bones of the legs articulate largely dictates how much reach, balance and stability a dog will have when he moves.
Front Limb Structure
Much of a dog’s athletic ability is a function of the structure of its front legs, which help the dog stride forward efficiently and effortlessly, yet turn quickly and accurately when necessary. The front legs are attached to the dog’s neck, spine and ribs only by muscles and tendons. These soft tissues give the dog the flexibility to take long strides with the front legs, to abduct the front legs to help the dog turn tightly, and to lay the front legs back against the sides of the body if necessary in jumping. The disadvantage of this flexible attachment is that the softer muscles and tendons can suffer strain under pressures that would have little effect on bones.
One way to assess a dog’s front limb structure is to measure its angulation, which refers to the degree of bend at the shoulder joint (where the scapula and humerus meet) and at the elbow joint (where the humerus and the radius/ulna join). These angles provide levers upon which the muscles exert mechanical forces to drive the dog’s body forward. Dogs with well-angulated front limbs can unfold those angles to reach far forward and push well back. Thus, the angulation of the front limb partially determines how much ground a dog can cover with each stride. This is important because the fewer the steps a dog takes, the less energy is required to get from A to B.
Front limb angulation is determined by both the scapular angle and the length of the humerus. Well-angulated legs also provide more shock absorption for the dog’s weight. Dogs with straight front legs or so-called upright shoulders (< 30°) tire more easily during exercise and are more susceptible to shoulder, elbow and carpal (wrist) injuries because of increased concussion on the joints of the leg.
Rear Limb Structure
The rear legs are attached to the backbone via the pelvis, an H-shaped bone that acts as a frame to support and separate the rear legs. The hind limbs provide much of the power which drives a dog forward. With a dog in the position described above draw imaginary lines as shown in the diagram. The degree of rear limb angulation varies depending on the breed. Chow Chows have more upright hind limbs whilst Boxers are more angulated. The straighter the hind limb, the more stable the leg. Dogs bred for guarding often have more upright limbs which are very stable. Being able to stand their ground is an important part of their function. More stability also translates into an ability to make sharper turns. Irish Setters have abundant rear limb angulation which enables them to cover more ground with less effort (a desirable trait for a gun dog). However, more angulated hind limbs are less stable. This is a trait seen in modern German Shepherd Dogs with a sloping pelvis and severe hind limb angulation. This combination enables fast movement over the ground but at the expense of manoeuvrability. The instability makes tight turns difficult.
From this brief discussion it can be concluded that the desired conformation and limb angulation depends on the function which the dog must perform. An understanding of the impact of form on function, as well as an evaluation of the limb angulation, will enable a veterinarian to predict areas of weakness in an individual dog. This information can be relayed to the client and preventive measures can be taken or a conditioning program can be put in place.
Diagrams taken from The Agility Advantage Chris Zink Clean Run Productions