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When jumping over obstacles, dogs land with significant force applied to their forelimbs. If this is an infrequent event, then the impact is usually of little concern, but repetitive jumping over many years may have significant consequences. Repeated impact loading has been documented to cause some overuse injuries in human athletes. The effects of jumping on chronic injuries in dogs has not been studied extensively. Forelimb injuries such as biceps tendinitis and carpal hyperextension (severe wrist sprain) seem to occur more frequently in dogs that do a lot of jumping. Chronic, repetitive forms of trauma, including jumping, have been linked to another type of shoulder injury in dogs termed mineralization of the supraspinatus tendon. Both the frequency of jumping and the height jumped may play a role in these injuries.
There is some concern among certain breed clubs that jump heights used in obedience competition may contribute to long term orthopedic trauma in dogs. A jump height standard of 1 1/4 times the dog's height at the withers is commonly used in competition. One potential problem with using a jump height standard based solely on the dog's height is that it does not take into effect the body weight or body conformation of the different breeds. In their recently published book, Jumping From A to Z, Zink and Daniels discuss "weight:height ratio" as a more accurate way of determining the risk of jumping. Dogs with a ratio of greater than 4 (when using weight in pounds and height in inches) are considered in the "danger zone" for jumping. They advised jumping at full height only when the footing is excellent and the landing is soft. Further concern is stimulated by the results of a scientific paper published in 1992 in Veterinary and Comparative Orthopedics and Traumatology. In a study entitled Measurements of Vertical Ground Reaction Force in Jumping Dogs, the authors found that the forces increased significantly with increasing height. Vertical ground reaction forces are considered to be an accurate indication of the impact placed on the forelegs when a dog jumps. Furthermore, the dog's body weight and breed also influenced the vertical ground reaction forces. Statistical analysis of the effect of weight on force shows that heavier dogs impact with greater force at each jump height.
Factors that may affect vertical ground reaction force were discussed by the authors and these included conformation, jumping style, degree of training and physical conditioning. Dogs with less angulation in the limbs and straighter conformation were thought to land with greater forces. It was also mentioned that well-trained dogs appear to jump and land more smoothly ("good style") than the stiff-legged landing of untrained dogs. Good physical conditioning may enable a dog to more actively control joint motion. In fact, properly timed and executed muscle contractions may provide a shock absorbing effect. Smooth landings allow the jumping dog to absorb the impact over a longer period of time than stiff landings, in which the jarring impact results in higher vertical ground reaction forces.
If jumping contributes to the development of acute and chronic injuries in a significant number of dogs, should we be taking proactive steps to decrease these injuries? It is apparent that more investigation into the long-term effects of jumping is necessary. A number of veterinary schools have canine sports medicine programs that are equipped to evaluate these types of questions. On the competitor level, one simple step might be to lower the jumping height requirement for breeds whose conformation is not well suited to jumping. As long as the changes are consistent, this would have minimal impact on competitive events and may have a significant impact in reducing injuries.
This article originally appeared in the October 1996 issue of Canine Sports Medicine Update.
