Thinking about biomechanics and biochemistry and dog agility
March 10th, 2010 Posted in life with poodles | No Comments »Some trainers think that a collected curved jump is better for the dog than a flat fast jump and that that’s a reason for higher jump heights. I’ve been musing on that and on other aspects of the dog’s physical health.
Newton’s first law: an object in motion stays in motion unless acted on by an outside force. An object at rest stays at rest unless acted on by an outside force.
Outside forces are friction, gravity, etc. So horizontal motion (like a dog jumping flat) is actually only subject to the force of gravity, the speed of the horizontal motion is irrelevant. BUT… the dog puts its legs down and generates propulsion (forward motion) by using its muscles. Theoretically more effort is required to go faster… but the most effort is required to stop a stopped object or stop a moving object.
Imagine a dog in a pool, for example. Its weight is supported by the water (which also generates considerable resistance, but I’m neglecting that at the moment so I can generate this theoretical construct). It can touch its legs to the bottom to move itself horizontally, but there’s no impact. That would be the zero-stress situation: not supporting its weight and using its muscles alone for propulsion.
If a dog is running fairly level (level topline, little bouncing), than the amount of impact should be minimal, and each leg as it hits would simply generate propulsion. So flat jumping would seem to be best since all that has to happen is that the dog suspends all its legs momentarily while continuing flat forward motion. It will fall somewhat during that time, and that amount of impact would have to be absorbed.
I certainly think a slow collected jump generates less impact than a fast collected jump, but I’m less persuaded that a slow flat jump is better than a fast flat jump–I just don’t think there’s a lot of difference in impact between the two.
Now, if we neglect impact and think about muscle energy, which is also a stress to the dog’s body, it definitely requires more muscle effort to move faster than slower. Biochemically, it’s necessary to generate more ATP more rapidly, for example, which also creates byproducts (lactic acid) if done anaerobically (without sufficient oxygen for full respiration). Agility runs are definitely all-out sprints for the handler and for the dog. Adequate biochemical recovery time is definitely required.


