Forces in the Gallop
The center of gravity is “C” and the effective forward or backward force is “C F. ” “P” is for paw and “C” is for center of gravity. When the paw is on the ground behind the center of gravity as in drawings 1 and 4, the paw is giving a forward push as indicated by the resultant force “C F.” When the paw is on the ground in front of the center of gravity, the resultant force is toward the rear (DECELERATING the dog) as shown in drawings 2 and 3. These results were proven in Pressure Plate* tests.
Pressure Plate tests prove that during gait cycle forward speed of the body is not uniform, even though variation is not visible to the eye.
At the gallop of any dog, the rear paw must be on the ground in front of the center of gravity (a point about in the middle of the chest) before slow down forces develop. In the gallop, approximately 90% of time a rear paw is on the ground behind the center of gravity, and is delivering a forward thrust about 90% of the time. The front paw is behind the center of gravity only about 10% of the time, and is delivering a forward thrust only 10% of that time proving the old saying that the rear delivers the drive and the front supports the dog is true.
When considering the total energy expended (work done), it takes energy to overcome either negative or positive pressure as recorded on a pressure plate. The total energy expended is in proportion to the sum (not difference) of the positive and negative forces exerted by the paw. Negative forces increase the energy expended and decrease efficiency.
The dog’s front paws carry the extra weight of the head and neck located in front of the shoulder. In theory and fact, the front paws not only carry the greater percentage of the vertical weight but also are responsible for stopping the greater percentage of the downward force due to downward momentum. Tests prove that the front absorbs nearly 3/5ths of the dog’s downward force while the rear absorbs only 2/5ths. For this reason the front foot is always larger than the rear front by about the same proportion.
* Pressure Plates were developed (early 1980s) for quantitative gait analysis. They measure the forces applied by a foot in any direction at any instant of time.
Find “Dog Locomotion and Gait Analysis” by Curtis Brown in List of Books.