I believe there is a difference between the footfalls in 4-beat school canter (collection) and 4-beat canter - too forcibly slow and on the forehand.
The difference is in how the diagonal disassociates. The horse either lands first the back foot or the front foot of what would be a single beat (diagonal pair of legs) in the 3-beat canter.
One of the easier ways to see this is the energy - even though the school canter slows, the energy/power builds. There would not need be any re-balancing, "in-between" strides between it and extended canter (or any other movement). In contrast, the 4-beat on the forehand canter would obviously need some help before the horse could do anything else...
I don't have nearly enough (read: any
) experience with the school canter yet, but have definitely seen (and ridden
) the second kind of 4-beat canter - when the front end of the horse comes down early - the horse catches himself with his front leg, the diagonal disassociates with the foreleg hoof landing first.
So the texts say the school canter's four beats come from landing the hind leg first.
However, this brings a question... (lot's has been said about this with the "advanced placement" of competition dressage horses in trot - when the hind foot of the diagonal lands before the front...)
...doesn't this mean that the hind foot then also leaves the ground before the front? There has been some arguments that in that case it's the leg which leaves the ground last (front in this case) is the one providing the propulsion force.
I don't think I agree with this theory.... I think when the horse works in collection - longitudinally shortened from point of shoulder to point of buttock, elevated in front and lowered in the haunches, it's as if the front legs play a very minor part in locomotion, and the power comes from the hind legs. But this may be a different story with a stiff "long" horse flailing forwards....
Anyone care to comment???
Oh how I wish I had four legs for a few hours - to do my own experimenting!