Equine Conditioning Plateaus?

[Bruce Murdock <bmurdock@cyberhighway.net>]

Human athletes often experience "plateaus" during their conditioning efforts, where their rate of performance increase levels off. My question is do our horses typically experience the same leveling period? 

This weekend I was reviewing my notes from our last several months, and noticed that Star's speed has steadily increased over the various sections of our usual conditioning course, and the rate of increase has been fairly constant during that period. Her heart rates have remained pretty constant all along. I have been expecting a leveling off a some point, but don't see any indications that it might be happening. I am reasonably sure (as I can be with this horse) that there has to be a "peak". Judging from my experience with her I would guess she isn't close to that point. I just don't know what to expect. 

Any thoughts, ideas, opinions?

Thanks

Bruce & Star (Save the fancy walk for later, I want to canter)
Emmett, ID