I do apologise for misunderstanding, its a bit hard to keep with the different tangents you go on.
Well yes, not sure if its the same in horses (couldnt be too much different) but in humans we all rely on our anaerobic fitness when we go over 80-85% of our max heart rate.
Again the R0s going 30,30,30,31 will get the same lactic acid build up as the SBSWs going 26,27,28,28. You have to remember the R0s wont be going 26,27,30,35.