Michael, Years ago coursing blood was running through the dogs make up and they could handle heats and finals in one day...I can remember as a youngster going to All Black matches with my dad and they never came off the field.in an entire game..... Look at the poofs today ,honestly!!! Evolution has taken care of things I guess, and it can only get worse from here on in.... A caring , astute trainer can place individual dogs to perform under the circumstances and run them accordingly. I wonder though as to the astuteness of a few trainers ??