Seems to be the current thinking. However, it doesn't take the individual into account in that some just have a bigger engine. I.E. heart and lungs and subsequently are born for the long run.
The example was driven home years ago with Duffy a Springer, could go all day and never had another Dog make him hit quit and a few tried. Developed a cough and I eventually took him to the Vet who did chest x-rays. He is a cool guy and dedicated hunter. They were thrown up on the screen and he said "Look at this!!!!" "What, something wrong?" "No, his heart and lungs are just huge."
Turns out the cough went away, but the question of why he didn't know quit was answered. Hunted hard and slowed down only little into his 12th year.
