A dog is like a human.
Human who don't run often aren't going to run for a long
time.
Something for dogs. If you have a fat dog then he isn't going to
run long.
If your dog runs with you everyday and your dog is fit, then he
may run for a long time.
All depends if he/she is fit.
If you want to run with your dog for a long time, train him/she
for it.