tired dog lie

On the weekend, Milo and Pebbles get more than a bit of a workout. 
What would make them so tried? They seemed to be lying down all day.
1.Follow mummy about from day break to day's end 2. Explore areas not explored yesterday 3.Bark or chase the neighbour's dog, cat or Tex, resident horse or each other  4.Sit on the driveway looking out to the horizon (oh what a beautiful view?) 5. There are just so many things to do on the weekend.

This is Pebble, Miss fuzzy, OCD, loveable, our warmer in winter, loud in barks and a cutey.