How does a turtle get exercise?

I have two yellow bellied sliders that are around an inch and a half long. They get their daily exercise by swimming around the tank, but it isn't very deep so every day or every other day I put them in a tub with 6 inches of water so they can stay healthy and not get overweight. But don't overwork them! Watch them the whole time they're in there and take them out after 15-30 minutes or when they are tired and return them to the cage. But to answer your question, they basically SWIM!!