For me it is anything that helps me not fix on the problem. Standing in front of the computer, staring at the code always pushes me in the same direction; once I am up to something else, but still 'lightly' thinking about the problem I come up with better solutions. It's almost as if I am thinking about it I can't think of anything valuable; once I stop thinking about the issue at hand everything just happens to fall in place.
For solving problems showers are faster, but walking is better for higher level problems requiring greater thought. A shower is great for knocking out a block quickly, while if I have a really hard problem a long walk is better.
I wonder if there's a patent on a treadmill shower desk.
Now just add a fridge and a microwave and you'll almost never have to get off.