Being able to work more effectively and think more clearly are effects that occur mainly after physical exertion. But even while running, you can often notice what movement does to your brain. Think, for example, of the enlightening insights you come home with after a run. This has to do with the way the left and right hemispheres of your brain work together. The left hemisphere is responsible for logic, analytical skills and the ability to understand. The right hemisphere is the creative part of your brain and is used, among other things, to see connections.
During your working day, the left hemisphere of the brain is under particular strain. Exercise makes the right hemisphere of the brain more active and both hemispheres work better together. When the right hemisphere of the brain is stimulated, you act more intuitively and think more creatively. That explains why you suddenly get good ideas and innovative insights while running. A bit of running during your lunch break will get you back to work with a fresh mind.