The repetitive footfalls and arm swinging can lull walkers into a dreamlike state.
Some psychotherapists actually walk with their patients to take advantage of the calming effect.
And I suspect it could happen in less time than that. Like any aerobic activity, walking heats up your body, thus reducing muscle tension. Researchers also believe this type of exercise increases the level of certain chemicals in your brain, triggering a relaxation message. When a problem nags at the back of your mind, take a walk. According to yet another theory, during exercise the brain relies more on the creative right side and less on the rigid left side.