What is it about walking, in particular, that makes it so amenable to thinking and writing? The answer begins with changes to our chemistry. When we go for a walk, the heart pumps faster, circulating more blood and oxygen not just to the muscles but to all the organs—including the brain. Many experiments have shown that after or during exercise, even very mild exertion, people perform better on tests of memory and attention. Walking on a regular basis also promotes new connections between brain cells, staves off the usual withering of brain tissue that comes with age, increases the volume of the hippocampus (a brain region crucial for memory), and elevates levels of molecules that both stimulate the growth of new neurons and transmit messages between them.
Perhaps the most profound relationship between walking, thinking, and writing reveals itself at the end of a stroll, back at the desk. There, it becomes apparent that writing and walking are extremely similar feats, equal parts physical and mental. When we choose a path through a city or forest, our brain must survey the surrounding environment, construct a mental map of the world, settle on a way forward, and translate that plan into a series of footsteps. Likewise, writing forces the brain to review its own landscape, plot a course through that mental terrain, and transcribe the resulting trail of thoughts by guiding the hands. Walking organizes the world around us; writing organizes our thoughts.
Walking, for me, is often a source of inspiration. And though I've never thought of writing in the same terms as walking - that is, plotting a course through mental terrain - I absolutely love (and agree with) the metaphor.
Source: Ferris Jabr, New Yorker