Exercised: Why Something We Never Evolved to Do Is Healthy and Rewarding

by Daniel E. Lieberman

and kine for “movement”), regulate inflammation. As scientists started to study when and how cytokines turn inflammation on and off, they discovered that some of the same cytokines that ignite short-lived, intense, and local inflammatory responses following an infection also stimulate lasting, barely detectable levels of inflammation throughout the body. Instead of blazing acutely in one spot for a few days or weeks, as when we fight a cold, inflammation can smolder imperceptibly in many parts of the body for months or years. In a way, chronic, low-grade inflammation is like having a never-ending cold so mild you never notice its existence. But the inflammation is nonetheless there, and mounting evidence indicates that this slow burn steadily and surreptitiously damages tissues in our arteries, muscles, liver, brain, and other organs.