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

by Daniel E. Lieberman

The heart is essentially a muscular pump connected to an elaborate network of branching tubes. Although there are several kinds of cardiovascular disease, almost all arise from something going wrong in either the tubes or the pump. Most problems start with the tubes, primarily the arteries that carry blood from the heart to every nook and cranny of the body. Like the pipes in a building, arteries are vulnerable to getting clogged with unwanted deposits. This hardening of the arteries, termed atherosclerosis, starts with the buildup of plaque—a gloppy mixture of fat, cholesterol, and calcium—within the walls of arteries. Plaques, however, don’t simply accumulate in arteries like crud settling in a pipe. Instead, they are dynamic, changing, growing, shifting, and sometimes breaking. They develop when white blood cells in arteries trigger inflammation by reacting to damage usually caused by a combination of high blood pressure and so-called bad cholesterol that irritates the walls of the artery. In an effort to repair the damage, white blood cells produce a foamy mixture that incorporates cholesterol and other stuff and then hardens. As plaque accumulates, arteries stiffen and narrow, sometimes preventing enough blood from flowing to the tissues and organs that need it and further driving up blood pressure. One potentially lethal scenario is when plaques