How Much Pain for Cardiac Gain?

Since 1993, exercise guidelines promoted by the U.S. government and private organizations have held that moderate activity spread throughout the day is enough to protect against heart disease. But some researchers say that the science doesn9t support that conclusion. In their view, sustained vigorous activity--running or aerobic dancing, for example--is required. And this is no mere academic dispute, because inactivity contributes to more than a third of the nearly 500,000 heart-disease-related deaths that occur every year in the United States.