By 2030, census data suggests, 20-plus percent of the U.S. population will be 65 or older. Many aging baby boomers who need a cheap place to exercise need look no further than the nearby mall. 

Mall walking's popularity has grown such that the Centers for Disease Control and Prevention recently published its first manual to encourage retail managers to offer programs that get community residents moving. Basia Belza, a University of Washington professor of nursing, was a corresponding author on the guide.