Exercise is especially important for asthmatics, according to a Denver doctor, who says more than 11 million Americans suffer from the lung disease. Asthmatics need regular aerobic exercise, ideally 30 to 40 minutes a day, three to four times a week, says Dr. Phillip Corsello, director of adult patient education and rehabilitation at the National Jewish Center for Immunology and Respiratory Medicine in Denver. "Many asthmatics experience wheezing following strenuous activity, but that doesn't mean they must sit on the sidelines and miss the physical and emotional benefits of sports and exercise," he says. He recommends swimming in a warm, indoor pool, and cautions against exercising outside on cold, windy or smoggy days.