Denver is one of 10 cities across the country taking part in a study to see whether exercise helps stimulant abusers kick the habit.  The study will also compare those in the exercise group to other abusers who will receive health counseling instead of exercise. The study is being led by the National Institute on Drug Abuse.  Participants in the Denver trial will all be in treatment at Arapahoe House, a network of 14 locations in the Denver metro area that treat drug and alcohol abusers. Joining us is Meredith Silverstein, who directs the research branch of Arapahoe House.