Many athletes believe that physical training enhances immunity and helps prevent upper respiratory tract infection (URTI) like the common cold or \"flu\" (influenza). They also believe that physical activity and fitness help them overcome any minor infections they do get. On the other hand, based largely on anecdotes and on popularization of a link between physical or psychological stress and \"impaired immunity,\" the athletic community in general seems persuaded that intensive training, exhaustive exercise, or competition predisposes athletes to infections.