From weekend warriors to superstars, all types of athletes experience exercise-induced asthma. They include world-class competitors like NFL star Jerome "The Bus" Bettis and six-time Olympic gold medalist swimmer Amy Van Dyken.
But just what is exercise-induced asthma, why does it happen, and how can it be managed?
WebMD consulted the experts to find out the answers to these questions, as well as tips for controlling symptoms of exercise-induced asthma -- whether you're a casual athlete or a superstar.
What is Exercise-Induced Asthma?
Even many people who never experience asthma symptoms at other times have exercise-induced asthma, experts say.
"Exercise-induced asthma occurs in almost everyone who has chronic asthma, but there is a separate group of people who have what we call exercise-induced bronchospasm," says Timothy J. Craig, MD, chair of the American Academy of Allergy, Asthma and Immunology's Sports Medicine Committee.
These people, explains Craig, don't have what is considered "true" asthma. They don't have inflammation in their lungs. Nor do they experience symptoms when exposed to common triggers, like animals, pollen or mold.
"So unlike most people who have asthma and get exercise-induced symptoms, these individuals don't have true asthma, but when they exercise, they experience the symptoms of asthma," Craig tells WebMD.
Exercise-induced asthma, experienced by up to 13% of the U.S. population, occurs when the airways narrow, making breathing difficult. Why some athletes have exercise-induced asthma and others don't isn't entirely clear.
"The causes vary, but are usually associated with loss of heat or water, or both, from the lungs during exercise, because of the increased ventilation of dry and cool air," says Michael G. Miller, EdD, a spokesperson for the National Athletic Trainers Association.
People with exercise-induced asthma have airways that are overly sensitive to sudden changes in temperature and humidity, especially when breathing colder, drier air, according to the American Academy of Allergy, Asthma and Immunology (AAAAI).
During strenuous activity, people tend to breathe through their mouths. Mouth breathing allows cold, dry air directly into the lungs, without benefit of the warmth and moisture that nose breathing supplies. As a result, air is moistened to only 60-70% relative humidity. Nose-breathing, meanwhile, warms and saturates air to about 80 to 90% humidity.
The symptoms of exercise-induced asthma are similar to those of chronic asthma, explains Miller. They include: