Exercise-induced bronchospasm--or sports asthma--is thought to be caused by the intense breathing during exercise that results in evaporative water loss from the lungs. This loss of water vapor cools the breathing tubes, provoking bronchospasm and thus asthmatic symptoms.
In fact, EIB or sports asthma is most common when exercising during the winter when the air is cold and dry, which enhances the cooling of the airways. However, the degree of EIB or sports asthma also can worsen during the allergy season when you are exposed to pollen.
Symptoms often last a short time and may resolve without treatment simply by resting. On the other hand, untreated symptoms occasionally may evolve into a serious asthmatic attack requiring emergency treatment or even hospitalization. Following each episode of sports asthma, a refractory (symptom-free) period begins within 30 minutes and can last 90 minutes where little or no bronchospasm can be induced even if rechallenged with vigorous exercise. Athletes often take advantage of this fact by warming up vigorously in order to induce a refractory period prior to competition. You may also have a second phase of symptoms occurring some hours after the initial symptoms have appeared to resolve. This is often referred to as a "late-phase reaction."
Most children and adults with EIB or sports asthma can participate in most sports and exercise with proper treatment. However, a small percentage of asthmatic sufferers may still have some trouble when they exercise vigorously even with a comprehensive treatment program. These individuals would do better to select sports that are less likely to provoke asthma. Sports that require a high level of running with little time for breaks and vigorous continuous activity (long-distance running, soccer, basketball) are more likely to cause symptoms than sports such as baseball or tennis that allow rest periods. Swimming, which takes place in warm, humid air, is often the best type of exercise for individuals with EIB or sports asthma.