Asthma is a respiratory disease that causes the lungs' airways to become inflamed and constricted, making breathing difficult. Previously, asthmatics were told not to exercise and children were often excused from gym class. One reason for this advice was the collapsed airways cause air to be trapped in the lungs. This leaves less oxygen in the blood, making physical activity much more demanding. Today, however, treatment exists which allows the asthmatic to participate at any level of any sport and in some cases emulate track-and-field medallist asthma-sufferers Jackie Joyner-Kersee and swimmer Amy Van Dyke. In 1984, 11 per cent of Olympic participants reported they suffered from exercise-induced asthma - 60 per cent of those were medal-winners. Experts now agree it is important for someone suffering from asthma to be as fit and healthy as possible. Throughout the world there has been a doubling in the number of people suffering from asthma and Hong Kong is no exception. It is estimated that five per cent of adults and as much as 11 per cent of 10-to 20-year-olds are affected in the SAR. As the number of asthmatics increases, so does the list of things known to trigger attacks. These triggers are classified as allergic, for example house dust or animals, and non-allergic, such as stress and exercise. Up to 85 per cent of asthmatics suffer from exercise-induced asthma. While the underlying causes of this condition are not fully understood, it has been described by the American College of Sports Medicine as an 'acute lung airway narrowing' that happens during and/or after physical exercise. It usually happens within the first five to 10 minutes of activity and disappears approximately one hour after stopping. Asthmatics tend to be less fit than non-sufferers. More often, people who have asthma perceive their illness as a limiting factor and therefore tend to be less physically active - yet it has been proven that exercise and fitness is vital for for them. An increase in cardiovascular fitness allows the lungs to expel air more easily so less breathing is required for a given amount of exercise. Of course, it is also critical that asthmatics work closely with their doctors in order to learn to identify individual triggers and possible medication. The type, intensity and location of activity are important for asthmatics. Studies have shown that short, easy to moderate activities, such as leisurely cycling and walking, are less likely to cause an attack than a high-intensity workouts of long duration, such as running. Research has also shown attacks tend to happen more often after running than cycling or swimming. Finally, hydration is even more important for asthmatics in order to help decrease airway restriction. A carefully controlled exercise programme can improve the fitness and health of people who suffer from asthma, even exercise-induced asthma. With preventative strategies to help avoid attacks as well as medication, the asthmatic can participate in any form of exercise safely.