Hi. I had gone through your question and understand your concerns. As I understand, your son is having asthma for long time. Exercise or exertions are known triggers of asthma symptoms in those who ave chronic asthma. And in some people exercise may be the only trigger for asthma symptoms. When asthmatic patients exercise, they inhale cold, dry air through the mouth; this causes sensitive airways of these people to spasm leading to breathing difficulty, cough, chest tightness and wheezing. This happens particularly when it s too cold, during pollen season and when air is polluted. When you give salbutamol (Ventolin) inhaler, it opens up the contracted airways and symptoms improve. One way to avoid this is use of salbutamol inhaler before doing the exercise. And if it happens regularly, daily use of preventive medicines like steroid inhalers or montelukast tablet is advisable. Hope I have answered your queries. Thanks for using Healthcare Magic.