When you do strenuous exercise, you begin to take deeper breaths. Normally, when you breathe heavily, your larynx (upper airway) opens. That lets you take deeper breaths. But when you have EILO, your larynx narrows or closes altogether, making it hard to take a full breath. EILO causes shortness of breath, noisy breathing, especially when breathing in, and throat tightness. However, these feelings come on quickly and only last during exercise. They resolve right away when you stop. About 5% to 7% of people have EILO. It’s common in athletes and is more likely to affect girls than boys.