Your respiratory system controls your breathing and begins when you draw in air through your nose or mouth. The air travels through your windpipe into both of your lungs, where small air sacs capture oxygen and distribute it in your bloodstream through small blood vessels called capillaries. Your diaphragm is the muscle the controls respiration and contracts when you inhale. Your diaphragm then relaxes, collapses your chest and forces out carbon dioxide when you exhale.
Capillaries surround small air sacs, called alveoli, inside your lungs that capture the oxygen you breathe in. Your lungs adapt to regular exercise by activating more alveoli. More alveoli can supply more oxygen to working muscles and tissues throughout your body. Pneumonia occurs when fluids in your lung prevent alveoli from exchanging gases. Having more alveoli can suppress the effects of pneumonia by reducing the proportion of alveoli that are affected by this disease. Emphysema occurs when alveolar walls break down and gradually reduce the exchange of oxygen and carbon dioxide in your lungs. Regular exercises may help slow the progression of emphysema by increasing the number of gas-exchanging alveoli.
Exercise exposes your lungs to stronger rushes of airflow. Aerobic exercise in particular exposes your lungs to strong and constant rushes of air. This activity helps clear mucus in your lungs. Mucus build-up can diminish your lung capacity and lead to bacterial infections. According to a 1997 "European Respiratory Journal" article by the University of Ulsan's Wong Don Kim, excessive mucus in your lungs is associated with higher mortality, may obstruct airflow and increases your risk of infections. Regular exercise can help offset these conditions by preventing mucus from building up in your lungs.
Capillaries are the smallest blood vessels in your body. Oxygen seeps out of thin capillary walls as carbon dioxide seeps in during respiration. Exercise stimulates vasodilation, which increases the diameter of blood vessels in your body, including the capillaries. Your body adapts to long-term exercise by increasing the size and number of capillaries, including alveolar capillaries. This adaptation makes the exchange of carbon dioxide and oxygen more efficient.
The skeletal muscles that control respiration include your diaphragm and intercostals. Your diaphragm is a broad band of muscle that sits under your lungs and forms the base of a region known as the thoracic cavity by attaching to the lower parts of your ribs, sternum and spine. The intercostals form the muscle tissue in between individual ribs. The long-term effect of exercise is to build the endurance of these respiratory muscles, allowing deeper, fuller and more efficient breaths.