All day long, your lungs play an important role in providing oxygen for the cells throughout your body. Without the involuntary action of your lungs, you could not survive. During running, your lungs work together with your heart and circulatory system to provide oxygen to your working muscles for energy production, increasing the volume, rate and exchange of gasses to keep your legs pumping.
Breathing, also called ventilation, is a process driven by a difference in air pressure between your lungs and the atmosphere. Breathing has two phases, inspiration and expiration. During inspiration, your diaphragm and the muscles of your rib cage contract, opening up your chest cavity to provide space for your lungs to inflate. During expiration, the muscles relax, shrinking your chest cavity and pushing air back into the atmosphere. During a prolonged run, your ventilatory muscles can become fatigued, reducing your capacity to provide oxygen to your leg muscles, and causing them to fatigue as well.
The words ventilation and respiration are often used interchangeably, but they are different aspects of lung function. While ventilation is the process of breathing in and out, respiration refers to the exchange of gasses within the alveoli, which are the tiny pockets located at the end of your bronchial tree where oxygen is exchanged for carbon dioxide. As blood travels through your lungs, your red blood cells drop off carbon dioxide, a waste product of energy production, which is expelled into the atmosphere when you exhale. At the same time, O2 molecules attach to hemoglobin, a protein in your red blood cells, and are carried by the blood to your heart, to be pumped throughout your body. Respiration also takes place at the cells, where carbon dioxide is discarded and exchanged for oxygen. During running, the processes of ventilation and respiration speed up to meet oxygen demands in your leg muscles.
The tidal volume of your lungs is their capacity to inflate. Tidal volume is limited by the size of your lungs, the size of your chest cavity and the ability of your diaphragm and rib cage muscles to contract. While the size of your lungs and rib cage do not change, the strength and endurance of your inspiratory muscles can improve with training, making them more efficient at expanding your chest cavity, and more resistant to fatigue during your run.
Lung Adaptations from Running
Regular endurance training brings about improvements in your lungs' capacity to satisfy the increased oxygen demand during running. According to the Centers for Disease Control and Prevention, your maximal rate of pulmonary ventilation improves as a result of increases in both tidal volume and respiration rate. Your maximal capacity for the exchange of oxygen and carbon dioxide increases due to an increase in blood flow in your lungs, especially the upper regions. The increased flow results from a training effect that increases your blood volume, arterial diameter and the number of capillaries in your lung tissue.