Your body uses oxygen to produce energy. Oxygen cannot be stored in the body and muse be continually inspired. Therefore as your body expends more energy you must respire more. Your breathing rate is controlled by several factors including cellular oxygen utilization, carbon dioxide production and natural control mechanisms. All these factors come into play when you exercise, leading to breathing changes.
Increased Ventilation with Exercise
When you begin to exercise the volume of gas you expire per minute increases linearly as does the amount of oxygen you inspire. This holds true until you reach 60 percent of your maximum work capacity. Above that work level these lines begin to curve. As you work harder your body accumulates lactic acid. This is counterbalanced by an increase in carbon dioxide which stimulates respiration.
Constant Exercise
Your response to a constant level of exercise has several stages. In the first stage there is an immediate rapid increase in respiration. This increase slows but continues as you continue to exercise. However your respiration will eventually reach a level where it can remove the extra carbon dioxide and provide you with enough oxygen. At this point your respiratory rate will stay steady at a level that is increased above your normal respiratory rate when you are not exercising.
Carotid Bodies
The carotid bodies are a cluster of chemical sensors located near the carotid arteries. During exercise they sense changes in the gas components of your blood including increases in carbon dioxide. They then signal your body to increase respiration.
The Medulla
The medulla is the part of the brain that controls respiratory rate. The medulla responds to changes in carbon dioxide, not oxygen. During exercise the medulla senses the increased carbon dioxide levels in your blood and signals your lungs to breathe faster.
