Introduction
The process of breathing allows oxygen to enter the bloodstream to fuel most every tissue, system and structure in the human body. Muscles are tissue that benefit from this oxygen. Because the body doesn't have the ability to store oxygen, the lungs must continually inhale oxygen to supply the blood with the oxygen needed to live. As your body needs more oxygen, it adjusts the amount through a process called your respiration rate. Your respiration rate is how many breaths (one inhale and one exhale) you take in one minute.
Medulla
Your breathing rate is controlled by a structure in the brain called the medulla. Within the medulla are groups of neurons that control your respiration rate. Depending on what activity you take part in and how taxing it is on your body, your medulla senses the oxygen needs for that activity and adjust the respiration rate as needed.
Oxygen
When you exercise, your body needs a greater amount of oxygen to keep up with the increase in activity. An exercising muscle burns oxygen at a much faster rate than a muscle that's at rest. Because the muscles need oxygen to operate and to heal, as you exercise your muscles require more oxygen than your lungs can provide at a resting rate. The medulla has to increase your breathing rate to prevent your body from collapsing.
Carbon Dioxide
As your muscles work, they use oxygen at a greater rate and produce waste products as a result of the energy-creation process in the cells. One of these waste products is carbon dioxide. The cells of the muscles get rid of this waste product by putting it back into the bloodstream in the veins. As the levels of carbon dioxide increase in the bloodstream, the body transmits a warning signal to the medulla. The medulla reacts by sending a signal to the lungs and the heart. This causes the lungs to breathe faster and in a deeper volume. It also causes the heart to beat at an increased rate to pull the oxygen to the muscles faster, and remove the carbon dioxide faster to be exhaled. This keeps the bloodstream balanced, and provides the muscles with needed oxygen while you exercise.
