Your breathing increases in direct proportion to the intensity of your workout. That happens because the oxygen you inhale has the simple job of carrying away the chemical fragments your body makes when you burn sugar for energy. Those fragments are hydrogen atoms which your body combines with oxygen to make water, and carbon atoms which your body combines with oxygen to make carbon dioxide.
Ventilation, as it relates to the human body, has only one very specific definition--carbon dioxide, CO2, elimination. The terms ventilation and hyper-ventilation are often mistakenly used as synonyms for breathing. For example, if you breathe very fast but shallow, you will move exhaled air from your lungs only as far as your trachea, commonly called your wind-pipe, before you inhale again. That might look like a lot of breathing but hardly any stale air is moved out and very little fresh air comes in. That fast breathing pattern is only hypo-ventilation, under-ventilation, because it never expels enough carbon dioxide. Only normal or deep breathing produces ventilation.
Your alveoli are delicate microscopic bubbles that fill your lungs, connected to airways that carry air in and out of them. They are extremely thin sacks of tissue holding a network of capillaries, or minute blood vessels. If you could spread all your alveoli onto a flat surface they would cover an area about as big as a tennis court. That exposes all of your blood, one single red blood cell at a time, to the fresh air you fill your lungs with on every deep breath. Perfusion, or blood flow, must match ventilation so oxygen diffuses into your blood and CO2 diffuses out properly. You cannot ventilate properly without healthy alveoli.
Exercise makes carbon dioxide by oxidizing, or burning, sugar molecules. Every time your muscles break up a sugar molecule into carbon and hydrogen fragments electrons are set loose to activate your muscle and nerve fibers. Without their electrons, the carbon and hydrogen atoms need something else to grab onto. That is oxygen's job and the reason your muscles and nerves need it when you exercise. Exercising muscles make energy and CO2. The more CO2 you make, the more you have to ventilate your alveoli to get rid of it. Exercise increases your alveolar ventilation.
Carbon Dioxide Sensitivity
Your brain and certain receptors in your blood vessels are exquisitely sensitive to CO2 in your blood. If your CO2 goes up even one or two percent during exercise, your brain will command a doubling or more in your breathing rate and volume. You notice this as a sudden onset of shortness of breath--your brain's signal for you to increase alveolar ventilation to match your exercise.