When you exercise why do you respire more?

When you exercise, your muscles work harder and need more energy, which comes from a process called cellular respiration that uses oxygen and glucose. To meet this increased demand, your breathing becomes faster and deeper to take in more oxygen and remove the extra carbon dioxide your muscles produce. At the same time, your heart pumps blood more quickly to deliver oxygen to the muscles and carry away waste, while your brain automatically signals your lungs to adjust your breathing. All of this together makes you respire more during exercise.