why do we breathe more when we exercise

Exercise helps keep you fit and healthy by strengthening your muscles and making your heart beat faster. Your muscles, lungs, and heart all work together to move your body and make sure you are getting enough oxygen. This results in an increase in your breathing rate, or rate of ventilation. In order to reap the benefits of exercise, your heart and breathing rates must increase. Your muscles are pushing your blood back to your heart at a faster rate, so your heart must increase its rate of pumping to match. Some of the blood pumped by the heart travels to the lungs to get rid of carbon dioxide and pick up oxygen. The increase in heart rate stimulates your breathing rate. With an increase in heart rate, your blood pumps through your muscles at a faster rate, leaving less time for oxygen uptake. Having more oxygen available in the blood, from a faster breathing rate, helps the muscles get the amount they need.

Your muscles are working harder during exercise and that means their demand for oxygen increases. This happens because oxygen is needed to burn calories more efficiently. Since the blood picks up oxygen in the lungs, and the demand for oxygen increases during exercise, the lungs must work harder. With a faster breathing rate, more oxygen is picked up at the lungs for delivery to the working muscles. A by-product of metabolism is carbon dioxide. Part of the lungs function is to rid the blood of carbon dioxide. As exercise continues, or exercise intensity increases, more carbon dioxide is produced and needs to be removed. Increased breathing rate allows carbon dioxide to be expired more rapidly. Another by-product of metabolism is heat. As your body temperature rises, signals are sent to the nerves and muscles of the respiratory system to increase breathing rate.

The mechanism of this response is unknown, but increased ventilation is also often present accompanying fever. At the onset of exercise, the brain signals increases in heart and breathing rates in anticipation of the increased need for oxygen and carbon dioxide exchange of exercise. Once exercise begins, circulating levels of the hormone epinephrine also referred to as adrenaline increase. This increase stimulates ventilation as well.
When you exercise, your respiratory rate increases. This is true regardless of whether you exercise by stationary methods such as weight lifting, or by a traveling method such as jogging or biking. Clearly, an active body needs more oxygen than a body at rest. The reason for this lies in the complex chemical processes in your muscles and your bloodstream.

Your body needs oxygen at all times. Oxygen and glucose are your body s basic energy building blocks. It requires them to make your heart pump blood, to keep your lungs inhaling and exhaling, and to allow every other organ and cell to function. Every one of these activities uses up energy that must be replaced in part by taking in more oxygen. When you exercise, your muscles move more vigorously than when you are at rest. Their metabolic rate increases. They need more energy, so they produce more of the chemical energy molecule ATP. You need oxygen to produce ATP, so the more ATP you produce, the more oxygen your body requires. Oxygen reaches your muscles and other parts of the body by means of your bloodstream. Oxygen dissolves into the plasma, where most of it -- about 98. 5 percent, according to information from Eastern Kentucky University -- becomes attached to hemoglobin molecules.

While you re resting, only about 20 to 25 percent of the hemoglobin molecules give up their oxygen to your tissues. A lot of oxygen remains in the bloodstream in reserve. As you begin to exercise, you use up these reserves, and oxygen-hemoglobin saturation in your bloodstream drops sharply. You need to take in more oxygen to make up for this loss and fulfill your body s increased need for oxygen. Partial pressure of oxygen, or PO2, refers to the individual pressure exerted by oxygen in a mixture of gasses or substances. As oxygen leaves your bloodstream and enters your tissues, your bloodstream PO2 drops. At lower PO2 levels, your red blood cells make more of a substance called 2,3-diphosphoglycerate.

The increased presence of this substance helps alter the structure of your hemoglobin such that it gives up its oxygen more readily. Hemoglobin s faster release of oxygen, otherwise described as a lowered oxygen-hemoglobin saturation level, is encouraged by other conditions in an exercising body. As your muscles make extra ATP, the basic unit of energy, they also produce waste products. These are primarily carbon dioxide, or CO2, and hydrogen ions, or H+. Christian Bohr discovered in 1904 that increased concentrations of these substances encourage hemoglobin to release oxygen molecules. This principal, the Bohr effect, makes it easy for exercising muscles and other active tissues to extract the oxygen from the bloodstream in increased amounts -- but it also means you need to replenish your oxygen supplies that much more quickly.