Muscular exercise increases your body's need for glucose and oxygen. Exercise also increases the concentration of carbon dioxide in the air sacs of your lungs. A change in the concentration of carbon dioxide in your blood stimulates a series of neural and hormonal changes to increase your breathing rate and the size of your chest cavity. Such events enable your body to more quickly dispose of carbon dioxide and bring in more air and oxygen through your lungs.
Oxygen, Nutrients and Carbon Dioxide
Metabolism is the sum of all chemical reactions in your body to build up or break down tissue. Aerobic metabolism requires oxygen to convert the fat, glucose and protein from the food you eat into energy your muscle cells can use. Anaerobic metabolism does not need oxygen to convert the nutrients from the food you eat into energy your cells can use. However, the by-products of both types of metabolism are carbon dioxide and water. During muscular exercise, the rate of carbon dioxide buildup rises quickly. This stimulates your nervous, cardiovascular and respiratory systems to increase your ventilation so that the balance of gases in your blood stays within a small, healthful range necessary for your survival.
Changes in Air Pressures
Air moves from an area of high pressure to an area of low pressure. When your diaphragm or breathing muscle contracts, it moves downward from your chest cavity, which increases the space in which your lungs can expand. The air pressure in your chest cavity is less than the air pressure in your alveolar sacs. Inhalation is possible because the pressure in your alveoli is less than the pressure in the atmosphere so air flows into your lungs, filling up your alveolar sacs. Once the alveoli are filled with air, your diaphragm muscle relaxes, moving upward into the chest cavity. At this point, the pressure of the air inside your alveoli is greater than the pressure in the atmosphere, so you exhale. Muscular exercise increases the rate and force of your diaphragm contractions, increasing your ventilation.
Changes in Volume and Capacities
Your total lung capacity or the total amount of air you can inhale and exhale in one big breath is made up of four different lung volumes. Muscular exercise changes your ventilation or changes the two of the four lung volumes without changing your total lung capacity. Your inspiratory reserve volume or the amount of air you can forcibly inhale beyond a regular breath increases. Your expiratory reserve volume or the amount of air you can forcibly exhale increases beyond what you can normally exhale during a regular breath. The rate of ventilation and the volume of air you can move through your lungs increases to quickly get rid of carbon dioxide and bring in oxygen to your working muscle cells.
Considerations
Damaged lung cells from pulmonary disorders, including bronchitis and emphysema, increase the resistance in which air can flow from your mouth and nose to your alveoli. At rest, normal breathing or ventilation is sufficient to meet the body's need for oxygen use and carbon dioxide removal. However, during muscular exercise, ventilation rate must increase. People with damage to lung cells are unable to quickly move air in and out of the lungs and are therefore unable to supply the body with enough oxygen or get rid of carbon dioxide quickly. This makes it difficult to exercise because it is hard to breathe. If you have a lung condition, you must be cautious about intense muscular exercise because your lungs are simply unable to meet your body's needs.
References
- "Exercise Physiology, Energy, Nutrition & Human Performance"; William McArdle, Frank Katch and Victor Katch; 2007
- "Anatomy & Physiology"; Gary Thibodeau, Ph.D., and Kevin Patton, Ph.D.; 2007
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