Aerobic exercise (also known as cardio) is a physical exercise of low to high intensity that depends primarily on the aerobic energy-generating process . The exercise stimulates the heart rate and breathing rate to increase in a way that can be sustained for the exercise session. In contrast, anaerobic (“without oxygen”) exercise is an activity that causes you to be quickly out of breath, like sprinting or lifting a heavy weight. Examples of aerobic exercises include cardio machines, spinning, running, swimming, walking, hiking, aerobics classes, dancing, cross country skiing, and kickboxing. There are many other types. It can become anaerobic exercises if performed at a level of intensity that is too high. Aerobic exercise can help prevent or reduce the chance of developing some cancers, diabetes, depression, cardiovascular disease.Imagine that you are working up a sweat, you are breathing hard, your heart is thumping, blood is coursing through your vessels to deliver oxygen to the muscles to keep you moving, and you sustain the activity for more than just a few minutes. That is an aerobic exercise, which is any activity that you can sustain for more than just a few minutes while your heart, lungs, and muscles work overtime.In this article, I’ll discuss the mechanisms of aerobic exercise: oxygen transport and consumption, the role of the heart and the muscles, the proven benefits of aerobic exercise, how much you need to do to reap the benefits, and more.The beginning of aerobic exercises. It begins with breathing. The average healthy adult inhales and exhales about 7 to 8 litres of air per minute. Once you fill your lungs, the oxygen in the air (air contains approximately 20% oxygen) is filtered through small branches of tubes (called bronchioles) until it reaches the alveoli. The alveoli are microscopic sacs where oxygen diffuses (enters) into the blood. From there, it’s a beeline direct to the heart.Reaching to the heart of it. The heart has four chambers that fill with blood and pump blood (two atria and two ventricles) and some very active coronary arteries. Because of all this action, the heart needs a fresh supply of oxygen, and as you just learned, the lungs provide it. Once the heart uses what it needs, it pumps the blood, the oxygen, and other nutrients out through the large left ventricle and through the circulatory system to all the organs, muscles, and tissues that need it.Plenty of pumping going on. Your heart beats approximately 60-80 times per minute at rest, 100,000 times a day, more than 30 million times per year, and about 2.5 billion times in a 70-year lifetime. Every beat of your heart sends a volume of blood (called stroke volume — more about that later), along with oxygen and many other life-sustaining nutrients, circulating through your body. The average healthy adult heart pumps about 5 litres of blood per minute.Consumption of oxygen and muscles. Oxygen being pumped by the blood is important. You may be familiar with the term “oxygen consumption.” In science, it’s labelled VO2 or volume of oxygen consumed. It’s the amount of oxygen the muscles extract, or consume from the blood, and it’s expressed as ml/kg/minute (millilitres per kilogram of body weight). Muscles are like engines that run on fuel (just like an automobile that runs on fuel); only our muscles use fat and carbohydrates instead of gasoline. Oxygen is a key player because, once inside the muscle, it’s used to burn fat and carbohydrate for fuel to keep our engines running. The more efficient our muscles are at consuming oxygen, the more fuel we can burn, the more fit we are, and the longer we can exercise.Health benefits of Aerobic exercise.1. DepressionMost of us who exercise regularly understand that exercise can elevate our mood. There have been a number of studies investigating the effects of exercise on depression. In one of the most recent studies, it was shown that three to five days per week for 12 weeks of biking or treadmill for approximately 30 minutes per workout reduced scores on a depression questionnaire by 47%. It’s not a substitute for therapy in a depression that causes someone to be unable to function (in which case medication and/or psychotherapy may be necessary.2. DiabetesNo study has been more conclusive about the role of lifestyle changes (diet and exercise) in preventing diabetes than the Diabetes Prevention Program according to Richard Weil. It was a study of more than 3,000 individuals at high risk for diabetes who lost 12-15 pounds and walked 150 minutes per week (five 30-minute walks per day) for three years. They reduced their risk of diabetes by 58%. That’s significant considering there are 1 million new cases of diabetes diagnosed each year. Aerobic exercise can also improve insulin resistance. Insulin resistance is a condition in which the body doesn’t use insulin properly, and this condition can occur in individuals who do and do not have diabetes. Insulin is a hormone that helps the cells in the body convert glucose (sugar) to energy.3. Cardiovascular diseaseThe list of studies that show that aerobic exercise prevents or reduces the occurrence of cardiovascular disease is so long that it would take this entire article and probably five others just like it to review all of the research. One of the most important is one of the earliest. In a study of more than 13,000 men and women, it was shown that the least fit individuals had much higher rates of cardiovascular disease than fit individuals — in some cases, the risk was twice as high. Aerobic exercise works in many ways to prevent heart disease; two of the most important are by reducing blood pressure and allowing blood vessels to be more compliant (more compliant means that they become less stiff and it’s less likely for fat to accumulate and clog up the vessels).4. Obesity and weight controlAerobic exercise is believed by many scientists to be the single best predictor of weight maintenance. You can lose weight without exercise by reducing your caloric intake enough so that you burn more calories than you consume, but it takes a regular dose of exercise to keep your weight off. The American College of Sports Medicine recommends that overweight and obese individuals progressively increase to a minimum of 150 minutes of moderate-intensity physical activity per week, but for long-term weight loss, overweight and obese adults should eventually progress to 200 to 300 minutes per week of moderate-intensity physical activity.5. Cancer preventionColon cancer: Research is clear that physically active men and women have about a 30%-40% reduction in the risk of developing colon cancer compared with inactive individuals. It appears that 30-60 minutes per day of moderate- to vigorous-intensity physical activity is needed to decrease the risk, and there is a dose-response relationship, which means that the risk declines the more active you are. Breast cancer: There is reasonably clear evidence that physically active women have a greater reduction in risk compared with inactive women.6. OsteoporosisOsteoporosis is a disease characterised by low bone density, which can lead to an increased risk of fracture. The good news is that exercise may increase bone density or at least slow the rate of decrease in both men and women. It may not work for everyone, and the precise amount and type of exercise necessary to accrue benefits are unknown, but there is evidence that it can help. In children, there is good news, too. It seems that active children have greater bone density than sedentary children.