imagine that you're exercising. you're working up a sweat you're 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's aerobic exercise; any activity that you can sustain for more than just a few minutes while your heart lungs and muscles work overtime. the beginning it all starts with breathing. the average healthy adult inhales and exhales about 7 to 8 liters 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 tiny sacs (they kind of look like bunches of grapes and you have about 300 000 000 in each lung! ) where oxygen diffuses (enters) into the blood. from there it's a beeline direct to the heart. getting 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 large and 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 tissue that need it. a whole lot 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 along with oxygen and many other life-sustaining nutrients circulating through your body. the average healthy adult heart pumps about 5 liters of blood per minute. oxygen consumption and muscles all that oxygen being pumped by the blood is important. you may be familiar with the term "oxygen consumption. " in science it's labeled vo 2 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 (milliliters 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 carbohydrates 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.
what is aerobic exercise?