Cardiovascular fitness is sometimes referred to as "cardiovascular endurance" because a person who possesses this type of fitness can persist in physical exercise for long periods of time without undue fatigue. It has been referred to as "cardio-respiratory fitness" because it requires delivery and utilization of oxygen, which is only possible if the circulatory and respiratory systems are capable of these functions.
The term "aerobic fitness" has also been used as a synonym for cardiovascular fitness because "aerobic capacity" is considered to be the best indicator of cardiovascular fitness and aerobic physical activity or exercise is the preferred method for achieving it. Regardless of the words used to describe it, cardiovascular fitness is complex because it requires fitness of several body systems.
Good cardiovascular fitness requires a fit heart muscle. The heart is a muscle; to become stronger it must be exercised like any other muscle in the body. If the heart is exercised regularly, its strength increases; if not, it becomes weaker. Contrary to the belief that strenuous work harms the heart, research has found no evidence that regular progressive exercise is bad for the normal heart. In fact, the heart muscle will increase in size and power when called upon to extend itself. The increase in size and power allows the heart to pump a greater volume of blood with fewer strokes per minute. The average individual has a resting heart rate of between seventy (70) and eighty (80) beats per minute, whereas it is not uncommon for a trained athlete's pulse to be in the low fifties or even in the forties.millerfit.com
The healthy heart is efficient in the work it does. It can convert about half of its fuel into energy. An automobile engine in good running condition converts about one-fourth of its fuel into energy. By comparison, the heart is an efficient engine. The heart of a normal individual beats reflexively about 40 million times a year. During this time, over 4,000 gallons, or 10 tons, of blood are circulated each day, and every night the heart's workload is equivalent to a person carrying a thirty-pound pack to the top of the 102-story Empire State Building.
Good cardiovascular fitness requires a fit vascular system. Healthy arteries are elastic, free of obstruction and expand to permit the flow of blood. Muscle layers line the arteries and control the size of the arterial opening upon the impulse from nerve fibers. Unfit arteries may have a reduced internal diameter because of deposits on the anterior of their walls, or they may have hardened, nonelastic walls.
Fit coronary arteries are especially important to good health. The blood in the four chambers of the heart does not directly nourish the heart. Rather, numerous small arteries within the heart muscle provide for coronary circulation. Poor coronary circulation precipitated by unhealthy arteries can be the cause of a heart attack.
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