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.
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.
Veins have thinner, less elastic walls than arteries. Also, veins contain small valves to prevent the backward flow of blood to the heart. The veins are intertwined in the muscle; therefore, when the muscle is contracted the vein is squeezed, pushing the blood on its way back to the heart. A malfunction of the valves results in a failure to remove used blood at the proper rate. As a result, venous blood pools, especially in the legs, causing a condition known as varicose veins.
Good cardiovascular fitness requires a fit respiratory system and fit blood. The process of taking in oxygen (through the mouth and nose) and delivering it to the lungs, where the blood picks it up, is called external respiration. External respiration requires fit lungs as well as blood with adequate hemoglobin in the red blood cells. Insufficient oxygen-carrying capacity of the blood is called anemia.
Delivering oxygen to the tissues from the blood is called internal respiration. Internal respiration requires an adequate number of healthy capillaries. In addition to delivering oxygen to the tissues, these systems remove CO2. Good vascular fitness requires fitness of both the external and internal respiratory systems.
Cardiovascular fitness requires fit muscle tissue capable of using oxygen. Once the oxygen is delivered, the muscle tissues must be able to use oxygen to sustain physical performance. Cardiovascular fitness activities rely mostly on slow-twitch muscle fibers. These fibers, when trained, undergo changes that make them especially able to use oxygen. Outstanding distance runners often have high numbers of slow-twitch fibers and sprinters often have high numbers of fast-twitch fibers.
Regular physical activity reduces the risk of heart disease. There is considerable evidence that regular physical reduces the incidence of heart disease. Also, it reduces the chances of early death from heart disease. In fact, the benefits of exercise in preventing heart disease have been shown to be independent of other risk factors. Inactivity is now considered a primary risk factor for heart disease.
People with low cardiovascular fitness have increase risk of heart disease. The best evidence indicates that cardiovascular fitness is associated with heart disease. Research has shown that low fit people are especially at risk. In addition it has now been demonstrated that improving your fitness (moving from low fitness to the good fitness zone) has a positive effect on health.
The frequency, intensity and time of your physical activity will vary depending on the benefits you hope to achieve. The term “threshold of training” suggests that there is one level of physical activity that all people must do to achieve cardiovascular fitness as well as the health benefits of activity. We now know that the threshold differs for people depending on their current fitness and activity levels and the benefits they hope to achieve. New studies show that health benefits can be achieved by doing less activity than previously thought. However, those who desire “performance benefits” as indicated by a high level cardiovascular fitness, in addition to the health benefits of physical activity, will need to do activity at a higher threshold level than those who are interested primarily in the basic health benefits.
The type of physical activity you select is important to the benefits you will receive. Lifestyle physical activities, such as walking, yard work, climbing stairs and normal daily tasks, can promote health benefits and make contributions to your cardiovascular fitness. Aerobic activities such as running, skiing, cycling, and active sports are considered to be the most beneficial in promoting health benefits and are effective in promoting performance increases needed for high-level performance. Though sports can be effective in contributing to the development of cardiovascular fitness, some are relatively ineffective and others can be very effective.
As a minimum, adults should participate in regular physical activity equal to 30 minutes of brisk walking most, preferably all, days of the week. Research shows that 30 minutes of physical activity equal to brisk walking most days of the week is an important contributor to personal cardiovascular health. To achieve health benefits, physical activity can be accumulated in several 10 to 15 minute bouts that total 30 minutes daily. However, when possible, bouts of 30 minutes duration are recommended. Near daily activity is recommended because each activity session actually has short-term benefits, which do not occur if activity is not relatively frequent. This is sometimes referred to as the “last bout effect”.
Calories can be counted to determine if you are doing enough to receive cardiovascular benefits of physical activity. The threshold of training for producing many of the health benefits can be determines using a weekly calorie count. Scientific evidence suggests that people who regularly expend calories each week in lifestyle activities such as walking, stair climbing and sports reduce death rates considerably compared to those who do not exercise. As few as 500 to 1,000 calories expended in exercise per week can reduce death rate, but most experts suggest that to insure a health benefit no less than 1.35 calories per pound of body weight each day. This amounts to 1,000 to 2,000 calories per week for most people if exercise is done daily.
For optimal health benefits an expenditure of 2,000 to 3,500 calories per week is recommended, because people doing this much physical activity have 48 to 64 percent less risk of heart disease when compared to sedentary people. As the calories expended per week increase the death rate decreases proportionately up to 3,500 calories. Because additional benefits do not occur for those expending more than 3,500 calories per week, the target zone is 1,000 to 3,500 calories per week. For health benefits to occur, calories must be expended on most days of the week and over long periods of time. In other words, moderate physical activity is described here must become regular lifetime physical activity if optimal health benefits are to be obtained. It should also be pointed out that some vigorous sports participation as part of the calories expended each week enhances the benefits of moderate regular calorie expenditure.