2014年12月大学英语四级写作内容储备(三)体育锻炼

　　三、 体育锻炼 (Exercise) Introduction The term is usually used in reference to any activity that

　　Introduction

　　The term is usually used in reference to any activity that promotes physical fitness. Although muscle contraction is the common element of all all forms of exercise, many other organs and systems are affected, for example, the heart and lungs. Many people also find that regular exercise enhances their sense of mental well-being along with their general physical health.

　　Today there is an increasing emphasis on preventive medicine, or maintaining health, partly as a result of the increasing costs of health care and our greater awareness of the effects of lifestyle on health and longevity. Over one-quarter of Americans (three-quarters by some standards) are significantly overweight and are at risk for a wide variety of health problems.

　　听力

　　Aerobic Exercise(有氧运动)

　　Aerobic exercise uses oxygen to keep large muscle groups moving continuously at an intensity that can be maintained for at least 20 minutes. Aerobic exercise includes walking, jogging, and swimming, and is the form recommended for reducing the risk of heart disease and increasing endurance.

　　Heart, Respiration and Exercise(体育锻炼和心脏呼吸系统的关系)

　　The heart pumps increased volumes of blood to supply oxygen and nutrients and remove carbon dioxide and metabolic wastes; the respiratory system handles an increased workload, exchanging oxygen and carbon dioxide between the blood and the atmosphere. The nervous system and various hormones have important roles as well, integrating the bodys response to exercise and regulating the metabolic changes that occur in muscle and other tissues.

　　The effects of exercise on the heart and circulation can vary considerably with intensity of exercise and with physical fitness. As a person engages in regular aerobic exercise, the heart, lungs, and muscles all become more efficient at using oxygen. The heart pumps more blood with each stroke, the lung capacity of each inhalation increases, and the muscle fibers extract more oxygen from the blood. The training effect on the heart is quite obvious when heart rates are compared between long-distance runners and sedentary individuals. The athlete will have a lower heart rate at rest (perhaps as low as 50 beats per minute) and during light jogging, for example, than the nonathlete (who might have a resting rate of 80).

　　Benefits of Exercise(体育锻炼的好处)

　　The benefits of exercise are far-reaching. Clinical and epidemiological studies have demonstrated that regular aerobic exercise reduces the risk of death due to heart disease and stroke, aids in reducing weight, helps prevent diabetes mellitus, strengthens bones, and enhances immune function. The psychological benefits are also broad, and most studies suggest a positive relationship between physical fitness and mental achievement.

　　The relationship between regular aerobic exercise and cardiovascular health and longevity is well established.

　　Many people exercise to lose weight. The number of calories burned during exercise varies greatly with the type of physical activity, but the key to successful weight reduction is to exercise regularly, without increasing food intake proportionally. One sound approach to reducing calories is to eat healthier foods that contain more fiber and less fat, and therefore fewer calories. This type of diet has also been proven healthier for the heart and blood vessels.

　　One area of controversy has been how much exercise is enough to improve general health, reduce the risk of heart disease, and increase longevity. Meaningful studies on this topic are very difficult to perform because they require large populations of subjects and many years of data collection, and because poor health sometimes results in limitations to physical activity. Despite these difficulties, it is clear that regular exercise, along with a generally healthy lifestyle, is beneficial. One recent U.S. National Institutes of Health (NIH) panel suggested that as little as 30 minutes every day of purposeful, moderately strenuous physical activity-for example, rapid walking or lawn mowing-is sufficient to lower the risk of heart disease. There is no conclusive evidence to prove that an especially rigorous exercise routine, such as running many miles per day, as opposed to walking or jogging daily, will add years to a persons life.

　　Getting in Shape(健美)

　　Physical fitness is often defined in terms of four measurements: cardiovascular-respiratory function, body composition (the proportion of lean body mass in comparison to fat), flexibility, and muscular endurance and strength. Exercise is characterized in terms of four variables as well: frequency, intensity, duration, and mode. In planning an exercise program, it is important to take into account ones personal fitness objectives and the exercise regimen that will best meet those objectives.

　　Fitness Goals(健美目标)

　　If overall fitness or prevention of heart disease is a primary goal, 20 to 30 minutes of moderate-intensity, daily aerobic exercise-such as walking, jogging, swimming, or dance aerobics-should be considered. In addition to reducing risk of heart disease, such an aerobic-exercise program will also help in weight reduction and altering body composition, and in enhancing flexibility.

　　If improving muscle strength is the primary consideration, regular, high-intensity workouts with weights are more appropriate. Studies have shown that even older people can benefit greatly from a weight-lifting workout. In particular, bone density, often a concern in the elderly, is increased by this type of exercise. A structured, supervised weight program after consultation with a physician is recommended.

　　Stretching exercises, including yoga, will enhance flexibility. In planning an exercise program, be sure to include stretching exercises and warm-up and cooldown periods to prevent muscle pulls and other injuries.

　　The most important aspect of getting in shape is to make exercise an integral part of ones lifestyle. Exercising to stay as physically fit and healthy as possible should be a lifelong commitment, and is especially important to people who perform little physical work in their day-to-day lives.