四级写作常见话题及范文：体育锻炼

　　Introduction

　　The term is usually used in reference to any activity that promotes physical fitness. Although muscle contraction is the common element of 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.

　　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.