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 body's 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 person's 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 one's 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 one's 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.
四、人类疾病(Human Disease)
Human Disease, in medicine, any harmful change that interferes with the normal appearance, structure, or function of the body or any of its parts. Since time immemorial, disease has played a role in the history of societies. It has affected—and been affected by—economic conditions, wars, and natural disasters. Indeed, the impact of disease can be far greater than better-known calamities. An epidemic of influenza that swept the globe in 1918 killed between 20 million and 40 million people.
Diseases have diverse causes, which can be classified into two broad groups: infectious and noninfectious. Infectious diseases can spread from one person to another and are caused by microscopic organisms that invade the body. Noninfectious diseases are not communicated from person to person and do not have, or are not known to involve, infectious agents. Some diseases, such as the common cold, are acute, coming on suddenly and lasting for no more than a few weeks. Other diseases, such as arthritis(关节炎), are chronic, persisting for months or years, or recurring frequently.
Every disease has certain characteristic effects on the body. Some of these effects, called symptoms and signs, include fever, inflammation(发炎), pain, fatigue(疲劳), dizziness(头晕), nausea(恶心), and rashes(皮疹), and are readily apparent to the patient. These symptoms offer important clues that help physicians and other health care professionals make a diagnosis(诊断). Many times, however, the symptoms point to several possible disorders. In those cases, doctors rely on medical tests, such as blood examinations and X rays, to confirm the diagnosis.
The course of a disease—that is, the path it follows from onset to end—can vary tremendously, depending largely on the individual and the treatment he or she receives. For example, otherwise healthy people usually recover quickly from a bout of pneumonia if given proper treatment, whereas pneumonia often proves fatal to people with a weakened immune system and to those who do not receive prompt, effective treatment.
Preventing the Diseases(疾病预防)
It is much less costly, in terms of both human suffering and economics, to prevent disease than to treat it. Public health services and medical professionals play critical roles in helping people avoid disease. In addition, each individual plays a vital role in protecting his or her personal health.
Public health services are charged with protecting community health. Their activities include provision of adequate clean water and the sanitary disposal of sewage and other wastes.
Physicians, dentists, and other medical experts have a number of preventive tools at their disposal. Among the most effective are vaccines(注射疫苗), which stimulate the immune system to produce antibodies against particular antigens.
Regular medical check-ups are another important preventive tool. These help doctors to find disease in its early stages, when it is easier to treat and before it causes significant damage.
Even the finest public health and medical services are of limited value to people who have poor health habits. Numerous studies have proven that physical health and longevity are linked to the following: eating a balanced diet, maintaining proper weight, exercising regularly, avoiding tobacco, and avoiding alcohol or consuming it in moderation. People who fail to follow these guidelines increase their risk of cardiovascular disease, cancer, hepatitis(肝炎), and other lethal diseases(致命疾病).
Life Span(寿命)
At the beginning of the 20th century, people in the United States had an average life span of about 50 years. By the time the century neared its close, average life span had risen to 76 years. Other developed countries experienced similar increases. Much of the credit for these longer life spans—and for the good health that accompanies them—is due to the conquering of diseases, thanks to vaccines, antibiotics, sophisticated surgical tools, and other medical miracles. The challenges ahead include bringing the benefits of this medical knowledge to all peoples of the world, and expanding on current knowledge in order to understand, treat, and prevent the diseases that still confront us.
Influenza(流感)
Influenza is an acute disease with a rapid onset and pronounced symptoms. After the influenza virus invades a person’s body, an incubation period of one to two days passes before symptoms appear. Classic symptoms include sore throat, dry cough, stuffed or runny nose, chills, fever with temperatures as high as 39º C (103º F), aching muscles and joints, headache, loss of appetite, occasional nausea and vomiting, and fatigue. For most people flu symptoms begin to subside after two to three days and disappear in seven to ten days. However, coughing and fatigue may persist for two or more weeks.
Breathing Problems(呼吸疾病), diseases or conditions affecting respiration, usually caused by cigarette smoke or other pollutants, allergies, or an inherited trait.
Diarrhea(腹泻), frequent passage of abnormally loose, watery stool. Diarrhea usually develops suddenly and may last from several hours to a few days. It is often accompanied by abdominal pains, low fever, nausea, and vomiting. Diarrhea is not a disease. It is a symptom of numerous disorders, such as food poisoning from contaminated foods or beverages, infections by viruses and bacteria, or anxiety. The usual treatment for diarrhea consists of bed rest, drinking liquids to replace fluids and salts lost from the body, and eating soft foods.
Severe mental illness (精神疾病)almost always alters a person’s life dramatically. People with severe mental illnesses experience disturbing symptoms that can make it difficult to hold a job, go to school, relate to others, or cope with ordinary life demands. Some individuals require hospitalization because they become unable to care for themselves or because they are at risk of committing suicide.
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