tailieunhanh - Trắc nghiệm tổng hợp trình độ C

Hãy đọc kỹ các câu sau và chọn đáp án đúng với những lựa chọn cho sẵn. Bài tập này được trích ra từ những đề thi chứng chỉ quốc gia trình độ C. | A preventive medicine specialist may have found the reason for the "addictive" properties of regular exercise. The finding may also explain why athletes often fail to notice an injury until after the competition is over. Dr. Lee S. Berk has found that persons who exercise regularly produce high levels of a natural opiate called beta-endorphin in response to strenuous activity. This substance, a hormone produced by brain and the pituitary gland, increases pain tolerance, counters stress, and imparts a feeling of well-being. In his study of six men and six women who were tested on a treadmill, those who jogged regularly and were physically fit produced beta-endprphin more rapidly and in far greater amounts than those who were usually sedentary. After the activity was stopped, beta-endorphin vevels drops back to normal. In the nonrunners, only a small rise in beta-endorphin occured while they exercised. However, a larger increase in beta-endorphin production was noted some time after the activity was finished, when it was ineffective. noted that beta-endorphin production may also account for other benefits of vigorous exercise, sich as its ability to lower blood pressure and suppress appetite, both of which are known effects of the hormone. "Beta-endorphin may also explain why people become addicted to exercise," Dr. Berk said.