美《纽约时报》1981年6月30日报道:加州罗马林达大学的预防医学专家伯尔克(LeeS Berk)可能已经发现常规的激烈运动有“成瘾”性质。这一发现也可以解释为什么体育运动员和芭蕾舞演员常在比赛或表演结束后才发觉受伤。伯尔克发现常规运动的人对紧张的活动产生高水平的一种天然鸦片物质叫做β-内啡肽。这种物质是脑和垂体产生的一种激素,增高对痛的耐受、抵消紧张并给予一种舒适感。β-内啡肽通常在身体应激时释出。在有6位男子和6位妇女参加的踏车试验中,那些经常缓步行走和身体健康的人比那些 The U.S. New York Times reported June 30, 1981: Preventive medicine expert LeeS Berk at the University of California at Linda may have found the “addictive” nature of conventional intense exercise. This finding may also explain why sportswomen and ballet dancers often find themselves injured after the game or show is over. Berk discovered that a normal opiate known as β-endorphin, which is produced by people who exercise regularly at high levels of nervous activity, This substance is a hormone produced by the brain and pituitary gland, increasing tolerance to pain, counteracting stress and giving a sense of comfort. Beta-endorphin is usually released when the body is stressed. In a treadmill test involving 6 men and 6 women, those who walked more often and physically than those who walked slowly