新视野大学英语读写教程听力 第三册 te-unit02-a

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[00:00.00]喜欢hxen.net，就把hxen.net复制到QQ个人资料中！Iron and the Effects of Exercise
[00:-1.00]1  sports medicine experts have observed for years that endurance athletes,
[00:-2.00]particularly females, frequently have iron deficiencies.
[00:-3.00]Now a new study by a team of Purdue University researchers
[00:-4.00]suggests that even moderate exercise may lead to reduced iron in the blood of women.
[00:-5.00]2  "We found that women who were normally inactive
[00:-6.00]and then started a program of moderate exercise showed evidence of iron loss,"
[00:-7.00]says Roseanne M.Lyle, associate professor at Purdue.
[00:-8.00]Her study of 62 formerly inactive women
[00:-9.00]who began exercising three times a week for six months
[00:10.00]was published in the journal Medicine & Science in Sports & Exercise.
[00:11.00]3  "Women who consumed additional meat
[00:12.00]or took iron supplements were able to bounce back," she notes.
[00:13.00]"But the new exercisers who followed their normal diet
[00:14.00]showed a decrease in iron levels."
[00:15.00]4  Iron deficiency is very common among women in general,
[00:16.00]affecting one in four female teenagers
[00:17.00]and one in five women aged 18 to 45, respectively.
[00:18.00]But the radio is even greater among active women,
[00:19.00]affecting up to 80 percent of female endurance athletes.
[00:20.00]This means, Lyle says,
[00:21.00]that "too many women ignore the amount of iron they take in".
[00:22.00]Women of child-bearing age are at greatest risk,
[00:23.00]since their monthly bleeding is a major source of iron loss.
[00:24.00]Plus, many health-conscious women increase their risk by rejecting red meat,
[00:25.00]which contains the most easily absorbed form of iron.
[00:26.00]And because women often restrict their diet in an effort to control weight,
[00:27.00]they may not consume enough iron-rich food,
[00:28.00]and are liable to experience a deficiency.
[00:29.00]5  "The average woman takes in only two thirds
[00:30.00]of the recommended daily allowance for iron,"
[00:31.00]notes another expert.
[00:32.00]"For a woman who already has a poor iron status,
[00:33.00]any additional iron loss from exercise
[00:34.00]may be enough to tip her over the edge into a more serious deficiency,"
[00:35.00]notes the expert.
[00:36.00]6  Exercise can result in iron loss through a variety of mechanisms.
[00:37.00]Some iron is lost in sweat, and, for unknown reasons,
[00:38.00]intense endurance exercise
[00:39.00]is sometimes associated with bleeding of the digestive system.
[00:40.00]Athletes in high-impact sports such as running
[00:41.00]may also lose iron through a phenomenon
[00:42.00]where small blood vessels in the feet leak blood.
[00:43.00]7  There are three stages of iron deficiency.
[00:44.00]The first and most common is having low iron reserves,
[00:45.00]a condition that typically has no symptoms.
[00:46.00]Fatigue and poor performance may begin to
[00:47.00]appear in the second stage of deficiency,
[00:48.00]when not enough iron is present to form the molecules of blood protein
[00:49.00]that transport oxygen to the working muscles.
[00:50.00]In the third and final stage, people often feel weak,tired,
[00:51.00]and out of breath--and exercise performance is severely compromised.
[00:52.00]8  "People think that if they're not at the third stage,nothing is wrong,
[00:53.00]but that's not true,"says John L.Beard, who helped design the Purdue study.
[00:54.00]"You're not stage 3 until your iron reserves go to zero,
[00:55.00]and if you wait until that point, you're in trouble."
[00:56.00]9  However,
[00:57.00]most people with low iron reserves don't know they have a deficiency,
[00:58.00]because traditional methods of calculating the amount
[00:59.00]of iron in blood(by checking levels of the blood protein that transports oxygen)
[-1:00.00]are not sufficient,Beard states,
[-1:-1.00]Instead, it's important to check levels of a different compound,
[-1:-2.00]which indicates the amount of storage of iron in the blood.