We’re constantly being told that exercise is good for our health and can protect against a host of diseases. But a new study suggests you really can have too much of a good thing - especially if you’ve already got a weak heart.

Researchers have recognized a so-called cut-off point where exercise loses its protective effect and becomes dangerous.

Heart attack survivors who ran fewer than 30 miles a week - or walked fewer than 46 miles - were 65 per cent less likely to die from another heart-related events. But exercising too much, specifically running more than 4.4 miles a day or walking swiftly for over 6.6 miles a day, increased the risk of another heart attack.

The study, found “clear evidence” of an increase in deaths among heart attack survivors who exercise too much. In the study, the relationship between exercise and heart disease-related deaths in about 2,400 physically active heart attack survivors was examined. The study confirmed（确定）previous reports indicating that the heart-health benefits of running and walking were the same - providing（假如）people knew it takes twice as long to burn the same number of calories when walking. 

Responding to the research, Amy Thompson, Senior Cardiac Nurse at the British Heart Foundation, said: “We’re often told how beneficial physical activity is for our heart health. However, this study suggests if you’ve had a heart attack you may be putting yourself at risk of another if you participate in vigorous（剧烈的）exercise above the recommended amounts - such as running for more than 30 miles per week.”

Senior investigator Dr Alejandro Lucia, of the European University Madrid, said: “What we found on the evidence available was that best athletes, mostly men, live longer than the general population. It suggests that the beneficial health effects of exercise, particularly in reducing cardiovascular（心脑血管的）disease and cancer risk, are not necessarily limited to moderate amount.”

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1.What is mainly talked about in this passage?

A Exercise is good for one’s health.

B The more exercise you have, the healthier you are.

C Too much exercise may do harm to your heart.

D You can’t do exercise if you have a weak heart.

解析：选C。C。主旨大意题。根据文章第一段But a new study suggests you really can have too much of a good thing可知，本文将介绍一项关于运动过量将对健康有害的研究结果，故选Ｃ。

2.What is the cut-off point of healthy running every week?

A 30 miles.

B 46 miles.

C 30.8 miles.

D 46.2 miles.

解析：选A。A。细节理解题。根据文章第三段…ran fewer than 30 miles a week - or walked fewer than 46 miles - were 65 per cent less likely to die...可知，30英里是所谓的健康分界线，即每周跑步少于30英里，将会大大降低心脏病的死亡率。

3.What is the discovery of the study?

A Running and walking benefit one’s health equally.

B Walking burns the same calories with running when time doubles.

C There is an increase in death among physically active people.

D Walking does more good to those who have heart diseases.

解析：选B。B。细节理解题。根据文章第四段…it takes twice as long to burn the same number of calories when walking可知，要烧掉同样数量的热量，步行的时间是跑步的两倍。

4.What is Amy Thompson’s view about physical activity for heart health?

A Physical activity is beneficial for one’s heart health.

B Running for more than 30 miles per week is good for one’s heart health.

C Heart attack survivors should keep to the recommended amounts of exercise.

D Exercise will bring risks to people who have heart attacks.

解析：选C。C。推理判断题。根据文章第五段you may be putting yourself at risk of another if you participate in vigorous exercise above the recommended amounts可知，运动量超过推荐数量时，犯心脏病的几率将会增加，由此判断，Amy Thompson的建议是遵照推荐值，不超过分界线为好。

5.What can be inferred from the last paragraph?

A Moderate amount of exercise may not lead to the best effects.

B Men athletes live longer than women athletes in general.

C Moderate amount of exercise will prevent heart disease and cancer risks.

D Moderate amount of exercise is necessary to one’s heart health.

解析：选A。A。推理判断题。根据文章最后一段末句…the beneficial health effects of exercise… are not necessarily limited to moderate amount判断，恪守适中的运动量不一定能带来最好的效果。