Question

    Athletes who can run several marathons in just months might seem unstoppable.The biggest obstacle，it turns out，is their own bodies.A new study find out for the first time a “ceiling” for endurance activities such as long­distance running and biking.

“Physiologists and athletes alike have long been interested in just how far the human body can push itself.When exercising over a few hours，a wealth of evidence suggests most people max out at about five times their basal metabolic(代谢的)rate(BMR)．How humans use energy during longer endurance activities is another question entirely，”says Herman Pontzer，an evolutionary theorist at Duke University，North Carolina.

Pontzer saw an opportunity to answer that question when Bryce Carlson，an endurance athlete and former biochemist at Purdue University，organized the Race Across the USA in 2015.Runners covered 4，957 kilometers over the course of 20 weeks in a series of marathons stretching from Los Angeles，California，to Washington，D.C.

To find out how many calories the athletes in the study burned，Pontzer，Carlson，and colleagues replaced the normal hydrogen and oxygen in their drinking water with harmless，uncommon isotopes(同位素)of those elements.By chemically tracing how these isotopes flush out in urine，sweat，and breath，scientists can calculate how much carbon dioxide an athlete produces — a measure that directly relates to how many calories they burn.

Pontzer's team then collected energy consumption data over the course of the race to see how many calories they burned per day.They found that whatever the event is，energy consumption leveled off after about 20 days，eventually staying at a steady level at about 2.5 times an athlete's BMR.At that point，the body is burning calories more quickly than it can absorb food and turn it into energy，representing a biologically determined ceiling on human performance.

“It was just one of those moments of discovery that as a scientist you just live for，” Pontzer said.“We ended up plotting out the very limits of human endurance，the envelope for what humans can do.”

1.What does the underlined word “ceiling” in the first paragraph refer to?

A.The weakness of human bodies.

B.The effect of lasting exercise.

C.The way humans use energy.

D.The limit of human endurance.

2.Which of the following is a direct measure of an athlete's energy consumption?

A.The hydrogen and oxygen in their drinking water.

B.The carbon dioxide their bodies create.

C.The amount of their urine，sweat and breath.

D.The remaining isotopes in their body.

3.What is the purpose of Pontzer's study?

A.To confirm that an athlete's physical extreme is mainly determined by his BMR.

B.To compare human limits in common exercise with those in endurance activities.

C.To find out where the highest energy consumption of an athlete lies.

D.To set a reasonable standard for researches concerned with human body

4.How did Pontzer feel when their study results came out?

A.Excited. B.Regretful.

C.Surprised. D.Hopeful.

Answer

1.D

2.B

3.C

4.A

【解析】

这是一篇说明文。文章主要介绍了人类耐力活动的极限。

1.词义猜测题。阅读全文可知本文主要讲述了人类运动的耐力活动的极限，再根据划线词的所在句子A new study find out for the first time a “ceiling” for endurance activities such as long­distance running and biking.一项新的研究首次发现了长距离跑步和骑自行车等耐力活动的_______，因此可以推断出ceiling的意思为“极限”。故选D项。

2.细节理解题。根据第四段最后一句By chemically tracing how these isotopes flush out in urine, sweat, and breath, scientists can calculate how much carbon dioxide an athlete produces—a measure that directly relates to how many calories they burn.可知，通过化学追踪这些同位素是如何在尿液、汗液和呼吸中排出的，科学家们可以计算出一名运动员产生了多少二氧化碳——这一指标直接关系到他们燃烧了多少卡路里。故选B项。

3.细节理解题。根据第四段To find out how many calories the athletes in the study burned，Pontzer，Carlson，and colleagues replaced the normal hydrogen and oxygen in their drinking water with harmless，uncommon isotopes(同位素)of those elements. By chemically tracing how these isotopes flush out in urine，sweat，and breath，scientists can calculate how much carbon dioxide an athlete produces — a measure that directly relates to how many calories they burn. 为了找出参与研究的运动员燃烧了多少卡路里，庞泽，卡尔森和同事们用无害的、不常见的同位素来代替饮用水中的正常的氢和氧。通过化学追踪这些同位素是如何从尿液、汗水和呼吸中排出的，科学家们可以计算出一名运动员产生了多少二氧化碳。可知，庞泽的团队研究的目的是找出参与研究的运动员的能量消耗有多少，在什么方面消耗。故选C项。

4.推理判断题。根据最后一段“It was just one of those moments of discovery that as a scientist you just live for，” Pontzer said.“We ended up plotting out the very limits of human endurance，the envelope for what humans can do.”“作为一名科学家，这只是发现的其中一个时刻，”庞泽说，“我们最终画出了人类耐力的极限，人类所能做的极限。”可知，庞泽发现了他想要的结果，肯定是很兴奋的。故选A项。