人体的十二个极限

iavjssssmqee · 发表于 2010-5-4 18:43:38

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THE ASTOUNDING LIMITS OF ENDURANCE

We have an irrepressible urge to push our boundaries and set records. How much further can we go, physically and mentally, before we reach our ultimate limits?
1 What's the human speed limit?

Last year, Usain Bolt stunned athletics fans when he hacked 0.11 seconds off his previous world record for the 100-metre sprint. But what's the ultimate human speed limit? Intrigued by this question, Mark Denny at Stanford University, California, decided to work out how fast a human could possibly sprint 100 metres. He examined previous records for various athletics competitions - and greyhound and horse races for good measure - since the 1920s, and found that performances in many events followed a similar pattern, improving steadily until they reached a plateau. Horses in the Kentucky Derby, for example, appeared to approach their speed limit in 1949. Since then any improvements have become minimal and increasingly rare.

Human athletes, too, seem to follow this pattern. Timings for the women's 100 metres approached a plateau in 1977. Male sprinters are still improving, but having constructed a model based on other events, Denny says they too seem on the verge of topping out. He predicts an absolute limit of 9.48 seconds for the 100 metres, just 0.1 seconds under Bolt's current record. "If he keeps on course he will soon come close to the absolute limit," says Denny.

What gives rise to this human speed limit? Denny reckons it's as simple as the athlete's power-to -weight ratio. Beyond a certain point, the benefits of stronger muscles and longer limbs will be offset by the increased energy required to shift the greater load.
原文来源:英国《新科学家》
http://www.newscientist.com/spec ... mans-to-destruction

iavjssssmqee · 发表于 2010-5-4 19:00:20

我们拥有向人类极限挑战并创造纪录的无法抑制的渴望。然而，我们在心理和生理上距离最终极限又有多远呢？
1. 人类的速度极限是多少？

牙买加飞人博尔特在2009年柏林世锦赛打破世界百米纪录摘金，又将由他自己保持的世界纪录提高了0.11秒。人类的速度极限究竟是多少？美国斯坦福大学的马克-丹尼(Mark Denny)对这个问题十分好奇，决定对人类百米速度究竟有多快进行深入探究。

他通过分析1920年以来各种田径比赛(甚至包括赛马之类的比赛)的世界记录，发现许多比赛的成绩都遵循类似的模式，即成绩逐步提高直至稳定。例如肯塔基赛马会，许多参赛马匹在1949年达到速度极限之后就很难再有突破。

人类运动员看上去一样遵循这个模式。女子百米成绩在1977年趋于稳定，男子短跑成绩仍然在提高，不过丹尼表示，基于其它赛事所建立的模型，这一成绩看上去也快到达极限。根据他的预测，男子百米成绩的极限是9.48秒，只比博尔特当前世界记录少0.1秒。丹尼说：“如果继续保持现在这种势头，博尔特不久便会接近于这个极限。”

是什么原因产生的这个人类速度极限？丹尼认为，原因类似于运动员的力量-重量比。超过某个点，更强健肌肉和更长四肢的优势将会被举起更重重物所增加的能量消耗所抵消。

iavjssssmqee · 发表于 2010-5-4 19:00:48

2 How long can we concentrate for?

It's a challenge that most of us have faced when up against an essay deadline, a late-night crisis in the office or perhaps a long car drive. Just how long can we push ourselves mentally before our brain needs a break?

For people in jobs where concentration is critical, like truck drivers, power-plant operators or airline pilots, a 12-hour shift is the limit for most. But pity doctors: complex surgery can go on for hours longer than that, although the lengthiest operations tend to be shared by more than one team.

Until 2004, doctors in the UK on weekend shifts used to work from Friday morning to Monday evening - that's 80 hours in total. At best they would snatch a few hours of sleep; at worst, none at all. "You could be working the vast majority of that time," recalls Helen Fernandes, a neurosurgeon at Addenbrooke's Hospital in Cambridge, UK.

Our powers of concentration decline as the hours tick away. We become less efficient, and take longer to make decisions and to sound the alarm when things go wrong. "Vigilance is one of the areas most sensitive to fatigue," says neuroscientist David Dinges at the University of Pennsylvania in Philadelphia.

Dinges's team used MRI to study the brains of people doing a vigilance task. As people's reaction times slowed, activity in certain brain areas waned. Dinges found that performance in the test
could be predicted from the level of blood flow in the subjects' right fronto-parietal network.

iavjssssmqee · 发表于 2010-5-4 19:01:21

2.人类的注意力能坚持多长时间？

专注是我们大多数人在最后期限之前完成论文、加班到深夜以及长途驱车时所面临的挑战。在大脑需要休息前，我们在心理上究竟要坚持多久？对于那些需要全神贯注从事某项工作的人来说，如卡车司机、发电厂操作人员以及航班驾驶员，12小时是个极限。但是，对于医生而言，复杂的外科手术有时会超过12小时，虽然时间最长的手术往往由不止一个团队分担。

2004年以前，周末班的英国医生要从周五早晨一直上到周日晚上，总共要工作80个小时。他们至多只能睡上几个小时，在最糟糕的情况下，他们甚至80个小时没合过眼。据英国剑桥市艾登布鲁克斯医院神经外科医生海伦-费尔南德斯回忆：“你可能在绝大部分时间里都在工作。”

随着时间推移，我们的注意力也会跟着下降。结果工作效率更低，决策时间更长，失误开始增多。美国宾夕法尼亚大学神经系统科学家戴维-丁格斯(David Dinges)说：“警觉是让人最易疲劳的方面之一。”丁格斯的研究团队利用核磁共振成像技术研究了从事警觉度非常高的工作者的大脑。随着人们反应变得迟钝，某些大脑部位的活动减少。丁格斯发现，根据参与者右额顶骨的血流量，可以预测他们在测试中的成绩。

iavjssssmqee · 发表于 2010-5-4 19:01:38

3 How long could you survive a vacuum?

Sadly we know how long humans can survive if suddenly exposed to the vacuum of space. Three Soviet cosmonauts died in 1971 when a faulty valve caused their Soyuz 11 capsule to depressurise at an altitude of 168 kilometres, shortly before re-entry into the Earth's atmosphere. Investigations revealed that the cabin pressure dropped to zero for 11 minutes and 40 seconds, until the capsule hit the atmosphere. The crew died within 30 to 40 seconds from hypoxia. "You need both oxygen and air pressure to deliver oxygen to the brain," says Jonathan Clark, a former space shuttle crew surgeon.

It is possible to recover from shorter spells in a vacuum, however. In 1966 a NASA technician was testing a spacesuit in a vacuum chamber when the pressure dropped to the level you would experience at an altitude of 36,500 metres. He passed out after 12 to 15 seconds. The last thing he recalled was the saliva boiling off his tongue; that's because water vaporises at low pressure. He regained consciousness within 27 seconds when the chamber was repressurised to the equivalent of an altitude of 4200 metres. Although he was pale, he suffered no adverse health effects.

When the external pressure reduces, gas bubbles form in the blood, leading to lung damage within minutes. And the nervous system can be damaged within hours due to nitrogen dissolving out of the blood. A sudden drop in pressure can be evastating: air trapped in the lungs explodes within seconds. However, if you approach near-vacuum in a more gentle fashion and with intensive medical care standing by, it is possible to survive up to a minute, says Clark.

3.人在真空状态下能活多久？

遗憾的是，我们确实知道人在突然暴露在真空状态下能活多长时间。1971年，苏联联盟11号飞船在重返地球大气层前的一刻，一个故障阀门在168公里的高空令飞船突然减压，造成机上3名宇航员全部遇难。事后调查发现，联盟11号飞船压力突然降至零，这一情况持续了11分40秒，直至它重返大气层。宇航员因缺氧在30到40秒钟后就已死亡。美宇航局航天飞机任务前机组成员乔纳森-克拉克说：“你需要氧气和空气压力这两个因素才能将氧气送入大脑。”不过，如果身在真空环境下时间更短，还有可能抢救过来。

1966年，美宇航局一名技术人员正在真空室测试太空服，这时，室内压力突然降至我们在3.65万米高空才遇到的水平。他在12至15秒内失去知觉。他所能记起的最后一件事是，舌头上的唾液汽化了，这是因为水在低压条件下会蒸发。27秒钟时，真空室的压力重新回到相当于4200米高空的水平，那名技术人员幸运地恢复了知觉。虽然脸色苍白，但他的健康没有遭受任何不利影响。

当外部压力降低，血液中形成气泡，肺部会在几分钟内受损。由于氮气从血液溶出，神经系统在数小时内会受损。压力骤降对人体是致命的：渗入肺部的空气会在几秒钟内爆炸。但是，据克拉克介绍，如果以更适当的方式进入近乎真空的状态，且身边有强化医疗监护服务团队，我们有可能会存活最多一分钟的时间。

iavjssssmqee · 发表于 2010-5-4 19:01:59

4 How much can we remember?

Remembering an 11-digit telephone number is hard enough for most of us. Yet one of the current record-holders for a feat of memory, Chao Lu of China, was able to accurately recite 67,890 digits of pi from memory in 2005. But is that a mere drop in the ocean compared to the brain's true capacity?

Our ability to absorb information is vast. In 1986 Thomas Landauer, then at Bell Communications Research in Morristown, New Jersey, looked at studies of how much visual and verbal information subjects stored while examining images and text, and how quickly they forgot it. This led him to estimate that the average adult stores around 125 megabytes of this type of information in their lifetime - enough to store the contents of 100 books the length of Moby Dick.

Accurately memorising a long string of digits in the correct order is a more demanding task than memorising ad hoc facts about a text or a picture. To discover the limit of the length of a single memory, it may be more informative to consider the techniques used by the memory champions.

Many of them use a mnemonic method. Before starting to memorise a number, they associate a person or object with each four-digit number from 0000 to 9999. The digits of pi can then be translated into a sequence of these people and objects, which the memoriser links by making up a story. This helps add interest to the random sequence of numbers and pegs down the memory.

Lu takes roughly 1000 hours to memorise 40,000 digits. Assuming this rate would apply no matter how big the memory feat, someone who started memorising a number at the age of 20 and spent 12 hours a day at it, every day, would be able to remember around 8,760,000 digits by their 70th birthday.

4.人类究竟能记住多少东西？

记住11位数的电话号码对我们大多数人来说已是很难，但当前的世界记忆冠军、中国的吕超2005年能背诵圆周率67890位。难道与大脑的真正能力相比，这真的不过是沧海一粟？

我们信息接受能力相当强大。1986年在新泽西莫里斯顿的贝尔通信研究公司工作的托马斯·兰德尔研究了人们在看图片和信息时能存储多少视觉和口头信息以及他们忘记的速度有多快。经过研究，他估计，成年人一生中可储存约125M的这种信息，相当于100本《白鲸记》。

按照正确顺序准确无误地记忆一长串数字比记忆短信或者图片更难。要探索记忆长度的极限，考虑记忆冠军使用的技巧可能很有帮助。他们中很多人使用一种记忆方法。在开始记忆数字前，他们会将从0000到9999的每个四位数与人或者物体联系起来。于是，圆周率的数字就被转化为这些人或物的序列，通过编造一个故事让这些人或物联系起来。这样还能增强无序数字的趣味性，而且巩固了记忆。

吕超记忆40000位圆周率大约用了1000小时。不管记忆力有多优秀，假设按照这一比率，一个人从20岁开始背诵圆周率，每天用12个小时，那么到70岁生日的时候，他就能背诵约876万位。

iavjssssmqee · 发表于 2010-5-4 19:02:15

5 How cold can you get and live?

Humans hate being cold, and for good reason: our long-limbed bodies are exquisitely adapted to lose heat, not to retain it. This makes perfect sense in the intense heat of the African savannah, where humans evolved. Without our technological adaptations to cold - clothing, heating, shelter - that's where we'd all still be living, says Mike Tipton of the University of Portsmouth, UK,who studies human thermoregulation.

Surviving the cold is all about protecting core body temperature. This is usually at 37 °C, but it takes surprisingly little for it to start dropping. An ambient temperature of 20 °C can induce hypothermia if conditions are wet and windy, says François Haman, a physiologist at the University of Ottawa, Canada.

When cold, the body starts to shiver and shuts down blood flow to the extremities. If core temperature falls by just 2 °C, hypothermia sets in: first we start to lose consciousness, then the heart loses rhythm. Death follows at about 24 °C, when the heart stops. Usually.

People have been known to survive much lower core body temperatures. Anna Bagenholm survived the biggest drop ever recorded, to 13.7 °C, when she fell into a part-frozen stream and became trapped under ice for 80 minutes.

The constant flow of icy water cooled her body to such an extent that by the time her breathing and heart had stopped, her brain needed very little oxygen in order to survive, giving her the chance of complete recovery.

5.人类能忍受多低的温度？

人类讨厌寒冷是有原因的：我们的肢体较长，这容易散热，不易保存热量。在人类最早进化的酷热的非洲大草原，长长的肢体有很重要的意义。研究人类体温调节的英国朴次茅斯大学的迈克·蒂皮顿指出，即使没有御寒的手段——衣物、暖气和房子，我们所有人仍能生活。

在寒冷中活下来就要保护核心体温。人的核心体温为37摄氏度，但是它降低的速度令人惊讶。加拿大渥太华大学的生理学家弗兰·奥斯哈曼表示，如果在又潮湿又刮风的情况下，20摄氏度的环境温度就能引起体温过低。寒冷的时候，身体开始颤抖，血液停止流向四肢。只要核心体温降低2度就会发生体温过低：首先人们开始失去知觉，然后心跳失率。大约24度时心跳就会停止，人会死亡。但是有人可在核心体温明显降低的情况下活下来。

安娜·巴根霍姆就是这样的人，她的体温曾降到13.7摄氏度仍活着，当时，她不慎落入一个冰冷的溪流中，被困80分钟后才得救。

流动的冰水让她的身体冷到了这样一个温度：呼吸停止，心跳停止，大脑基本上不需要氧气，这让她拥有了完全康复的机会。

iavjssssmqee · 发表于 2010-5-4 19:02:33

6 How long could you survive without food or drink?

How long can a human survive without food or water? In theory, when you finally run out of body fat, protein and carbohydrates, your body runs out of energy and stops functioning. Jeremy Powell-Tuck, a retired clinician who fed David Blaine after his starvation stunt in London in 2003, isn't so sure that this is the lethal point. "You're more likely to die before then," he says. Fat people would only be able to survive for longer if they had enough vital water-soluble B vitamins in their system to help metabolise fat stores. So it is possible that a person could die of starvation and still be fat.

The longest recorded starvation was by the Irish hunger-striker Kieran Doherty in 1981, who died after fasting for 73 days. With a supply of vitamins and water, people have been known to survive over a year without eating. "It used to be a very fashionable way of losing weight around 30 years ago," says Powell-Tuck.

With vitamins but without water, survival time is sharply reduced. A human can be expected to survive for weeks without food, but a thirsty person deprived of water would last a matter of days. "It depends on the rate of water loss," says Michael Sawka at the US Army Research Institute of Environmental Medicine in Natick, Massachusetts. Without water, the volume of blood in your body drops, and with it your blood pressure. Blood becomes thicker and stickier, making it harder to pump around the body, so your heart rate increases to compensate. Even in a cool environment, you wouldn't last for more than a week without water.

6.不吃不喝能活多久？

没有水和食物人类能生存多久？理论上，如果你最后耗光了体脂肪、蛋白质和碳水化合物，你的身体就会因能量耗尽而停止工作。2003年大卫·布莱恩伦敦绝食表演后恢复进餐时的营养指导医生杰里米·鲍威尔·泰克认为，人类死亡不需要等能量完全耗尽：“你可能在之前就死了。”如果体内有足够的水溶性B族维生素来帮助储备脂肪新陈代谢的话，胖人可能会活得更长。因此，人们饿死的时候身体里仍有脂肪也是完全可以的。

最长时不进食记录者是1981年爱尔兰绝食抗议者基兰·多尔蒂，他在绝食73天后死去。在补充维生素和水的情况下，人们可以不吃东西活一年。鲍威尔·泰克说：“大约30年前这是一种非常流行的减肥方法。”

只有维生素而没有水的情况下，存活时间会大大缩短。一个人可以在没有食物的情况下活数周，但是一个干渴脱水的人只能坚持几天。马萨诸塞美国陆军环境医学研究所的迈克尔·萨瓦卡说：“这取决于水流失的速度。”没有水的情况下，身体中血液量会降低，血压也会随之降低。血液变得越来越粘稠，使得血液在身体中的循环变得越来越难，人们的心率就会增大以做出补偿。即使在寒冷的环境中，没有水，人们也只能坚持一周左右。

iavjssssmqee · 发表于 2010-5-4 19:02:50

7 How long can you go without sleep?

On 28 December 1963, Randy Gardner, a 17-year-old schoolboy in San Diego, California, got up at 6 am feeling wide awake and raring to go. He didn't go back to sleep again until the morning of 8 January 1964. That's 11 days without sleep.

Gardner's 264 hours remains the longest scientifically verified period without sleep, breaking the previous record of 260 hours. It was described in a 1965 paper by sleep researcher William Dement of the Stanford University School of Medicine in California, who stayed awake with Gardner for the final three days.

Gardner experienced mood swings, memory and attention lapses, loss of coordination, slurred speech and hallucinations, but was otherwise fine. His first sleep after those 11 days lasted just 14 hours.

According to Dement, Gardner did not consume any stimulants during his "wakeathon". He did, however, have people around him keeping him awake. Without such help you would be fighting hard to stay awake after 36 hours, and would find the urge to sleep near-irrepressible by 48.

But you'd probably be snatching subtle bursts of sleep even before you finally went to bed: sleep -deprived people slip in and out of "microsleeps" - seconds of sleep that occur without you noticing them, often with your eyes open.

Microsleeps aside, how long could Gardner have gone on for? Nobody knows for sure, but we do know that sleep deprivation is eventually fatal. Rats that are kept awake die after two weeks, less time than it takes them to starve to death.

There are no records of a human having been intentionally kept awake long enough to kill them, but a hereditary disease called fatal familial insomnia suggests there is an ultimate limit. The disease eventually robs victims of the ability to sleep. Death follows within three months.

7.人类不睡觉能坚持多久？

1963年12月28日，加利福尼亚州圣地亚哥的17岁在校生兰迪·加德纳早上6点起床，他感觉精神饱满，这样一直持续到1964年1月8日他才再次进入梦乡，也就是说他有11天没睡觉。加德纳打破之前创下的260小时不眠记录后，他创下的264小时记录至今仍是科学验证过的最长的不睡觉时长。加利福尼亚州斯坦福大学医学院的研究人员威廉·德门特在1965年的一篇论文中讲述了这个故事，他在加德纳保持不睡的最后三天一直陪着他。

加德纳经历了情绪波动、记忆和注意力问题、协调能力缺失、说话含糊不清并产生了幻觉，不过他其他方面一切正常。经过这11一天后，他第一觉仅持续了14小时。据德门特说，加德纳在这段持续不眠的过程中并没服用兴奋剂。不过确实有人陪在他身边，让他保持清醒。如果没有别人帮助，你在36小时后就必须努力克制自己不去睡觉，48小时后你就会觉得无法抗拒睡觉的欲望。

然而在你最终上床睡觉之前，你可能已经睡了几个“微型觉”了：缺乏睡眠的人会时不时陷入“微型觉”——当你不注意时，你会在几秒钟内陷入睡眠状态，这期间你经常是睁着眼睛。避开微型睡眠不谈，加德纳最终能坚持多久呢？这个问题没人知道，但是我们清楚，睡眠剥夺最终会导致死亡。迫使老鼠两周不睡觉，它们就会死亡，这比它们饿死所需的时间还短。

没有记录显示一个人故意保持清醒直到死亡的，但是一种被称作致死性家族性失眠症的遗传疾病，说明人类不睡觉的时间是有最大限度的。这种疾病最终剥夺了患者的睡眠能力，使他们在3个月内死亡。

iavjssssmqee · 发表于 2010-5-4 19:03:06

8 How many gs can you pull?

The swooping, sickening sensations you experience on a roller coaster come courtesy of brief g-forces of up to 5 g. Rides have to be designed so people don't black out.

Our tolerance of g-forces depends not only on the magnitude and duration of the acceleration or deceleration but also on the orientation of our body. We are most vulnerable to a force acting towards the feet, because this sends blood away from the brain. Five to 10 seconds at 4 to 5 g vertically typically leads to tunnel vision and then loss of consciousness.

Fighter jets can pull up to 9 g vertically, and the more a pilot can take without blacking out, the better their chances in a dogfight. Some pilots wear "g-suits" which help push the blood away from their legs and towards the brain. People with the highest g tolerance are known as "g-monsters". "We have had people who have been perfectly conscious at 6 g," says physiologist Alec Stevenson of UK-based defence firm Qinetiq. Others pass out at 3 g, he says.

Pilots can boost their natural g tolerance by training inside centrifuges, like the one Qinetiq has in Farnborough in Hampshire. They learn to tense their leg and abdominal muscles to push blood to the upper body, and to breathe in a special way, straining hard as if defecating when constipated, to raise blood pressure.

The greatest vertical force anyone has withstood is 31.25 g, although for that the subject, NASA doctor R. Flanagan Gray was in a special water tank that pressurised his body to help him take the g's. US air force pioneer John Stapp holds the record for highest horizontal acceleration, set in a series of rocket-sledge experiments in the late 1940s. In one test he withstood 46.2 g.

8.普通人能承受多大重力加速度？

过山车俯冲而下时，我们会在很短的时间里承受5g重力加速度，这时我们会产生头晕恶心的感觉。座椅必须经过特殊设计，人们才不会晕过去。我们承受重力加速度的能力，不仅取决于加速度或减速度的变化和持续时间，而且取决于我们身体的方向。我们对朝脚的方向施加的外力最敏感，因为这使血液流向大脑。身体处于垂直状态在4到5g的环境下持续5到10秒，经常就会引起管状视，然后失去知觉。

战斗机在垂直状态的重力加速度可达9g，飞行员承受这种环境的能力越强，对空中作战越有利。一些飞行员穿着“重力加速度服”，这种衣服可避免腿部的血液大量涌向头部。重力承受能力最强的人被称作“怪物g”。总部设在英国的防务公司Qinetiq的生物学家亚力克·史蒂文森说：“我们有些人确实能在6g的环境下保持清醒状态。”其他一些人在3g的环境下就会晕过去。

飞行员通过在离心机里进行训练，可以提高他们承受重力的天然耐受性，Qinetiq在英国汉普郡法恩伯勒就有一台这样的离心机。他们学着收紧腿和腹部肌肉，促使血液流向上半身，并通过特殊呼吸方法降低血压。人们能承受的最大重力是31.25g，不过为了达到这个目的，美国宇航局的医生弗拉纳根·格雷进入一个特制水箱，这个水箱给他的身体施加压力，帮助他承受住那么大的重力加速度。美国空军先驱约翰·斯塔普保持着最高的水平重力加速度纪录。

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