Is there a limit to human endurance? Science says yes

人的耐力是否有限？科学证实，确实如此

上海译锐翻译     2019-6-11    10:44 a.m.

图片来源：© babaroga / Adobe Stock

From the Ironman triathlon to the Tour de France, some competitions test the limits of even the toughest endurance athletes. Now, a new study of energy expenditure during some of the world's longest, most grueling sporting events suggests that no matter what the activity, everyone hits the same metabolic limit -- a maximum possible level of exertion that humans can sustain in the long term.

从铁人三项到环法自行车赛，即使是忍耐力最强的运动选手，其耐力极限也会受到某些比赛的考验。目前，一项针对世界某些距离最长、最残酷的体育赛事的能量消耗研究表明，无论是什么活动，任何人都会达到同样的代谢极限，即一个人可以长时间所承受的、最大限度的用力程度。

When it comes to physical activities lasting days, weeks and months, the researchers found, humans can only burn calories at 2.5 times their resting metabolic rate.

当谈到持续数天、数星期以及数月的体力活动，研究人员发现，人类所能燃烧的卡路里仅为其静止代谢率的2.5倍。

Not even the world's fastest ultra-marathoners managed to surpass that limit, the researchers found.

研究人员发现，即使是全球奔跑速度最快的超级马拉松选手也无法超越这一极限。

"This defines the realm of what's possible for humans," said study co-author Herman Pontzer, an associate professor of evolutionary anthropology at Duke University.

研究合著者、杜克大学进化人类学助教Herman Pontzer表示：“这就确定了人类可能实现的范围领域”。

Beyond the threshold of 2.5 times a person's resting metabolic rate, researchers found, the body starts to break down its own tissues to make up for the caloric deficit.

研究人员发现，当超越人体静止代谢率2.5倍这一极限时，人体内部的细胞开始破裂，以补偿卡路里的不足。

One explanation for this limit may be the digestive tract's ability to break down food, said team leaders Pontzer and John Speakman of Scotland's University of Aberdeen and the Chinese Academy of Sciences.

来自苏格兰的阿伯丁大学和中国科学院，同时也是团队领导者的Pontzer和John Speakman表示，极限的一个原因可能是消化道分解食物的能力。

In other words, eating more won't necessarily help someone make Iditarod history. "There's just a limit to how many calories our guts can effectively absorb per day," Pontzer said.

换句话说，吃的再多也未必能够帮助人们在阿拉斯加爱迪塔罗德（Iditarod）狗拉雪橇大赛中创造历史。我们的肠道每天能够有效吸收多少热量是有一个极限的。

The results will appear online June 5 in the journal Science Advances.

结果将会于6月5日在《走近科学》线上版公布。

For the study, the team measured daily calories burned by a group of athletes who ran six marathons a week for five months as part of the 2015 Race Across the USA, a 3,000-mile race from California to Washington, D.C. The team also considered other feats of human endurance, including punishing 100-mile trail races and pregnancy.

针对研究，研究团队测量了一组运动员每天消耗的卡路里。作为2015横越美国自行车赛（从加州到华盛顿，比赛行程为3000英里）的一部分，这群运动员在5个月的时间内每周会跑5次马拉松。研究团队还考虑了人类耐受力的其他方面，包括艰难的100米越野赛和怀孕。

When they plotted the data over time, they found an L-shaped curve. The athletes' energy expenditure started out relatively high, but inevitably plunged and flattened out at 2.5 times their basal metabolic rate for the remainder of the event.

经过一段时间绘制数据后，研究团队发现了L形曲线。运动员的体能消耗一开始会比较高，但是在剩余的比赛中，体能消耗不可避免地大幅下降并会在体能消耗达到其基础代谢率的2.5倍时筋疲力尽。

Co-author Caitlin Thurber analyzed urine samples collected during the first and final legs of Race Across the USA. After 20 weeks of running back-to-back marathons, the athletes were burning 600 fewer calories a day than expected based on their mileage. The findings suggest that the body can "downshift" its metabolism to help stay within sustainable levels.

研究项目的共同作者Caitlin Thurber对横越美国自行车赛第一名和最后一名选手的尿样进行分析。经过20周的接力马拉松后，运动员一天所燃烧的卡路里要比预期少600。研究结果表明，身体会调低新陈代谢以帮助身体保持在一个可持续的水平。

"It's a great example of constrained energy expenditure, where the body is limited in its ability to maintain extremely high levels of energy expenditure for an extended period of time," Thurber said.

Thurber表示：“这是被动能量消耗的一个很好例证。在被动能量消耗中，身体无法在延长的时间内将能量消耗保持在一个极高的水平。”

"You can sprint for 100 meters, but you can jog for miles, right? That's also true here," Pontzer said.

Pontzer表示：“你可以100米冲刺，但是如果跑数英里的话，你只可以慢跑，对不对？这里也是这个道理。”

All the endurance events followed the same L-shaped curve, whether the athletes were hauling 500-pound sleds across Antarctica for days in sub-freezing temperatures, or cycling the Tour de France in summer. That finding challenges the idea, proposed by previous researchers, that human endurance is linked to the ability to regulate body temperature.

所有的耐力赛都遵循了同样的L形曲线，无论运动员在低于冰点的温度下数日拖着500磅的雪橇穿越南极洲，还是在夏日参加环法自行车赛。这项研究结果对之前研究人员的说法提出质疑。根据之前研究人员的说法，人类的耐受力与调节身体温度的能力有关。

One limiting factor for endurance events, researchers found, lies in the digestive process -- the body's ability to process food and absorb calories and nutrients to fuel bodily processes.

研究人员发现，耐力赛的一个限制因素是消化过程，即身体处理食物并吸收卡路里和营养物质以为身体代谢提供动力的能力。

Interestingly, the maximum sustainable energy expenditure found among endurance athletes was only slightly higher than the metabolic rates women sustain during pregnancy. This suggests that the same physiological limits that keep, say, Ironman triathletes from shattering speed records may also constrain other aspects of life too, such as how big babies can grow in the womb.

有趣的是，耐力运动员最极限的可持续能量消耗仅比女性在孕期所承受的新陈代谢率高一点。这表明，使比如铁人三项运动员无法打破速度记录的相同生理极限也可能会对生命的其他方面进行限制，比如宝宝可以在子宫内长到多大。

As far as the researchers know, no one's ever sustained levels beyond this limit. "So I guess it's a challenge to elite endurance athletes," Pontzer said. "Science works when you're proven wrong. Maybe someone will break through that ceiling some day and show us what we're missing."

据研究人员了解，没有人能够超越这一极限。Pontzer表示：“所以我猜，对于出类拔萃的耐力运动员，这是一项挑战。当你被证明是错误的时，科学会发挥作用。也许某一天，有人会突破这一限制并让我们知道我们的不足。”

需要了解的词汇：

To surpass the limit：超越极限

Ironman triathlon：铁人三项

Tour de France：环法自行车赛

energy expenditure：能量消耗

Exertion：用力

Flat out：筋疲力尽

文章来源：科学日报，编辑：质控部Susan