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Is there a limit to human endurance? Science says yes

人的耐力是否有限？科學(xué)證實，確實如此

上海譯銳翻譯     2019-6-11    10:44 a.m.

圖片來源：? 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.

從鐵人三項到環(huán)法自行車賽，即使是忍耐力最強的運動選手，其耐力極限也會受到某些比賽的考驗。目前，一項針對世界某些距離最長、最殘酷的體育賽事的能量消耗研究表明，無論是什么活動，任何人都會達到同樣的代謝極限，即一個人可以長時間所承受的、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.

當(dāng)談到持續(xù)數(shù)天、數(shù)星期以及數(shù)月的體力活動，研究人員發(fā)現(xiàn)，人類所能燃燒的卡路里僅為其靜止代謝率的2.5倍。

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

研究人員發(fā)現(xiàn)，即使是全球奔跑速度最快的超級馬拉松選手也無法超越這一極限。

"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、杜克大學(xué)進化人類學(xué)助教Herman Pontzer表示：“這就確定了人類可能實現(xiàn)的范圍領(lǐng)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.

研究人員發(fā)現(xiàn)，當(dāng)超越人體靜止代謝率2.5倍這一極限時，人體內(nèi)部的細胞開始破裂，以補償卡路里的不足。

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.

來自蘇格蘭的阿伯丁大學(xué)和中國科學(xué)院，同時也是團隊領(lǐng)導(dǎo)者的Pontzer和John Speakman表示，極限的一個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.

換句話說，吃的再多也未必能夠幫助人們在阿拉斯加愛迪塔羅德（Iditarod）狗拉雪橇大賽中創(chuàng)造歷史。我們的腸道每天能夠有效吸收多少熱量是有一個極限的。

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

結(jié)果將會于6月5日在《走近科學(xué)》線上版公布。

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.

針對研究，研究團隊測量了一組運動員每天消耗的卡路里。作為2015橫越美國自行車賽（從加州到華盛頓，比賽行程為3000英里）的一部分，這群運動員在5個月的時間內(nèi)每周會跑5次馬拉松。研究團隊還考慮了人類耐受力的其他方面，包括艱難的100米越野賽和懷孕。

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.

經(jīng)過一段時間繪制數(shù)據(jù)后，研究團隊發(fā)現(xiàn)了L形曲線。運動員的體能消耗一開始會比較高，但是在剩余的比賽中，體能消耗不可避免地大幅下降并會在體能消耗達到其基礎(chǔ)代謝率的2.5倍時筋疲力盡。

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.

研究項目的共同作者Caitlin Thurber對橫越美國自行車賽第一名和最后一名選手的尿樣進行分析。經(jīng)過20周的接力馬拉松后，運動員一天所燃燒的卡路里要比預(yù)期少600。研究結(jié)果表明，身體會調(diào)低新陳代謝以幫助身體保持在一個可持續(xù)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：“這是被動能量消耗的一個很好例證。在被動能量消耗中，身體無法在延長的時間內(nèi)將能量消耗保持在一個極高的水平。”

"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米沖刺，但是如果跑數(shù)英里的話，你只可以慢跑，對不對？這里也是這個道理。”

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.

所有的耐力賽都遵循了同樣的L形曲線，無論運動員在低于冰點的溫度下數(shù)日拖著500磅的雪橇穿越南極洲，還是在夏日參加環(huán)法自行車賽。這項研究結(jié)果對之前研究人員的說法提出質(zhì)疑。根據(jù)之前研究人員的說法，人類的耐受力與調(diào)節(jié)身體溫度的能力有關(guān)。

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.

研究人員發(fā)現(xiàn)，耐力賽的一個限制因素是消化過程，即身體處理食物并吸收卡路里和營養(yǎng)物質(zhì)以為身體代謝提供動力的能力。

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，耐力運動員最極限的可持續(xù)能量消耗僅比女性在孕期所承受的新陳代謝率高一點。這表明，使比如鐵人三項運動員無法打破速度記錄的相同生理極限也可能會對生命的其他方面進行限制，比如寶寶可以在子宮內(nèi)長到多大。

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."

據(jù)研究人員了解，沒有人能夠超越這一極限。Pontzer表示：“所以我猜，對于出類拔萃的耐力運動員，這是一項挑戰(zhàn)。當(dāng)你被證明是錯誤的時，科學(xué)會發(fā)揮作用。也許某一天，有人會突破這一限制并讓我們知道我們的不足。”

需要了解的詞匯：

To surpass the limit：超越極限

Ironman triathlon：鐵人三項

Tour de France：環(huán)法自行車賽

energy expenditure：能量消耗

Exertion：用力

Flat out：筋疲力盡

文章來源：科學(xué)日報，編輯：質(zhì)控部Susan