Exercise and addiction
People, it seems, have evolved to be addicted to exercise
AS THE legions of gym bunnies and jogging enthusiasts who race out into the spring sunshine every year clearly demonstrate, running can be fun. More specifically, running triggers the release of brain chemicals called endocannabinoids that create a potent feeling of pleasure. As their name suggests, these endocannabinoids work in the same way as the active ingredient of marijuana.
每年春天都有大批的健身爱好者和跑步爱好者们走出家门，奔跑在阳光之下，由此可见，跑步可以带来乐趣。更确切的说，跑步能激发大脑分泌一种叫做内源性大麻素的化学物质，它能产生强烈的愉悦感 。就像它们的名字那样，这些内源性大麻素和大麻的活性成分拥有同样功效 。
legions of：大批的 Legions of birds 一大群鸟 endocannabinoids：内源性大麻素
From an evolutionary standpoint this surge of endocannabinoids, and the “runner’s high” it creates, make sense. For ancient humans, remaining fit enough to run after game and away from predators and enemies was vital for survival. Yet whether other mammals are also driven to exercise by endocannabinoids has remained a mystery. Now a study led by David Raichlen of the University of Arizona has revealed that the runner’s high does exist in other species, but not in all.
从进化角度来看，这种内源性大麻素的增多，以及由它引起的“跑步者的亢奋情绪”是有道理可循的。对于古人来说，能在游戏之后还有足够的体力奔跑，逃离掠夺者和敌人是生存下去的根本 。然而，其他哺乳动物是否也是因内源性大麻素而进行锻炼就不得而知了 。现在，亚利桑那州的戴维•瑞奇连做了一项研究，揭示出奔跑者的亢奋情绪还存在于其他一些物种身上，并非全部都有 。
Dr Raichlen hypothesised that endocannabinoid-driven exercise highs would be found in those mammals that gain an evolutionary benefit from being fast on their feet: antelopes, horses and wolves, for example. However, he also thought that they would not be present in those which are known for being quick and agile, but not for running, like ferrets. To test these ideas, he and a team of colleagues devised an experiment that monitored the endocannabinoid levels of different species after they had been walking or running on a treadmill.
瑞奇连博士进行假设，由内源性大麻素引起的锻炼亢奋情绪可能同样会发生在那些足部进化较快的哺乳动物身上，如羚羊、马和狼。但是，他还认为这些情绪不会出现在像雪貂这样快速灵活却不善长跑步的动物身上 。为了验证这些观点，他和一组同事设计了一个试验，观察不同的物种在跑步机上走或跑过一段路程后，各自内源性大麻素的变化情况 。
The experimental animals in question were ten people, eight dogs and eight ferrets. Dr Raichlen had them run or walk on the treadmill for 30 minutes. Since running and walking speeds differ from species to species, the speed at which the treadmill moved was varied so that it raised the heart rates of the different participants to the same level. Running speeds were thus set at 2.5 metres a second for people, 1.83 for dogs and 0.84 for ferrets. Walking speeds were set at 1.25 metres a second for people and 1.1 for dogs. The ferrets proved too easily distracted to walk consistently on the treadmills and were thus left to sit quietly in their cages for this part of the study. Each participating animal ran for one session and walked for one other, and did so on separate days, to avoid exhaustion. Before and after each session, blood was drawn from each and the endocannabinoid levels in it were measured.
试验用到的动物是十个人、八条狗和八只雪貂。瑞奇连博士让他们各自在跑步机上或走或跑上30分钟 。由于不同物种走或跑的速度不同，跑步机设定的速率也要因人而异，因此他们的心跳速度会上升到一个相同的高度 。人每秒的奔跑速率设为2.5米，狗为每秒1.83米，雪貂为每秒0.84米 。人每秒的步行速度为1.25米，狗为1.1米 。事实证明雪貂无法坚持在跑步机上保持行走，所以这部分研究他们只能静静的呆在笼子里 。每个参与者都要分别走上和跑上一段，但是这两段路程需分开进行以免过度疲劳 。每段路程的开始和结束都要进行抽血，以此判断他们体内内源性大麻素的含量 。
The researchers report in the Journal of Experimental Biology that, after 30 minutes of walking (or sitting in a cage), participants’ endocannabinoid levels did not rise. After running, however, the average human’s endocannabinoid levels rose from 2.4 picomoles per millilitre (pmol/ml) to 6.1. Dogs showed a similar trend, with levels rising from 2.4 pmol/ml to 8.0. Ferrets were different. Although they did show an increase, from 3.0 to 3.9 pmol/ml, this was not a statistically significant rise. These findings suggest that dogs experience a “runner’s high” but ferrets do not.
研究者们在《试验生物学杂志》上发表报告称，30分钟的步行（或笼中静坐）后，参与者的内源性大麻素含量都没有升高。但是，跑步后，人体内的内源性大麻素平均含量从每毫升2.4皮摩尔上升到6.1皮摩尔 。狗体内的内源性大麻素也从2.4皮摩尔上升到8.0皮摩尔 。不同的是，尽管雪貂的内源性大麻素也有所上升，但只从3.0上升到3.9，从统计学上看，这并不是很高的数值 。这些发现表明，狗会产生“跑步者的亢奋情绪”，而雪貂却不会 。
Dr Raichlen argues that it makes sense for ferrets not to have systems that reward cardiovascular activity, since such exercise consumes a lot of energy, may cause injury, and is not crucial to the stealthy hunting technique of sneaking down burrows and killing rabbits in their sleep. What is not clear is whether the endocannabinoid reward is an ancient mechanism that has been lost on branches of the mammalian tree that do not need it, or is something that evolves quickly in species which become active. Given that humanity’s arboreal simian ancestors would presumably have had little need to run, it is probably the latter. But to be sure Dr Raichlen will need to put animals far less co-operative than ferrets on the treadmill.
瑞奇连博士认为，雪貂在进行过心脑血管运动后，体内没有补偿性的机制是有原因的，因为这些运动会消耗太多能量，有可能使他们受伤，而且它们常常小心翼翼的潜入洞穴，在熟睡中就将兔子们杀死，这些运动对他们来说毫无意义。但是，内源性大麻素是否曾经存在于远古物种的体内，只是由于不再需要而在某些哺乳动物科身上消失了，还是它仅仅在某些活跃的物种加速进化过程中产生，这些都不得而知 。假设人类生活在丛林中的猿类祖先没有奔跑的需要，则后者很有可能是事实 。但是为了证实这一点，瑞奇连博士需要再把一些和雪貂不同的动物放上跑步机 。