运动不要多喝水?

Endurance athletes such as runners and cyclists are used to hearing injunctions to drink enough water. While staying hydrated is important, there are times when you can have too much water.

跑步和自行车等耐力运动的运动员已习惯于听到要补充足够水分的劝告。尽管保持身体有足够水分很重要，但有时候你可能会摄入过多的水分。

Last summer, for example, I began experiencing unusual muscle cramping in my hands and legs long after I finished a run, even the next day. Following the usual advice, I increased my water intake and ate bananas, which are full of potassium. That did not fix the problem. I then heard Jordan Metzl, a sports medicine specialist at the Hospital for Special Surgery in New York, describe how he had nearly crashed during his first Ironman race. It was a hot day, Dr Metzl recalled, and he was saved by a bearded bystander who was handing out raw salt.

比如，去年夏天，我开始在跑完步很长时间后（乃至第二天）出现手部和腿部肌肉痉挛。我遵循一般的建议增加了水分摄入，吃富含钾的香蕉。然而问题没有解决。之后我听了纽约特殊外科医院(Hospital for Special Surgery)运动医学专家约尔丹•梅茨尔博士(Jordan Metzl)讲述他在第一次参加铁人三项赛时差点晕倒的事情。梅茨尔回忆，那天天气炎热，一个蓄着胡须、正在分发粗盐的旁观者救了他。

If you follow medical news, you have probably heard the campaigns in the UK and the US warning about eating too much salt. It is true that there is often a lot of salt added to prepared food, and sodium can raise your blood pressure, which can lead to a heart attack.

如果你关注医学方面的新闻，你很可能听说过英美两国旨在警告人们不要摄入太多盐分的宣传活动。的确，预制食品中往往含有大量盐分，钠可能会升高你的血压，高血压可能导致心脏病发作。

But cyclists and runners face an entirely different problem — too little salt, says Dr Metzl, who has run 30 marathons and is the author of a medical guide for athletes calledRunning Strong. When it is hot and humid, most people tend to sweat a lot during exercise. Very fit athletes actually sweat more than other people, which sounds counterintuitive, but it helps cool them down.

但梅茨尔表示，自行车运动员和跑步运动员面临着截然不同的问题——盐分摄入太少。梅茨尔参加过30次马拉松比赛，著有为运动员撰写的医学参考书《跑步者健康指南》(Running Strong)。天气炎热潮湿的时候，大多数人会在锻炼中大量出汗。身体非常健康的运动员实际上会比其他人出汗更多，这听起来似乎有悖直觉，但这其实能够帮助运动员降低体温。

There is also a subgroup of athletes whom Dr Metzl calls “salty sweaters”, who not only sweat more than most during exercise but also sweat much more salt. I know because I am one and my sweat is so salty it sometimes irritates my skin.

在运动员中，有一类人被梅茨尔称为“多盐流汗者”(salty sweaters)，这类人在锻炼中不仅会比大多数人出更多的汗，而且他们的汗液中含盐量也大得多。对此我有亲身体会，我的汗液中含盐量很大，以至于有时候会刺痛我的皮肤。

A natural reaction when you sweat is to drink more water, especially during races when there are water tables by the roadside. But if you are taking in water and not electrolytes, which include sodium, magnesium and potassium, you are making the problem worse. The water dilutes the salt in your blood, which has been reduced by your sweat.

当你流汗的时候，自然反应是喝更多的水，尤其是在那种设置了路边饮水桌的比赛期间。但如果你只摄入水，不摄入钠、镁、钾等电解质，你会使问题变得更糟。水会稀释你血液中本就因为出汗而减少的盐分。

Too little sodium in the blood can cause a condition known as hyponatraemia, which was only identified in 1985. Early symptoms of hyponatraemia are cramps of the small muscles in your hands and feet, like I had, followed by leg cramps. If the problem continues to worsen, you can become mentally disoriented and even, in extreme cases, die.

血液中钠含量过低会导致一种叫做“低钠血症”的病症。人们直到1985年才发现这种病症。低钠血症的早期症状是手脚小肌肉群痉挛，就像我曾经经历过的那样，然后是腿部肌肉痉挛。如果症状持续恶化，你可能会神志不清，在极端情况下甚至可能死亡。

The British Journal of Sports Medicine looked at the problem and urged endurance athletes to ensure they get enough salt during exercise, but also warned that “electrolyte replacement will slow but not prevent the development of hyponatraemia if fluid intake is in gross excess of sweating rate”. In other words, do not drink too much.

《英国运动医学期刊》(British Journal of Sports Medicine)研究了这个问题，并敦促耐力运动员确保他们在训练时摄入足够的盐分，但这份期刊还警告称，“如果液体摄入总量超过出汗量，补充电解质只能减缓、但无法阻止低钠血症的形成”。换句话说，不要喝太多水。

Unfortunately, many of the commercial brands of electrolyte-laden sports drinks are loaded with sugar, which is counterproductive if you are running to stay in shape. Luckily there are electrolyte tablets like High5 Zero and Nuun available that contain sodium but no sugar. Take them well before you start your endurance event and after as well.

遗憾的是，很多商业品牌的电解质运动饮料都含有大量的糖，如果你跑步是为了保持身材，喝这种饮料会适得其反。幸运的是，现在有High5 Zero、Nuun这样含钠但不含糖的电解质片剂。你要在开始耐力运动之前和之后服用这类片剂。

Some people may worry about raising their blood pressure by taking electrolytes; indeed, people with a heart condition should consult their doctor before taking them. But Dr Metzl says that for most endurance athletes, having too little salt in the blood poses a far greater risk than having slightly higher blood pressure for a day or two.

有些人可能会担忧，摄入电解质可能会升高血压；的确，患有心脏疾病的人士应该在服用前咨询他们的医生。但梅茨尔表示，对于大多数耐力运动员而言，比起血压在一两天内略微升高，血液中盐分太少造成的威胁要大得多。