We all know that a good workout helps us relax. Now scientists have worked out why.
It seems that well-honed muscles stop a stress chemical from reaching the brain.
The muscles filter out the dangerous substance, much like the liver removes poisons from the body.
The finding doesn’t just help explain why exercising makes us feel less stressed – it could also lead to new treatments for depression.
The Swedish researchers put two group of mice under stress by exposing them to loud bangs and flashing lights and waking them up at odd times.
After five weeks of this, the normal mice showed signs of depression, including loss of appetite.
However, the second group of GM mice remained healthy.
These mice had genes that meant they were muscly, even without exercising.
Further tests showed what is magical about muscle.
Muscly mice make more of protective proteins called KATs. These stop a stress chemical called kynurenine from travelling to the brain.
The researchers from Stockholm’s Karolinska Institute showed that normal mice quickly become depressed when given kynurenine.
But muscly mice were immune to the chemical.
In fact, the amount of kynurenine in their blood never rose because the KAT enzymes in their bulging muscles quickly neutralised it.
Other experiments showed that normal mice made more of the protective KATs after regularly running on their wheel.
Importantly, people also made more KATs after just a few weeks of exercise.
Researcher Jorge Ruas said that by detoxifying the blood, muscle protects the brain said: ‘Well-trained muscle produces an enzyme that purges the body of harmful substances.
‘The muscle’s function is reminiscent of the kidney or liver.’
Writing in the journal Cell, Dr Ruas said the discovery paves the way for new and better treatments for depression, which affects up to one in five Britons as some point in their life.
Drugs that that works on the muscles, rather than the brain, should produce fewer side-effects.
Dr Ruas said: ‘Depression is a debilitating condition with a profound impact on quality of life for millions of people worldwide.
‘Depression is one the world’s leading causes of disease burden and time lived with disability and current anti-depressant treatments are insufficient.
‘Our work suggests that there is great therapeutic potential…in harnessing one of the many beneficial effects of exercise.’

参考译文：
合理的体育锻炼可以帮助我们放松心情，这一点众所周知，但是其原理却不明确。最近，来自瑞典的科学家给出了答案：精心训练的肌肉似乎可以象肝脏清除体内毒物一样，滤掉造成压力的化学物质，阻止它们到达大脑而起作用。

这一发现并不仅仅有助于解释为什么运动可以减轻压力，也可能导致开发出抑郁症的新疗法。

来自瑞典斯德哥尔摩卡罗林斯卡医学院研究人员把两组小鼠暴露在巨响和灯光闪烁的环境中，并剥夺它们的睡眠时间，导致它们处于压力状态。

5周后，正常的小鼠表现出抑郁症迹象，包括食欲不振。但是转基因组小鼠却保持了健康状态，这组小鼠通过了基因修饰，帮助它们即使不运动也能保持强健发达的肌肉。

进一步的实验揭开了其中奥秘：原来强健的肌肉可以产生更多被称为KATS的保护性蛋白，这种酶可以分解清除血液中的被称为犬尿氨酸的应激化学物质，组织它们进入大脑而导致抑郁症状。

当研究人员给予犬尿氨酸，正常的小鼠很快变得沮丧，证明这种化学物质的确可以导致抑郁症状发生。

但是，肌肉发达的小鼠却对该化学物质不敏感。研究人员发现，事实上，肌肉发达的小鼠血液犬尿氨酸含量一直没有升高，原因是肌肉产生的KATS酶可以迅速分解破坏犬尿氨酸。

另外的实验表明，正常小鼠通过规律性踏车运动可以产生更多保护性KATS。

重要的是，人只需要几个星期锻炼便可以产生大量KATS。

这项研究表明，肌肉可以具有类似肝脏和肾脏一样的神奇的解毒功能，训练有素的肌肉通过产生保护性酶来清除血液中应激性化学物质起到保护大脑的作用。

研究人员进一步解释说，这一发现除了从原理上证实运动可以帮助人们缓解压力，还可能会导致抗抑郁症新疗法的产生。

这项研究最新发表在《细胞》杂志上。

原始来源：http://www.dailymail.co.uk/health/article-2769669/Feeling-anxious-Take-weights-class-Toned-muscles-block-stress-chemicals-reaching-brain.html