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.’

參考譯文：
合理的體育鍛煉可以幫助我們放松心情，這一點眾所周知，但是其原理卻不明確。最近，來自瑞典的科學家給出了答案：精心訓練的肌肉似乎可以象肝臟清除體內毒物一樣，濾掉造成壓力的化學物質，阻止它們到達大腦而起作用。

這一發現并不僅僅有助于解釋為什么運動可以減輕壓力，也可能導致開發出抑郁癥的新療法。

來自瑞典斯德哥爾摩卡羅林斯卡醫學院研究人員把兩組小鼠暴露在巨響和燈光閃爍的環境中，并剝奪它們的睡眠時間，導致它們處于壓力狀態。

5周后，正常的小鼠表現出抑郁癥跡象，包括食欲不振。但是轉基因組小鼠卻保持了健康狀態，這組小鼠通過了基因修飾，幫助它們即使不運動也能保持強健發達的肌肉。

進一步的實驗揭開了其中奧秘：原來強健的肌肉可以產生更多被稱為KATS的保護性蛋白，這種酶可以分解清除血液中的被稱為犬尿氨酸的應激化學物質，組織它們進入大腦而導致抑郁癥狀。

當研究人員給予犬尿氨酸，正常的小鼠很快變得沮喪，證明這種化學物質的確可以導致抑郁癥狀發生。

但是，肌肉發達的小鼠卻對該化學物質不敏感。研究人員發現，事實上，肌肉發達的小鼠血液犬尿氨酸含量一直沒有升高，原因是肌肉產生的KATS酶可以迅速分解破壞犬尿氨酸。

另外的實驗表明，正常小鼠通過規律性踏車運動可以產生更多保護性KATS。

重要的是，人只需要幾個星期鍛煉便可以產生大量KATS。

這項研究表明，肌肉可以具有類似肝臟和腎臟一樣的神奇的解毒功能，訓練有素的肌肉通過產生保護性酶來清除血液中應激性化學物質起到保護大腦的作用。

研究人員進一步解釋說，這一發現除了從原理上證實運動可以幫助人們緩解壓力，還可能會導致抗抑郁癥新療法的產生。

這項研究最新發表在《細胞》雜志上。

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