健身增肌的原理是什么？

前 言

现代健身文化鼓舞人们逃求多肌肉，少脂肪，逃求轮廓清楚的身体形态和线条，那意味着安康、强壮、力量、吸引力和人体美。

图1：力训研究所女成员

关于增肌的原理，大大都健身喜好者练了一辈子，增肌增了一辈子，都是稀里糊涂的，良多健身博主/科普者也是一知半解。

听他们讲增肌的原理，一会“适应性增粗”，一会“扯破后超量恢复”，一会“肌肉没有法子被迫生长”，让人觉得捉急，因为那不包罗任何信息量，跟没说一样。

要把原理讲清晰，那就十分复杂了。关键词：卵白量合成、机械张力、细胞信号、DNA转录。

一、大多健身者对卵白量存在曲解

大多说健身者都认为，我们吃下去的卵白量做为原料，来构成我们的肌肉，那显然不合错误，因为那混淆了“卵白量”和“氨基酸”。我们修建身体，用的是氨基酸，不是卵白量。

卵白量由大量的氨基酸和键构成，是构造十分复杂的大分子物量[1]。我们举两个具有代表性的例子。第一个，人体血红卵白（图2）。

图2-1

第二个例子，某些实核生物体内的核糖体卵白。

图2-2图2-3

各人能够看出，卵白量具有极其复杂的构造，我们底子不成能间接利用构造如斯复杂的大分子物量来构建我们的身体，我们得先把卵白量消化、拆分。

在消化和拆分的过程中，人操纵各类胃卵白酶，如胰卵白酶[2][3][4][5]、肠卵白酶[6][7][8][9]等，把食物中的卵白量水解[10][11][12]成为最根本单元——氨基酸[13][14][15]、或多个氨基酸构成的短肽[16][17][18]，然后才气用它们用来修建我们的身体。

二、增肌，到底增是哪里？

良多健身者都能答复：增的是肌纤维。

然后呢？没了。

大大都人都晓得“增粗肌纤维”、增加肌肉中的卵白量合成，但肌纤维是若何变粗的，卵白量合成到底在肌纤维的哪里，却说不清晰。

关于我们来说，起首要搞清晰肌纤维的构造，肌纤维中的卵白量增到了哪里。在一般人的认知中，细胞可能像个球一样，圆圆的，中间是细胞核。

图3：细胞

但肌细胞（肌细胞就是肌纤维）不是个球状的构成，而是像长长的管子一样。肌细胞外表是细胞膜，里面次要有更多更细的“管子”：肌原纤维，它外面包裹着肌浆网，细胞里还有线粒体、细胞核等等。

图4：肌肉构造

我们的肌肉之所以可以收缩，次要是因为肌纤维内的肌原纤维，它的内部含有更多更细的“肌丝”：粗肌丝、细肌丝[5,6]。

肌肉收缩时，在神经系统释放的生物电的刺激下[19][20][21][22]，粗细肌丝之间的“锁”被翻开[23][24][25][26][27]，ATP氧化释放能量，带动粗/细肌丝彼此“滑行”，肌肉缩短，完成收缩[28][29]。

肌动卵白[30][31][32]构成我们肌纤维中的细肌丝，肌球卵白[33][34][35][36]构成粗肌丝。例如人心肌中的肌球卵白复合物：

图5：人心肌中肌球卵白复合物

如今各人应该大白了，所谓增肌，次要增的是肌原纤维上的粗、细肌丝上的卵白。

三、肌原纤维内的卵白量是怎么来的？

许多人简单的认为，肌纤维中的卵白量不就是吃下去的卵白量合成成氨基酸构成的。那个说法没错，但几乎就是废话，因为氨基酸是若何构成卵白量，那才是关键。

与大大都人想象的差别，现实上，卵白量的品种十分多[37][38][39][40]。多到什么水平呢？实核生物一个细胞内的卵白量，就多达几万种。

卵白量的构造十分复杂[41][42][43]，在空间中呈现立体的几何形态[44][45]，具有多层的扭曲和折叠性状[46][47][48][49][50]；只要略微有一点变革，它的功用、特征和不变性就可能发作变革[51][52][53]。

图6：胰岛素降解酶图7：IGF-1受体与胰岛素复合物图8：亚硝酸盐复原酶图9：谷氨酸脱氢酶图10：E3毗连酶泛素

卵白量的构造十分复杂，当然也包罗我们的肌肉。人肌肉里的卵白量是大量氨基酸构成的生物大分子物量[54][55][56][57]，人肌肉的肌球卵白（及其连系物）在仪器的目光下看上去长如许。

图11：人肌球卵白复合物图12：人肌球卵白复合物图13：人肌球卵白复合物

因为人体肌肉中的卵白量构造如斯复杂，那么很显然，大量的氨基酸绝不成能凭白无故的、在没有“指引”的前提下，就能根据某种预先设置好的体例来构建如斯复杂的大分子卵白量。

那就像你有大量的砖石，但是用砖石造造建筑，需要设想图，并非把砖石胡乱堆在一路就是建筑了。氨基酸构成卵白量也是一样的事理。毫无疑问，有什么工具在引导它们。

谜底是mRNA。mRNA好像一条链子，上面预留了差别类型的氨基酸的连系区（密码子）。身体把大量的氨基酸运输过来，每个氨基酸能够对号入座，“组拆”到那条链子上。

图14：mRNA

当然，光是组拆还远远不敷。组拆好了以后，那只是构成了卵白量的雏形罢了，卵白量有四级空间构造，从宏不雅上看，是多重折叠的。例如人体血红卵白，3D看是如许：

图15：人体血红卵白

但是，人体血红卵白，若是用图形暗示，在教科书上，是如许的：

图16：人体血红卵白

仅仅氨基酸“组拆”到mRNA上还不敷，还有折叠[58][59][60][61]、润色[62][63][64][65]、转运[66][67]等许多工做要做；我们把mRNA酿成卵白量（的雏形）那一步，叫做翻译[68][69][70][71][72]。

那mRNA哪来的呢？是DNA以它本身为模板，复造出来的（单螺旋构造）。那一部叫做转录[73][74][75][76]；从DNA到卵白量，宏不雅上次要是转录和翻译那两步。

图17：DNA的表达

每种卵白量都有对应的DNA。

若是我们把卵白量视为产物，那么DNA就是设想图，卵白量是根据DNA造出来的[77][78][79][80][81][82][83]。好比我们运输氧气的血红卵白[84][85]就是生物操纵DNA编码出来的[86]，人体内无限多种的卵白量、酶、身体构造，都是如斯。

我们的每个细胞不竭凋亡，新的细胞不竭产生，那个产生过程，都是DNA表达的成果。我们也能够说，新陈代谢是依靠DNA来停止的，DNA是生命活动的中心。

图18：DNA——活动的中心四、训练：刺激DNA表达

我们在前面说了，我们的肌肉中的卵白量（肌动卵白/肌球卵白等）是大量氨基酸以特定体例摆列组合而成的。氨基酸的摆列组合，依靠mRNA；mRNA是DNA复造的产品。

所以，卵白量的“造造”过程，最次要是两部：DNA转录为mRNA，mRNA翻译为卵白量。

从DNA到卵白量，那也叫基因的表达。

那为什么DNA会起头转录？谜底是，有什么工具刺激了它。好比训练，一种施加在肌纤维上的机械外力，也叫机械张力。张，望文生义，把肌纤维往两边张开、拉开、扯开。

例如在哑铃弯举中，重力感化于哑铃，哑铃把肌纤维往下“扯”，我们本身的骨骼支持，把肌纤维往上拉，则构成了一个往两边张开的力。

图19：机械张力

机械张力为什么能刺激DNA表达[87][88][89]（转录）呢？因为我们有大量的生物感触感染器，能把外力信号，改变为细胞内的生物信号，那些信号不断传递到DNA上，刺激了DNA的转录，于是我们得到了肌细胞内的卵白量。

图20：机械刺激与细胞信号

肌肉上能感知机械张力的生物传感器有哪些呢？

例如肋节[90][91][92]，它将肌细胞膜与肌原纤维、细胞外基量毗连起来，加强肌细胞膜的不变性和强度，还能感触感染、侦测到施加于及细胞的外力（例如我们所说的机械张力），将其传导到肌细胞内部，转化为生物信号[16,17]；

71整合素[93][94]也是一种横跨细胞膜的受体，它一方面供给毗连感化[95]，一方面将机械信号从细胞别传递到细胞内。还有磷脂酸（PA）、FAK—粘着斑激酶等也参与机械张力转化为细胞信号的传导传导，就不多说了。

图21：生物传感器五、训练是若何刺激DNA表达的？谜底是细胞信号

生物感触感染器将细胞信号传递到细胞内，引发一系列细胞信号事务。此中最出名、最核心的细胞信号事务，也被称为PI3K/Akt/mTOR途径[96][97][98][99][100]。还有一些此外相对次要的途径（如ERK），碍于篇幅，我们就不在那里说了。

图22：增肌的核心—mTOR途径

mTOR是我们细胞内一种由2549个氨基酸构成的大卵白[101]，——它既是卵白量，也阐扬信号感化。

mTOR全称“哺乳动物雷帕霉素靶卵白”，是哺乳动物调理细胞生长、代谢、卵白量合成等关键心理过程中的重要卵白[102]。mTOR现实上以mTORC1（复合物1）和mTORC2（复合物2）的形式在人体内存在[103]。

图23：mTORC1

MTORC1次要通过S6K1和eIF4E的磷酸化，来引发DNA表达，促进卵白量合成[104]。此外，S6k1也进步mRNA的翻译效率[105]。

关于健身者来说，最典型的激活mTORC1的因素，当然是训练。

训练刺激（机械张力）可激活mTORC1，使其磷酸化[106][107][108][109][110][111]；在mTOR的下流，S6激酶[112][113][114]和eIF4E（实核生物起始因子4E）[115][116]随之也被磷酸化（红色方框）。

图24：机械张力传递到DNA，引发DNA表达

磷酸化是天然界一种十分遍及的、对卵白量停止化学润色的过程[117]。卵白量磷酸化有效地增加了其复杂性，远远超越了基因组所付与的多样性[118]。

在磷酸激酶的感化下，生物将磷酸基团加在卵白量或卵白类中间产品上，从而将卵白量磷酸化（或者去磷酸化）。经化学润色后的卵白量，功用/生物活性会显著差别。

目前已知的磷酸激酶多大500多种，可针对超越20000种卵白量上的25000个点位停止磷酸化[119][120][121][122]；磷酸化决定了在一般/病理形态下生物体对刺激的反响[123]。

S6k1是DNA转录因子[124]，名至实归。S6k1被激活后，接下来核糖体卵白6被磷酸化，从而增加了核糖体卵白与5‘端寡核苷酸(5’-top)mRNA的亲和力，引起了DNA转录[125][126][127]，增加卵白量合成[128][129][130][131]。

图25：S6k1

反过来，若是卵白量摄入不敷，氨基酸/原料不敷，则能够招致核糖体卵白6的“去磷酸化”[132]。已知的诱导卵白量去磷酸化的酶超越150种[119]。

研究发现，S6k它的磷酸化程度与增肌之间，存在极强的正相关性，r=0.998。下图纵轴是肌肉增加的幅度，横轴是s6k磷酸化程度，用俗话来说，它们几乎成反比。

图26：S6k磷酸化与增肌六、能激活mTOR途径的，不行有训练

市道上有一种典型的错误概念，认为训练才气增肌，好比下面图上的那种：

图27：错误概念

留意，图中有2个错误：

错误1：认为增肌的原理是损伤修复。那个错误我们在前面已经解析过了，增肌的次要原理是DNA表达而不是损伤。民间认为损伤增肌，次要是因为损伤是来自于训练，训练能激发DNA表达。

错误2：认为训练是增肌的前提。那也是错的，除了训练，营养[133][134][135][136][137][138][139][140][141]和激素也都能激发DNA表达，因为他们的分子途径是高度类似的，原理也不异：都是是通过刺激DNA的表达，来得到更多的肌卵白。

当然，它们的效果水平差别，那或许是因为三者招致的mTOR磷酸化水平纷歧样。

图28

我们肌肉中的卵白量就是那么来的：从激活细胞膜上的受体起头，一个个卵白/酶依次被激活，最初激活DNA转录，然后mRNA翻译为卵白量。

许多人很难承受“只打药不练就能够长肌肉”，若是他们晓得“只吃卵白粉不训练也能长肌肉”，估量就更无法承受了。但那是客不雅事实，不以他们的主不雅意志为转移。

Liu等人在《临床内排泄与代谢杂志》上颁发的了一项以10名安康年轻报酬对象的研究，对他们打针氨基酸，察看他们肌细胞内的变革（图30），灰柱“AA”是打针氨基酸后，白色是打针前。纵轴是磷酸化程度。

图30

氨基酸打针，招致p70S6K和eIF4E磷酸化，进而增加了核糖体卵白S6的磷酸化。S6被磷酸化后，促进了一些在卵白量合成中起重要感化的核糖体卵白的合成。

那些，也就证了然氨基酸打针或摄入能磷酸化4E-BP1、eIF4E、S6，进而引发卵白合成：换句话说，单纯的吃卵白量不运动，也会多几少长一些肌肉。

除了饮食/营养/训练三者，我们还列举了第四种刺激影响转录因子磷酸化的要素：光。

证据表白，光通过刺激SCN（视穿插上核）来影响ERK、或mTOR途径的下流因子S6核糖激酶的磷酸化。详细的，在我们之前的文章中有过论述。

保举阅读

肉崽：有哪些是你健身久了晓得的事？

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