We have over 600 of them.

超過六百個肌肉在我們身體內部

They make up between 1/3 and 1/2 of our body weight,

肌肉和組織占了我們體重的三分之一到二分之一

and along with connective tissue,

藉著結締組織

they bind us together, hold us up, and help us move.

肌肉把我們的身體構成一體，幫助我們移動

And whether or not body building is your hobby,

不管你習不習慣健身

muscles need your constant attention

你得不時地注意你的肌肉

because the way you treat them on a daily basis determines whether they will wither or grow.

因為你每天如何運用你的肌肉，決定了你的肌肉會萎縮還是成長

Say you're standing in front of a door, ready to pull it open.

當你站在門前要拉開門

Your brain and muscles are perfectly poised to help you achieve this goal.

你的大腦和肌肉會保持平衡，來協助你達成目標

First, your brain sends a signal to motor neurons inside your arm.

第一，大腦會發送訊息到手臂的運動神經元

When they receive this message, they fire,

當神經元接收到訊息，便會活躍起來

causing muscles to contract and relax,

讓肌肉收縮或放鬆

which pull on the bones in your arm and generate the needed movement.

拉持臂膀的骨頭，以便產生所需要的移動

The bigger the challenge becomes, the bigger the brain's signal grows,

隨著挑戰性的增加，大腦訊息也跟著增強

and the more motor units it rallies to help you achieve your task.

也有更多的運動神經元聯合起來，協助你達成任務

But what if the door is made of solid iron?

那如果這扇們是鐵做的呢?

At this point, your arm muscles alone won't be able to generate enough tension to pull it open,

這樣的話，單靠你臂膀的肌肉是不足以產生足夠的力道將門打開的

so your brain appeals to other muscles for help.

所以你的大腦向其他部位的肌肉求助

You plant your feet, tighten your belly, and tense your back,

於是，你站穩腳步、縮小腹，然後躬起身子

generating enough force to yank it open.

產生足夠的力氣將門拉開

Your nervous system has just leveraged the resources you already have, other muscles, to meet the demand.

你的神經系統利用槓桿原理，將你身體原有的資源和其他肌肉結合起來達到目的

While all this is happening,

事情發生的當下

your muscle fibers undergo another kind of cellular change.

肌肉的纖維產生了細胞變化

As you expose them to stress, they experience microscopic damage, which, in this context, is a good thing.

當肌肉受到外力時，會有顯微的損害，在這樣的情況下，反而是件好事

In response, the injured cells release inflammatory molecules called cytokines

相對地，受傷的細胞釋放出發炎的分子，稱為細胞因子

that activate the immune system to repair the injury.

促使免疫系統修復損害的地方

This is when the muscle-building magic happens.

這時肌肉增長的魔力發生了

The greater the damage to the muscle tissue,

肌肉組織的損害越大

the more your body will need to repair itself.

身體自我修復的需求也越多

The resulting cycle of damage and repair

損害與修復一再地循環

eventually makes muscles bigger and stronger

最終讓肌肉變得更大、更強壯

as they adapt to progressively greater demands.

如此能夠適應所需的肌力

Since our bodies have already adapted to most everyday activities,

因為我們身體早已適應每天多數的活動

those generally don't produce enough stress to stimulate new muscle growth.

基本上不會有足夠的壓力來刺激新肌肉的成長

So, to build new muscle, a process called hypertrophy,

肌肉成長的過程，稱為「肌肉機能發達」

our cells need to be exposed to higher workloads than they are used to.

相較於一般情況下，細胞需要更多的負荷量

In fact, if you don't continuously expose your muscles to some resistance,

如果你沒有讓肌肉持續地承受肌耐力

they will shrink,

肌肉則會萎縮

a process known as muscular atrophy.

我們稱之為「肌肉萎縮」

In contrast, exposing the muscle to a high-degree of tension,

相對地，讓肌肉承受高單位的張力

especially while the muscle is lengthening,

尤其是肌肉伸張時

also called an eccentric contraction,

我們稱為「離心收縮」

generates effective conditions for new growth.

讓肌肉有效地成長

However, muscles rely on more than just activity to grow.

然而，肌肉的成長不僅僅依賴日常的活動

Without proper nutrition, hormones, and rest,

沒有該有的營養，賀爾蒙的分泌和適當的休息

your body would never be able to repair damaged muscle fibers.

你的身體將無法修復受損的肌肉纖維

Protein in our diet preserves muscle mass

飲食中的蛋白質能保存肌肉群

by providing the building blocks for new tissue in the form of amino acids.

提供新組織增長所需的胺基酸

Adequate protein intake, along with naturally occurring hormones,

攝取足夠的蛋白質，加上自然分泌的賀爾蒙

like insulin-like growth factor and testosterone,

例如胰島素和睪酮

help shift the body into a state where tissue is repaired and grown.

能幫助身體的細胞修復和成長

This vital repair process mainly occurs when we're resting,

當我們休息時，是細胞修復最重要的時間

especially at night while sleeping.

特別是晚間睡眠時

Gender and age affect this repair mechanism,

性別與年齡也影響了修復的機制

which is why young men with more testosterone

年輕的男性，因為有較多的睪酮

have a leg up in the muscle building game.

所以肌肉的成長也比較快

Genetic factors also play a role in one's ability to grow muscle.

基因在每人肌肉成長，也扮演了重要的角色

Some people have more robust immune reactions to muscle damage,

對於肌肉的損害，有些人免疫系統的反應比較強健

and are better able to repair and replace damaged muscle fibers,

肌肉纖維受損後的修復、代謝比較好

increasing their muscle-building potential.

增加了肌肉成長的潛力

The body responds to the demands you place on it.

你的身體會呼應你的需求

If you tear your muscles up, eat right, rest and repeat,

讓你的肌肉細胞分裂、吃對的食物、適當休息，並且循序漸進

you'll create the conditions to make your muscles as big and strong as possible.

你就能賦予你肌肉，長得又大又壯的條件

It is with muscles as it is with life:

肌肉之於人生，人生之於肌肉

Meaningful growth requires challenge and stress.

面對挑戰與壓力，成長才有意義