For Slash reading: WHAT MAKES MUSCLES GROW?

Muscles.
We / have /over 600/ of them.

They make up /between 1/3 and 1/2 / of our body weight,/ and along with connective tissue, /they bind us together,/ hold us up,/ and help us move.//

And whether or not/ body building/ is your hobby,/ muscles need/ your constant attention / because/ the way/ you treat them/ on a daily basis/ determines/ whether they will wither/ or grow.// 

Say/ you're standing/ in front of a door,/ ready to pull it open.//
Your brain and muscles/ are perfectly/ poised/ to help/ you/ achieve this goal.// 

First,/ your brain/ sends/ a signal/ to motor/ neurons/ inside your arm.//
When they receive/ this message,/ they fire,/ causing muscles/ to contract and relax,/ which pull/ on the bones/ in your arm/ and generate/ the needed movement.// 

The bigger/ the challenge/ becomes,/ the bigger/ the brain's signal/ grows,/ and/ the more motor units/ it rallies/ to help you/ achieve your task.// 

But/ what if/ the door/ is made of/ solid iron?//
At this point,/ your arm muscles alone/ won't be able/ to generate/ enough tension/ to pull/ it open,/ so your brain/ appeals/ to other muscles/ for help.//
You plant your feet,/ tighten your belly,/ and tense your back,/ generating/ enough force/ to yank it open.// 

Your nervous system/ has just leveraged/ the resources/ you already have,/ other muscles,/ to meet the demand.//
While all this is happening,/ your muscle fibers/ undergo/ another kind of/ cellular change.// 

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

In response,/ the injured cells/ release/ inflammatory molecules/ called cytokines/ that activate/ the immune system/ to repair the injury.//
This is /when the muscle-building magic/ happens.//
The greater/ the damage/ to the muscle tissue,/ the more/ your body/ will need/ to repair itself.// 

The resulting cycle/ of damage/ and repair/ eventually/ makes/ muscles/ bigger and stronger/ as they /adapt/ to progressively greater demands.// 

Since our bodies/ have already adapted/ to most everyday activities,/ those generally/ don't produce/ enough stress/ to stimulate/ new muscle growth.// 
So,/ to build new muscle,/ a process/ called hypertrophy,/ our cells/ need/ to be exposed/ to higher workloads/ than they are used to.// 

In fact,/ if you don't continuously/ expose/ your muscles/ to some resistance,/ they will shrink,/ a process known/ as muscular atrophy.//
In contrast,/ exposing the muscle/ to a high-degree/ of tension,/ especially/ while the muscle/ is lengthening,/ also called/ an eccentric contraction,/ generates/ effective conditions/ for new growth.// 

However,/ muscles/ rely on/ more than/ just activity/ to grow.//
Without proper nutrition,/ hormones,/ and rest,/ your body/ would never/ be able/ to repair /damaged muscle fibers.//

Protein in our diet/ preserves muscle mass/ by providing/ the building blocks/ for new tissue/ in the form of/ amino acids.//

Adequate protein intake,/ along with naturally/ occurring hormones,/ like insulin-like/ growth factor/ and testosterone,/ help shift the body/ into a state/ where tissue/ is repaired and grown.//

This vital repair process/ mainly occurs/ when we're resting,/ especially at night/ while sleeping.//

Gender and age affect/ this repair mechanism,/ which is why young men/ with more testosterone/ have/ a leg up/ in the muscle building game.//
Genetic factors/ also play/ a role/ in one's ability/ to grow muscle.// 

Some people/ have more robust/ immune reactions/ to muscle damage,/ and are better able/ to repair/ and replace/ damaged/ muscle fibers,/ increasing/ their muscle-building potential.//

The body/ responds/ to the demands/ you place on it.//
If you/ tear your muscles up,/ eat right,/ rest and repeat,/ you'll create/ the conditions /to make your muscles/ as big and strong /as possible.//

It is with muscles/ as it is with life:/ Meaningful growth requires challenge and stress.//