How Muscles Grow: The Science and Facts Behind Muscle Hypertrophy

If you’re moving heavy weights in the gym, you’re probably not just there to burn off some unwanted fat. You’re probably also trying to build some solid muscle.

If that’s your goal, knowing the science is crucial.

The science behind bigger muscles – find out how to increase your muscle mass the right way

This article will cover the science and mechanisms involved in muscle growth. It’ll also touch on female muscle growth and why women can have a hard time putting on big gains with weights.

There are three distinct types of muscles.

Cardiac muscles are responsible for moving your heart.

Smooth muscles make up the supporting tissue for internal organs. The third type, skeletal muscles, are muscles that move bones and other structures in your body. We’ll focus on skeletal muscles for the purpose of this article, as these are the muscles engaged when you lift weights.

Skeletal muscles are made up of muscle fibers, and muscle fibers are made up of tiny thread-like structures call myofibrils and sarcomeres. Imbedded between these tiny threads are even tinier clusters of motor neurons.

These motor neurons are connected to the outer portion of muscle fibers (the sarcoplasmic reticulum) and cause muscles to contract through electrical impulses sent from the brain. Training the activation of motor neurons—and therefor the contraction of muscles—is essential to getting stronger. This training process is called “motor unit recruitment”.

High motor unit recruitment is the reason small powerlifters can often lift heavier weights than much larger bodybuilders. The powerlifters’ muscles might look smaller, but their motor neuron activation has been better trained.

Motor unit recruitment is also the reason certain movements become easier to perform over time (muscle memory) and why most strength gain happens when you first start weight training. As you begin training, motor neuron activation is primal and raw.

Over time and with practice, this activation becomes more refined and your body gets used to the activity.


Anatomy and Physiology—Inside Your Muscles

Your muscle fibers are damaged when you lift weights. The strain causes tears in the fibers’ structure. While you’re resting, your body repairs damaged muscle fibers by using protein to fuse fibers together. This process is called protein synthesis.

What’s inside the muscles

This increases the ‘strength’ and durability of the fibers by increasing fiber thickness. These new, fused strands are called myofibrils. This process is what you notice when you see muscles getting bigger.

Muscle hypertrophy (growth) occurs when more protein synthesis is happening than protein breakdown. It’s important to remember: protein synthesis only happens when you rest, not while you’re working out. More on that later.

Okay so… how do you add muscle? Well, you should ask “satellite cells”. Satellite cells enter your muscle cells during protein synthesis. They adapt themselves to function exactly like muscle cell nuclei, in effect giving you more muscle cells.

So, the more protein synthesis occurs, the more satellite cells reach your muscles to become more muscle cells, and the more muscle you can then flex in your bathroom mirror. Looking good!

There’s some science to indicate that some people (“genetic freaks”) might naturally have higher satellite cell activation than people who have a hard time gaining muscle.

Some research has even shown that “extreme gainers” could push 58% myofiber hypertrophy with a whopping 23% activation of satellite cells.

To put that in perspective: average rates were 28% muscle growth and 19% satellite cell activation. It’s clear that satellite cell activation can make a huge difference. So how can we use this knowledge to our advantage? Is there a way to activate satellite cells at a higher rate and promote muscle growth?

The 3 Reasons Muscles Grow

Stress, stress, and stress. No, those aren’t the real three reasons, but they might as well be. Putting stress on your muscles (i.e.: lifting weight, running, etc) disrupts your body’s natural baseline (homeostasis). The act of stressing your muscles and then allowing them to react to that stress cause three key mechanisms to activate muscle growth.

1. Tension

To put it simply: lift heavier weights. To encourage your muscles to grow, you need to apply loads of stress (weight) greater than what your body is used to. When you give your body something new to adapt to, homeostasis is broken and the body will activate processes that help bring it to a new homeostasis in its new environment.

Increase your weights gradually

Lifting gradually heavier weights encourages protein synthesis, drawing in more satellite cells. This method also strengthens the grip connection your motor neurons have with your muscle cells, which increases overall performance.

2. Damage

As mentioned before, your muscle fibers are damaged each time you work out. You might often feel this as soreness or muscle fatigue. Soreness is created by your body’s release of various immune system cells that call upon satellite cells to fill the fatigued space.

Do harder workouts

Harder workouts will cause more damage and produce more satellite cell activation. Thus, more soreness. This occurs each time you work out and, over time, you might not feel as sore as you were originally. That’s okay. You’ll get used to soreness after a time thanks to other mechanisms associated with a healthy workout routine.

3. Metabolic Stress

Part of your body repairing muscular damage is ‘metabolic stress’. This occurs with cellular swelling around a damaged muscle or muscle fiber. This swelling comes from muscle glycogen (essentially, muscle fuel) being flooded into damaged or fatigued areas.

This swelling might make it appear as though your muscles have increased in size, but the swelling is temporary and does not indicate any higher levels of strength. This post-workout “pump” is called sarcoplasmic hypertrophy.

Those are the mechanics, but what about the chemistry? After all, what good is an engine without gasoline? Enter hormones.

Hormones’ Influence on Muscle Growth

Blanket statement: your endocrine (hormone) system runs everything. It’s the boss of all your bodily processes. So it’s no surprise that it’s a major contributor for muscular growth. Specifically, hormones play a huge roll in satellite cell activation. The big hormone to watch out for here is testosterone.

Testosterone is the hormone everyone names when they talk about hormones and muscle growth. And everyone just might be onto something there. There’s science to indicate that testosterone encourages protein synthesis, reduces protein breakdown, activates satellite cells, and stimulates other hormones and hormone processes.

A huge portion of testosterone in the body, about 98%, is locked into other processes and can’t be used. But, strength training appears to release more testosterone throughout the body. Strength training also appears to make muscle cells more sensitive to accepting testosterone in the future.

The Insulin Growth Factor (IGF) is another mechanism of the endocrine system that assists in muscle growth. The IGF oversees muscle hypertrophy through spiking protein synthesis, increasing the uptake of glucose, sending more amino acids into the skeletal muscles, and encouraging satellite cell activation. (There are those helpful satellite cells again!)

But even knowing all this stuff, you can’t just spend all your time in the gym and double your size. Your muscles need rest.

The Importance of Rest in Muscle Growth

Your body and your muscles use food stores to power all of its important processes. And these food stores are… well, in your body. Every engine will break down if you run it for too long without giving the parts some time to rest, and every engine needs fuel.

Without proper rest and nutrition, your body will eat through its regular fuel stores and enter a catabolic state. While your body is catabolic, it’s eating things it shouldn’t be eating in order to survive. Proper rest and nutrition allow your body to correctly prioritize the fuel it’s using at any given time.

That said, even if you eat and rest and exercise with great care, there are limits to how much your muscles can grow. Age, gender, and genetics all play factors. For example, women will have more difficulty gaining muscle mass simply because their bodies usually hold less testosterone.

What To Expect Over Time

Healthy muscular hypertrophy takes time and can be aggravatingly slow. Your nervous system will need some time to get used to activating motor neurons and building thicker myofribils.

It can be weeks or even months before results are clearly seen. Genetics also play a huge factor here. What’s important is to keep protein synthesis rates above protein breakdown rates. It really is as simple as that.

Consume adequate proteins and carbohydrates to build glycogen stores so that your muscles have all the fuel they need to make repairs. As long as you’re dedicated, you will see results eventually.

My final thoughts on muscle growth

Instigate muscular growth by creating stress and breaking your body’s homeostasis. This is easiest by lifting gradually heavier weights. Change up your exercise routine often. Eat well and with performance in mind so your muscles have adequate fuel.

Most importantly, give your body time to rest! Do all of this with care and you’ll be rippling in no time!

Now go lift something.

Gasper Novak

I train hard (lift weights + cardio) and try to eat right!

I enjoy reading about improving my physique and write about muscle building, shredding fat and supplements that give you that little edge over your competitors.

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