How Does the Muscle Grow? Here's how hypertrophy really works

How does the muscle grow?

The human body literally has a full-on, adaptive biosuit. Isn’t it amazing?

If you look at some of the best physiques, they look borderline extraterrestrial.

But…

What triggers muscle growth?

Well, the mechanism is simple – Subjecting the musculature to progressively increasing stress, causes disruptions in the muscle fibers.

That in turn sets off a chain of events that lead to an increase in the amount and size of the muscle fibers and their sarcoplasm (the jelly-like fluid surrounding the fibers)

Muscle growth (hypertrophy) is just how the body adapts to stress from resistance, so that it can endure more of that stress, for longer.

This is also referred to as an “Adaptation”.

Now, to understand more about the muscle and how it works, let’s first break it down.

Types of muscle fibers

how does the muscles grow - muscle fibers

There are two main types and two sub-types of muscle fibers.


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The two main ones are Type 1 slow-twitch muscle fibers and Type 2 fast-twitch muscle fibers.

Type 1 Slow twitch muscle fibers

These are fibers that have an abundant supply of blood, but have low contractile speed.

The slow twitch fibers are designed for extensive work.

If you followed the logic of the last few articles from the series, you would now know that these fibers are supplied aerobically – Aerobic work = Extensive work.

These muscle fibers are smaller and weaker, as opposed to the fast-twitch muscle fibers.

Type 2 Fast-twitch muscle fibers

These muscle fibers have lower blood supply and a high speed of contraction.

The type 2 fast-twitch muscle fibers are bigger, more powerful and specifically designed for explosive work.

Fast-twitch fibers can work in both anaerobic and aerobic conditions and have the most hypertrophy (growth) potential.

There are two more subtypes to this second type of muscle fibers.

Type 2 A and Type 2 B muscle fibers

The type 2 A fibers are also known as intermediate fast-twitch fibers.

They can use both anaerobic and anaerobic system to fulfill the energy demand.

To some degree, Type 2-A fibers are a mix of Type 1 and Type 2 fibers.

On the flipside, type 2-B fibers are entirely anaerobic.

They are referred to as “immediate muscle fibers”.

That is simply because they were made to produce quick bursts of power.

As we learned though, quick bursts are not sustainable.

Which means that even though these fibers have the quickest contractile speed, they also reach fatigue quicker.

So, let’s check this table that sums it all up.

muscle fiber types

So far, so good. We’re starting to understand more about how our body works.

Muscle unit activation

One motor unit is a nerve, plus the muscle fibers attached to it.

Each and every muscle group has a certain ratio of both types of muscle fibers (Fast and slow-twitch)

As we learned, Type 1 motor units are easily engaged and are also more resistant to fatigue.

On the other hand, we also learned that Type 2 motor units are bigger, stronger and less resistant to fatigue.

We can mention here that when there’s a demand for a muscle to be contracted, the body optimizes the process, by first activating the type-1 Muscle fibers

As the demand grows and more force needs to be produced, the central nervous system engages the stronger, type-2 muscle fibers.

That’s exactly why the growth in intensity is required for optimal muscle gains.

100% activation

muscle fiber activation

Alright, we made clear that we only observe partial activation of muscle fibers at lower levels of intensity (30-50%).

It is important to understand that 100% activation is not observed at 100% intensity (one rep max), but rather at around 70-85%.

So, if you have a one rep max of 100 kg on the bench press, 100% of your chest, triceps and shoulders will be activated at around 80 kg.

Further increases in intensity are only possible via an increased frequency of the brain to muscle signals.

In otherwords, when you’re using a powerlifting approach in your training, you will mostly develop the nerve paths leading to the muscles, as well as the muscle fibers.

However, with that type of training, bulk muscle growth is a secondary adaptation.

That is exactly why bodybuilders just lay a foundation of strength with powerlifting, then focus on training splits that include quality volume with more density.

This leads us to the next point.

Types of muscle growth

types of hypertrophy

There are two types of muscle growth – Myofibril hypertrophy and Sarcoplasmic hypertrophy.

Myofibril hypertrophy

This is often referred to as “functional hypertrophy”, simply because this is the growth of the contractile elements of the muscle – The muscle fibers.

Needless to say, the muscle fiber play an essential role in muscle contraction.

With myofibril growth (hypertrophy) we mainly observe an increase in strength.

Athletes such as strongmen and powerlifters seek this type of development.

Sarcoplasmic hypertrophy

The sarcoplasm is the jelly-like fluid that surrounds the muscle fibers.

It contains non-contractile, energy elements like water and protein.

This is often referred to as “Energetic hypertrophy”.

This type of growth results in a more pronounced, bulky, lean and separated bodybuilder-type musculature.

Sarcoplasmic hypertrophy allows you to complete a bigger workload.

The strength gains with sarcoplasmic hypertrophy however, are secondary.

This is the most sought type of growth amongst bodybuilders and physique athletes.

Bottom line

Muscle growth, otherwise known as hypertrophy, is an adaptive reaction of the organism.

It occurs when we subject our bodies to previously unknown stress.

When we do so, the body has two options –

  1. Increase the size of the contractile elements (Muscle fibers). This primarily results in an increase of strength
  2. Increase the energy stores, so that a bigger volume can be completed. This primarily results in an increased muscle bulk and less strength gains.

Needless to say, the type of hypertrophy that will occur with our training, strictly depends on the parameters that we express in the workout.

And so, let’s take an example of training in the 3-5 rep range.

That would mean we’re doing high-intensity work, using the Anaerobic-Alactic (Immediate) energy system and also stimulating myofibril hypertrophy.

By now, you should get the idea and make sense out of the past 3 articles.

For the next article, we’ll talk about something that is borderline taboo – Cardio.

If you feel like you don’t want to do cardio because it’s going to kill your gains, then our next article will be perfect for you!

Stay tuned.

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