Defining Muscle Growth

by DeanMcKillop 3552 views Gain Muscle

Defining Muscle Growth

Almost every week I see an article pop up on Facebook, in an email or on a popular website listing the top 5 ways to ‘get jacked’ or ‘How to gain 10lbs in 10 weeks’... but what do they actually mean?

What does getting jacked actually mean?

None of these articles ever really discuss muscle growth itself but instead just tell you how to grow it.

What is muscle growth?
  • Are their different types of muscle growth?
  • Can we stimulate different pathways of growth?
  • Can we grow new tissue or just make current tissue bigger?

Well, for once we are going to get into the nitty gritty of muscle growth, define what muscle growth actually is and briefly discuss how we can actually achieve muscle growth through varying training methodologies.

First let's discuss the two proposed theories of muscle growth:

An increase in muscle fibre size
An increase in muscle fibre quantity

For years it has been debated on whether hyperplasia is possible after prenatal fibre distribution occurs (meaning the amount of fibres you get as a baby is all you ever have). Should this theory be possible, humans would, in essence, be able to not only grow bigger existing tissue but also increase the number of actual muscle fibres as well.


Most commonly, the primary reason for muscle growth and an increase in muscular cross-sectional area post resistance training is attributed to myofibrillar hypertrophy (1). And despite there being some research now indicating that myofibrillar hyperplasia may be possible (mainly in animals, yet to be proven in humans), the methods used to achieve hyperplasia, in essence, are similar to standardised hypertrophy programming anyway.

So for this article, I will be working on the fact that Hyperplasia does not need to be focused on given that primary growth still comes from hypertrophy (1)(2) and even if hyperplasia was possible, the stimulatory nature of standardised hypertrophy training would essentially achieve both theories of muscle growth anyway. 

So whether we can increase fibre size or quantity isn’t really all that important, especially considering the research for hyperplasia is still quite limited and the primary proven method for muscle growth is hypertrophy.

So let's focus on hypertrophy.

The two types of muscle hypertrophy are:


Which is an increase in actin and myosin size, which causes an increase in myofibrillar thickness. This can be thought of as being actual muscle tissue growth.


Which is an increase in intramuscular content storage, of which primarily comes from the increase in intramuscular glycogen and accompanying water.

So in a nutshell, myofibrillar hypertrophy refers to the increase in actual mechanical tissue size, which provides functional benefits such as performance enhancement, whereas sarcoplasmic hypertrophy is primarily responsible for an aesthetic gain (how you look) without any mechanical tissue advantage other than an increase in muscle cross-sectional area, which may aid in improving strength for some individuals although is only minor in comparison to myofibrillar growth.

Now to the fun part… how do we maximise Myofibrillar Hypertrophy while maintaining an optimal sarcoplasmic environment for complete muscle growth?

Training Methodology

First and foremost we must understand that myofibrillar hypertrophy occurs as a result of mechanical stress, of which research indicates that the primary training methodologies to improve this in order are:

  1. Volume, Intensity, Frequency
  2. Progression
  3. Exercise Selection
  4. Rest Periods
  5. Tempo

*Courtesy of the Eric Helms Muscle and Strength Training Pyramid


Focusing primarily on point number 1 as these are the 3 primary determinants for eliciting a hypertrophy response, we can either choose to work on increasing volume (total sets, reps or total weight lifted for the session), the intensity can go up whereby you are training at a higher percentage of your 1RM or you can increase the frequency of stimulating the target muscle more often during the week or month. 

We cannot, however, attempt to maximise all 3 modalities at once, as this will result in an increased risk of injury, training regression and a decrease in results. And whether you choose to focus on volume, intensity or frequency, it is of primary importance to focus on progression.

This is why I am a big promoter of programming all athletes and clients of mine as it gives me a measurable indication of performance, which can then be extrapolated against each clients nutrition to determine if we are in a positive environment for either muscle gain or muscle retention during a fat loss phase.

If it's measurable and we can lift more, lift heavier or lift more frequently, essentially we are stimulating the muscle to grow larger in order to keep up with the workload we are placing it under. If training is not measurable, then we essentially have no means of determining whether or not the weight gain is a result of muscle growth or simply just weight gain from glycogen, water and fat.

Hands down for me, measurable training progression through volume, intensity, frequency and progression measurement is the best indicator of what you can expect physically from your training and nutrition program.

So what about Sarcoplasmic?

Well, while sarcoplasmic hypertrophy is still a viable way of increasing muscle size and therefore the look of a physique, my personal experience is that focusing on this type of muscle growth results in a much faster decline in apparent muscle size lost in those who decrease training versus those who have grown bigger tissue.

Sarcoplasmic hypertrophy is primarily determined by the dietary ingestion of carbohydrates and water, as well as intramuscular inflammation from intense metabolic sessions such as high rep ‘pump’ training. For me, this is a ‘superficial’ aesthetic gain that only lasts while stimulation remains high, but is quickly lost if exercise is reduced.

In a nutshell. Those who focus primarily on the pump and sarcoplasmic hypertrophy, look smaller faster during a reduction of training volume or frequency when compared to those who have grown large tissue (as opposed to content) as a result of myofibrillar growth.

Focusing on sarcoplasmic hypertrophy certainly has its place in a training session by focusing on metabolically demanding training such as drop sets, supersets, giant sets, rest pause sets and high rep sets, however should only ever be a tool within a program focused on strength and volume progression as opposed to being the primary training methodology used.

Final Notes

Muscle growth occurs due to the increase in myofibrillar size, intramuscular sarcoplasmic content storage and potentially even an increase in muscle fibre quantity.

Regardless of the type of training methodology you prefer, in order for genuine muscle tissue growth to occur, a program focusing primarily on the progression of weight training volume, intensity or frequency should be paramount. While ‘pump’ sets have their place in a program for stimulating metabolic stress without as much mechanical load (which may reduce the risk of injury) it should only be used as a tool within the program as opposed to it being the primary focus.

A muscle that is forced to be stronger is forced to be bigger!

Train smart.

Li, M. et al. (2015). Not all the number of skeletal muscle fibers is determined prenatally. DMC Developmental Biology. 15(42).

Li, M. et al. (2015). Not all the number of skeletal muscle fibers is determined prenatally. DMC Developmental Biology. 15(42).


Exercise Scientist

I completed my Exercise Science Degree at the University of QLD and have worked in the fitness industry for over 8 years, including a short stint at the Brisbane Broncos in 2010 as a student. I also hold my Level 2 Strength and Conditioning Coach accreditation (ASCA) and have competed in 1 bodybuilding season, placing 2nd at the IFBB u85kg Nationals.

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