7 August 2019

Solving the Hypertrophy Riddle – The Complexity of Muscle (PART 1)

by Jacob Schepis 0

    Even the word hypertrophy sounds elusive and mysterious. It’s undoubtedly one of the most widely misunderstood training goals. From what I can see, it is an objective that for many is also difficult to obtain.   Hypertrophy carries many of the same fictitious characteristics as a limited liability company. Large scale companies exist…



Even the word hypertrophy sounds elusive and mysterious. It’s undoubtedly one of the most widely misunderstood training goals. From what I can see, it is an objective that for many is also difficult to obtain.


Hypertrophy carries many of the same fictitious characteristics as a limited liability company. Large scale companies exist and operate without the lay person knowing who is responsible for handling complaints, who is in charge of quality control, where the functioning of a company even takes place or who is keeping the tens of thousands of staff it employs in line. Just as pinning down and truly elucidating responsibility in a limited liability company is a complicated and timely endeavor, understanding hypertrophy and writing an effective training program is equally enigmatic in its undertakings.


Just as many of the frameworks and constitutions of such organisations are hidden and protected behind complex legal documents and policy, hypertrophy brings about a similar paradox. The mechanisms of hypertrophy are far more complex than people imagine. Truth be told, I’m still unpacking the research and trying to fine tune and solidify my understanding of training and program design for hypertrophy.


While the majority of cognitive biases seek to save mental juice, complexity bias on the other hand is interesting because, at times, we make things harder than necessary. I definitely won’t argue for hypertrophy being a simple topic. I’ve been heavily invested in this domain for the better part of 3 years and still trying to crawl out of one of the hundreds of rabbit holes I’ve dug. However, I do think this may be the case for many folks who are merely interested in training to get more swole and have an interest in this area. They find any way they can to make matters unnecessarily confusing.


In this article I hope to deconstruct some of the intricate complexities of hypertrophy and hopefully exploit some otherwise unrecognized simplicities. This will be nothing more than my currentunderstanding of hypertrophy, program design and how I’ve come to make sense of the most hotly debated training variable over the past decade, volume.


The objective:bring you up to speed if you are still a little behind or confused about hypertrophy training and hopefully simplify this getting jacked thing as well as make my own thoughts on the matter a little more concrete.


A complex piece of machinery


A system contains a number of individual parts in order to operate. When there are a lot of similarities between multiple individual parts, they combine to form a collective. Each collective is a component of the larger system and when distinct enough, often times there are multiple systems within a system. All components and systems seek to operate harmoniously with other collectives to achieve the objective of the global system.


The more individual parts, components and systems there are, the more complex it can be said to be. When we zoom all the way out to observe a system in its entirety, things seem rather simple on the surface. However, we must appreciate that within it, combining all of the other systems, their individual parts and so on makes this one larger system all the more complex.


The more complexities within the system, often the less can be predicted from the surface. This is due to the sheer volume of individual parts, components and systems working beneath surface and all of which influence an outcome.


The human body and muscle growth is a prime example of this – we are one complex system comprised of multiple complex systems, such as the nervous system, respiratory system, digestive system and many others, including the musculoskeletal system. We’re made of about 100 trillion cells and yet we are so much more than the aggregation of our cells. You’d never predict what we’re like or who we are from looking at our cells.


Similarly, predicting muscle growth based on a single training session or after a few weeks of following a program is near impossible given the vast amount of systems and factors that influence how muscle grows.


Let’s unpack this a little further…


A Primer on Muscle 


For a more detailed and in-depth assessment of the following primer on muscle, I suggest you read Lyle McDonalds three-part series HEREHEREand HERE. This is simply a reiteration of what I’ve read a million times over in text books and articles and hopefully a much more simplified version of that. If you aren’t interested in reading Lyle’s long winded ramblings and prefer a more concise recollection, read on.


Muscle cells are an individual component within the musculoskeletal system. Each skeletal muscle consists of a bundle of cylindrical fibers (myofibrils), and each fiber contains mitochondria, nuclei, sarcomeres and a sarcoplasmic reticulum. The anatomy and structure of a muscle determines its function at a physiological level, which is why skeletal muscle functions differently to smooth and cardiac muscle tissue.


Skeletal muscle requires an impulse from the nervous system in order to contract. The nervous system sends a signal down the spinal cord to a motor unit that innervates the fiber it is connected to. Once this signal is received, a cascade of processes unfolds that lead to the muscle fibers shortening (sliding filament theory) in order to meet the imposed force demands. The bones move, and the activity performed – i.e. the weight is lifted and gravity defied.


The force demands will determine which types of fibers are called upon, with type II (fast twitch) fibers being recruited for activities that require high degrees of force and type I (slow twitch) fibers utilised for lower force outputs or activities that require more oxygen such as aerobic exercises. As it relates to hypertrophy, it is the type II fibers which have the greatest potential for growth.


Fibers are recruited from smallest to largest in order to meet and sustain force demands (Hennemans size principle). High force exercise recruits type II fibers from the onset, and in activities that see fatigue rise beyond the capabilities of type I fibers, that is they can no longer meet the force demands, type II fibers are called upon to help out.

When a muscle produces significant amounts of force during contraction(s) coupled with a slow velocity of contraction (such as under fatigued conditions), this in turn leads to high degrees of mechanical tension being generated by the muscle. This mechanical tension plays a pivotal role in the processes that follow.



  • Muscle tissue is a component of a larger, more complex system
  • Complex and multi-component systems, within a system, makes predicting surface level outcomes, such as muscle growth, difficult.
  • Skeletal muscle contracts due to nervous system impulse
  • Activities which require high force demands recruit type II fibers
  • Type II fibers have the greatest potential for growth
  • High force production creates high amounts of mechanical tension at the muscle fiber level.



How Muscle Grows


It is fairly well established that muscle growth occurs in response to mechanical tension. This mechanical signal is converted into a chemical signal via mechanoreceptors which then triggers a key pathway for muscle growth – mTOR.


Once activated, mTOR alters myofibrillar protein turnover in favour of synthesis aka building new proteins and voila, muscle building begins. As it stands, metabolic stress and muscle damage play a secondary and additional role to muscle growth, but it’s tension that is the primary mechanism of hypertrophy.


Therefore, to create the mechanical tension required to turn on this muscle building process, we need:


  1. High force outputs to recruit high threshold motor units (type II fibers);
  2. Slow velocity contractions
  3. To expose the muscle to the above for some number of contractions/repetitions.


Thus, training for hypertrophy should seek to satisfy the aforementioned requirements. The means by which we do this is three-fold. Simply put, training for muscle growth necessitates:


  1. Lifting heavy (absolute loads above 40% of 1RM);
  2. Lifting hard (close proximity to failure – RPE of >5 OR RIR of <5).
  3. Lifting enough (volume – exposure to tension).


The absolute load and proximity to failure are the intensity thresholds that need to be met to elicit a sufficient mechanical tension. Exposure to that tension comes in the form of volume, which can be measured by the number of hard working sets per week per muscle group or the number of effective /strongly hypertrophic repetitions per muscle group, per week.

The recommended guidelines are as follows:


  1. Train with loads 40-85% of 1RM;
  2. Train with relative intensities of RPE ~7;
  3. Train with 10-20 sets per week, per muscle group
  4. Train each muscle group ~2-3x per week.


The distinction between number of hard sets and ‘effective reps’ is important as the latter more accurately describes exposure to tension. Thus intensity and volume are critical variables in program design, and will be the focal point for the subsequent part of this article.


The exact amount of volume or exposure to the tension stimulus is where much debate lies, and is a question that is yet to be answered given the marked variation in individual response to training. More on this later…


Nonetheless, once a muscle is exposed to a potent stimulus for growth (a sufficient number of repetitions that elicit a high magnitude of tension) it will grow. Provided this stimulus is yielding an effect that leads to positive protein turnover of course. When growth occurs, the cross sectional area of the muscle increases, meaning it can produce more force relative to its size. This necessitates an increase in load to maintain the same or greater force demands to satisfy intensity thresholds (progressive overload).


For example, performing 3×8 with 100kg for an RPE of 7 may be sufficient to initiate a growth response. Over time, as muscle growth occurs, load will need to be added to the bar. If the CSA of a muscle increases, 3×8 with 100kg will eventually fall below the intensity threshold necessary to elicit a growth response. For example, if the 3×8 with 100kg can be performed for an RPE of <5, it’s not doing much for growth.


Adding weight to the bar is likely the best proxy for long term muscle growth in an applied sense and relative intensity our best guess at assessing mechanical tension. Although having such parameters in place is fundamental, so too is a lifters understanding and use of  RPE/RIR scales – ensuring they meet intensity thresholds.

Simply put, lifters need to accurately assess their effort via RPE/RIR and if you’re doing things right, you will be growing. Thus, you should be lifting more weight over time – all else being equal.



  • The primary mechanism of muscle growth is mechanical tension
  • Mechanical tension can be achieved via high force outputs with slow contraction velocities
  • A sufficient number of contractions is required to provide a growth signal
  • Lifting heavy, hard and enough via intensity and volume prescription is how sufficient tension stimulus is obtained
  • As growth occurs, a muscle can produce more force relative to its size, which means greater loads can be lifted or the same load lifted with less effort.


Stay tuned for Part 2 of this series as I explore training volume further and hope to refine and better conceptualise the concept of training volume, it’s relationship with intensity and frequency and how what is an optimal stimulus may vary different time points of a lifters career and how this can be achieved through the acute training variables.


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