Jaquish Biomedical
April 6, 2021

How Does Muscle Hypertrophy Work?

A man flexes his back muscles after strength training
Flexing After Muscle Hypertrophy Training

Ever wonder how muscle hypertrophy, or the increase and growth of muscle cells, actually works? What types of training are most effective for hypertrophy?

What exactly is growing under that skin in your bicep peak?

Look no further, as we’ll discuss the different types of hypertrophy, the principles behind muscle growth, and the most effective methods for building size.

What Are The Types of Muscle Hypertrophy? #

There are two types of hypertrophy: myofibril hypertrophy and sarcoplasmic hypertrophy.

Myofibril hypertrophy refers to increasing the power output capacity of myofibrils—thin contractile elements bundled together to make a muscle fiber. Heavy, low-volume strength training promotes the growth of new sarcomeres, the mechanical contractile units within myofibrils, which are composed of protein filaments.

Myofibril hypertrophy is directly correlated with increasing the amount of peak force a muscle can produce.

Sarcoplasmic hypertrophy refers to increasing the sarcoplasm’s volume (the cytoplasm, or fluid, of a muscle cell) surrounding the myofibrils. Lighter, high-volume strength training causes the muscle to swell with blood, carrying hormones and metabolites that help the muscle adapt to longer workout periods in the future (think of THE PUMP).

Sarcoplasmic hypertrophy is predominantly associated with increases in muscular size.

What Are The Principles Behind Hypertrophy? #

Several factors 1 influence mechanical loading, and therefore hypertrophy. We’ll focus on the size principle and the force-velocity relationship.

Let’s dive a bit deeper into each of these.

The Size Principle #

The size principle states that motor units (a motor neuron and the fibers it controls) are recruited in order of size. To create a small amount of force, only smaller, low-threshold motor units are recruited, whereas creating a large number of force targets both small and large motor units, and therefore more muscle fibers. The muscle fibers of large motor units are more responsive to hypertrophy, so training should aim to create high levels of force that target the large, high-threshold motor units and fibers that are more likely to grow.

The Force-Velocity Relationship #

The force-velocity relationship is simple: muscles can produce more force when shortening slowly than when they shorten quickly. This is because there is more time for cross-bridges to form, the mechanism that allows the myofibrils to pull on each other and shorten the muscle.

This allows those large, high-threshold motor units to fire more muscle fibers, leading to increased size.

What are the Best Training Methods for Hypertrophy? #

John Jaquish performs a bicep curl outside with X3
Outdoor X3 Bar Bicep Curl

There are many methods to train for getting bigger. Ask ten people, and you’ll likely get ten different answers. However, some may be better than others based on time, complexity, and equipment.

So, what is the best way to train for hypertrophy?

Traditional bodybuilding movements like bicep curls and bench presses can lead to hypertrophy.

However, despite their frequent use, they are not well optimized as the load used for such exercises is limited by the weakest part of the movement, such as the bottom of a bench press.

A more effective workout technique would avoid this limitation using variable resistance to provide lower forces in the weakest part of the movement and higher forces in the strongest portion.

One study 2 investigating this concept found that groups using a variable resistance cam system that better matched the strength curve of the elbow flexors (primarily the biceps) had a more significant improvement in muscle torque than a group using a disc cam, which applies the same tension throughout like a typical barbell movement.

In fact, only the groups using the variable resistance cam had increases in hypertrophy after the 8-week training program. Without variable resistance, study participants got no measurable hypertrophy results after 8 weeks of training, indicating a serious deficiency in conventional fixed resistance training methods.

Hormonal impacts are also important to hypertrophy results. A study 3 on hormonal responses to different exercises found greater testosterone and growth hormone levels after a back squat than a leg press.

Findings like this were summarized in a recent meta-analysis 4 finding that self stabilized movements, like those undertaken with free weights, activate reflexive muscle stabilization not seen with machine-based movements, and this reflexive activation seems to cause a greater hormonal response and, therefore, greater strength and more hypertrophy.

A New Way to Look at Things #

Although we can combine multiple exercises to properly load the stronger portion of a movement, like a reverse band or partial range bench press, it’s not time efficient.

Furthermore, as one uses heavier free weights, the risk of injury increases significantly, and the repetition count drops off steeply, minimizing the stimulus for sarcoplasmic hypertrophy.

So, how can we target the most muscle throughout an entire movement and optimize myofibril and sarcoplasmic hypertrophy?

By using a powerful variable resistance device, such as the X3 system.

The X3 can cause muscle hypertrophy by targeting the key principles mentioned earlier.

Variable resistance provided by heavy-duty bands allows for optimal loading throughout compound movements, enabling you to recruit the large motor units that result in the most significant size increases.

In the strongest exercise positions, X3 can provide high forces, achieving much higher resistance than would be reasonable with weights. These high forces, coupled with a low rep speed (and thus slow muscle contractions), will ensure the largest muscle units are recruited and more cross-bridges are formed, leading to maximum levels of myofibril hypertrophy.

Lastly, because the X3 system provides optimized variable resistance, resistance becomes much lower when you are in your weakest range of motion. For example, with the X3 chest press, there is less tension at the weakest point of the lift, just above the chest.

Lower forces in weaker ranges of motion mean that you can do far more repetitions than you would expect, given the high peak forces in stronger positions.

When using X3, one might actually experience peak forces higher than their one-rep max with weights but still perform 30 consecutive repetitions because the force also decreases for the appropriate portion of the range of motion. Therefore, the same set can provide significant stimulus for both myofibril hypertrophy and sarcoplasmic hypertrophy.

X3 exercises are also compound movements that require self-stabilization, which can increase muscle activation and, therefore, muscle growth.

For more information on this system, check out Dr. John Jaquish’s new book, Weightlifting is a Waste of Time 5, or visit JaquishBiomedical.com 6.


  1. https://medium.com/@SandCResearch/explaining-how-hypertrophy-works-using-only-basic-principles-of-muscle-physiology-48beda5fbf1b ↩︎

  2. https://pubmed.ncbi.nlm.nih.gov/32205914/ ↩︎

  3. https://journals.lww.com/nsca-jscr/Fulltext/2014/04000/The_Acute_Hormon_l_Response_to_Free_Weight_and.22.aspx ↩︎

  4. https://www.researchgate.net/profile/John-Jaquish/publication/309736719_Stabilizing_Motor_R_flexive_Activation_and_Acute_Growth_Hormone_Response_A_Systematic_Review/links/582b3e9a08ae004f74afab5e/Stabilizing-Motor-Reflexive-Activation-and-Acute-Growth-Hormone-Response-A-Systematic-Review.pdf ↩︎

  5. https://www.jaquishbiomedical.com/book/ ↩︎

  6. https://www.jaquishbiomedical.com/x3-bar/ ↩︎

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