the science behind muscle hypertrophy

The Science Behind Muscle Hypertrophy

What happens in your body when you go to the gym? How do you build muscle?

In this post, we talk about muscle hypertrophy; the science behind building muscle!


Muscle Hypertrophy is known as an increase in muscle mass through addition of sarcomeres in parallel or increase on their size.

Guillermo, TBS

Muscle hypertrophy is the term used to describe the increase in muscle mass. Through this process, your muscle cells add altogether, forming a bigger cluster of fibers.

muscle hypertrophy

Muscle hypertrophy is the result of intense resistance training. The overload stimulus given when you lift weights trigger a chain of biological processes to contract the muscle, and ultimately produce an increase in muscle mass (source)


What Causes Muscle Hypertrophy?

Muscle hypertrophy cannot be explained by a single cause; it is a multifactorial phenomenon.

Are many the mechanisms by which muscle hypertrophy can be caused:

  • Satellite cells
  • Myogenic pathways
  • Hormones
  • Cell swelling
  • Hypoxia

Satellite Cells

Satellite cells are the precursors of muscle cells. With no function assigned, they wonder around your muscle, until they are transformed into a muscle cell to form the muscle tissue (source)

satellite cells

This cells are one of the main causes of muscle hypertrophy. First, satellite cells proliferate and evolve. The, they are differentiated into mature muscle cells, and fused to existing muscle.

This is the process by which satellite cells can contribute to muscle hypertrophy.

Myogenic Pathways

Metabolic pathways such as mTOR are responsible of upregulating muscle hypertrophy (source). Several other primary anabolic signaling pathways influence muscle hypertrophy, such as mitogen-activated protein kinase (MAPK), and calcium-(Ca2+) dependent pathways.

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Hormones and cytokines are largely contributors to muscle hypertrophy. Testosterone,  IGF-1, and GH are the strongest anabolic hormones in your organism.

The hormonal regulation of muscle hypertrophy is complex, with many hormones and cytokines believed to contribute to the response (study)

This molecules not only upregulate muscle hypertrophy, but can also influence fat loss.

Cell Swelling

Cell swelling, also known as cellular hydration, increases protein synthesis and decreases protein breakdown.

This process is maximized by strength exercise, in where the accumulated lactate in the muscle contributes to the hydration of the cells.



Hypoxia is the lack of oxygen in your muscles. It contributes to muscle hypertrophy by enlarging the effect of metabolic stress, one of the main mechanisms of muscle hypertrophy.

Hypoxia contributes to increases in muscle hypertrophy, with effects seen even in the absence of exercise (study)

With a lack of oxygen in your muscles, the production of ROS and myokines increase. These molecules favour muscle hypertrophy (study)

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The Mechanisms Behind Muscle Hypertrophy

Mechanical tension, metabolic stress, and muscle damage are the main mechanisms of muscle hypertrophy.

Designing your workout plan to optimize these three mechanisms will let you build muscle at a faster rate and more efficiently.


Mechanical Tension

Mechanical tension is the force created when a muscle contracts isotonically against a load. It is produced both by the force and stretch of the muscle.

When the force is generated on the muscle, it causes mechano-chemically transduced molecular and cellular responses in myofibers and satellite cells. This will ultimately lead in muscle hypertrophy

Although mechanical tension alone can produce muscle hypertrophy, it needs of the other two mechanisms to produce the needed effect to build muscle efficiently.

The factors affecting mechanical tension are the time under tension, heavy loads, the force-velocity relationship, and progressive overload.


Metabolic Stress

Metabolic stress, together with mechanical tension, are the two main mechanisms of muscle hypertrophy.

It refers to the accumulation of metabolites in the muscle cell after intense exercise. Lactate, among other waste products, start accumulating and causing different metabolic effects.

You can optimize metabolic stress by using lower loads, shortening resting times between sets, and using other techniques such as blood flow restriction training.

Muscle Damage

Muscle damage is believed to be a consequence of mechanical tension and metabolic stress (study).

Resistance training causes tearing of the membranes in your muscles and stretches molecular channel. The response to muscle damage increases satellite cells proliferation and differentiation into mature muscle cells.


Muscle hypertrophy is the increase of muscle mass by the addition of sarcomeres in parallel. Satellite cells, hormones, protein balance, cell swelling, hypoxia, and myogenic pathways regulate this process.

The main mechanisms by which muscle hypertrophy is achieved are mechanical tension, metabolic stress, and muscle damage.

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