What Is Hypertrophy? – Definition

In this article we will discuss muscle hypertrophy, a scientific term used to describe the physiological process of new muscle tissue development. Muscle hypertrophy is a key training process for every single athlete and lifter, regardless of sport, training level, or age. In the below sections we will outline what hypertrophy is defined as, the benefits and potential negatives (yes, there are some) to training for hypertrophy, and why strength and power athletes need to be aware of sarcoplasmic vs. myofibril hypertrophy.

What Is Hypertrophy?

Most of us think about a bodybuilder when we hear the word, “hypertrophy”. Truth of the matter is, there are potentially two different forms of muscle hypertrophy. I say potentially because some of this is science theory, as we are still learning as much as we know about the training adaptations that take place relative to volume intensities.

Sarcoplasmic and myofibril muscle hypertrophy both can build muscle, but have been thought to have some differences that play a critical role in the overall strength and power production capacities of an athlete. Below, we will break down what exactly sarcoplasmic vs myofibril hypertrophy is theoirzed as, and why coaches and athletes should fully understand the difference to best develop strength, power, and fitness athletes.

Sarcoplasmic Hypertrophy

Sarcoplasmic hypertrophy is thought to occur within the sarcoplasm of the muscle cell, in which this space expands, therefore increasing muscle size. While muscle fiber growth does exist, it is thought that sarcoplasmic hypertrophy may have a larger impact on sarcoplasm growth, rather than strictly increasing growth of the individual muscle fibers/myofibrils.

Suppose you had five pull-and-peel licorice sticks in your hand, each representing a muscle fiber. When training for sarcoplasmic hypertrophy, you are essentially increasing the space between the sticks (muscle fibers), rather than increasing the size or density of the muscle fiber or it’s individual components (myofibrils, see below). Note, that this is still a theory that has not been shown (or disproven), and further research into this must take place. It is also important to note that hypertrophy is not a one or another, as it can occur in both the sarcoplasm and individual myofibril.

Myofibril Hypertrophy

Myofibril hypertrophy results in increased muscle fiber growth and strength capacities, however it does not necessarily increase the visible, measurable size of a muscle (as much as sarcoplasmic hypertrophy training). To use the example of the pull-and-peel licorice sticks from above, we need to actually take a deeper look within the muscle fiber itself.

In this example, let’s say you have an entire sealed bag of pull-and-peel licorice sticks, which now represents one muscle fiber. Each muscle fiber (sealed bag) contains 10 sticks of pull-and-peel licorice, each now representing a myofibril (one pull-and-peel licorice stick). If you were to then unpeel each individual stick, you would be left with multiple contractile units (individual strand of licorice) within the myofibril. The below image can be helpful in this breakdown.


During myofibril hypertrophy training, you increase the number of myofibrils (individual peel-and-pull licorice stick) within a single muscle fiber (increased muscle density) and therefore increase the amount of contractile units within each individual muscle fiber (sealed bag).

3 Benefits of Hypertrophy

Below are three benefits of hypertrophy training, either specific to sarcoplasmic hypertrophy or myofibril hypertrophy. While there are some distinct differences between the two types of hypertrophy (see section above), the below benefits can generally apply to both types and most lifters. Note, these are three main benefits of hypertrophy training, but not all of them.

More Muscle

At the simplest of levels, hypertrophy training has the ability to increase muscle fiber growth, muscle visible size, and capacities for strength and power output (when trained in a more sport specific manner). Periods of hypertrophy training are a normal part of every athlete’s year-long training cycle.

Injury Resilience

Increasing muscle growth, blood flow, and foundational physiological outcomes (motor-learning, aerobic and anaerobic capacities, etc) necessary for more rigorous training cycles all aid in an athlete’s ability to resist injury throughout their training career.

Greater Strength and Power Production Capacities

As discussed in the last section, myofibril hypertrophy is responsible for increases in muscle fiber growth and contractile units (strength potential), whereas sarcoplasmic may not have as much of an impact (however, strength and power athletes can still benefit).

When taking times out of the year to train for hypertrophy (either type), an athlete can set themselves up for increased training demands as they approach competition/more intensity-driven cycles.

Potential Negatives of Hypertrophy

To be honest, there aren’t a lot of issues here with building serious muscle mass, strengthening a foundation of movement, or enhancing an athlete’s resistance to injury. That in mind, there are a few things that coaches and athletes need to be aware of when programming hypertrophy-focused cycles/session into an athlete’s regimen.

Decreased Power Output

Research suggests that higher-rep, shorter-rest period training programs can actually decrease an athlete’s maximal power output, especially in more advanced (stronger) athletes. This is just one potential reason why coaches program hypertrophy (moderate to higher rep) cycles farthest out from competitions where peak force and power outputs are key (strongman, powerlifting, and Olympic weightlifting).

Practical Applications

When programming accessory work or hypertrophy phases for strength, power, and fitness athletes, coaches must have a solid grasp on which type of muscle hypertrophy will be the most beneficial to their athletes.

Training for General Hypertrophy

As a starter, most athletes and lifters at some point in their development should go through a stage of hypertrophy that that uses moderate loading and repetition ranges. This is is often a starting point for beginner and intermediate fitness goers looking for general increased muscle growth, size, and increased work capacity. For most beginners and intermediate lifters, simply doing any style of hypertrophy (moderate to higher rep ranges) will build muscle mass, size, strength, and increased readiness for more advanced training.

How Should Strength and Power Athletes Train Hypertrophy?

For most of us, myofibril hypertrophy should be the focus, as it leads to increased muscle fiber growth and the ability to acquire strength (via increased force outputs). Additionally, it develops a muscle tissue into a lean and compact unit. To develop myofibril hypertrophy, higher intensities (70-90% RM) for less reps (3-6 repetitions) are thought to be best, however once again, nothing here has been proven or set in stone. Note, that higher rep-based hypertrophy training does have additional benefits that strength and power athletes should consider, such as increasing blood flow and nutrient to damaged muscles, enhancing aerobic capacities of the tissues, and can be helpful in injury prevention.

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