Table of Contents
While the debate continues to rage on among fitness professionals, athletes, and researchers as to whether or not there is indeed a difference between muscle hypertrophy (growth) and Muscle hyperplasia (increase in the number of fibers), one thing is for sure: Muscle growth happens by both methods.
Muscle hypertrophy, or growth of the actual fibers, is due to an increase in the contractile proteins actin and myosin synthesis. In contrast, Muscle hyperplasia is an increase in the number of muscle fibers via the splitting of pre-existing fibers into two or more. Muscle fibers can do this, just like stem cells in the bone marrow. Muscle fiber splitting has been documented in numerous studies on animals and humans alike.
The Muscle protein actin is responsible for giving the Muscle its contractile properties. Actin assists myosin, another Muscle protein, to form cross-bridges between Muscle fibers, resulting in Muscle contraction. Muscle hypertrophy results from an increase in actin and myosin synthesis in Muscle fibers, which leads to Muscle fiber growth.
Muscle hyperplasia happens when Muscle fibers split apart and form new Muscle fibers. Muscle fibers increase in size via Muscle hypertrophy, and new Muscle fibers form due to Muscle hyperplasia. Muscle fibers can also grow by increasing myofibril density within Muscle fibers.
Muscle hyperplasia is often associated with Muscle growth in strength training, but Muscle hypertrophy generally contributes more Muscle growth in Muscle mass. Muscle hyperplasia is quite rare outside of very high-intensity strength training, while Muscle hypertrophy occurs in Muscle fibers subjected to both strength training and Muscle overload.
What Muscle hyperplasia means for you is that Muscle fiber number increases under certain conditions. Specifically, Muscle hyperplasia has only been shown to occur after training for local muscular endurance (such as failure-training), where repetitions go above 15 reps. Muscle growth happens regardless of whether Muscle hyperplasia occurs or not; the critical factor seems to be progressive overload, which means that you progressively lift heavier weights over time.
Progressive Overload refers to gradually increasing the stress placed on the muscles and nervous system during exercise over time to stimulate muscle adaptation due to its high efficacy. By setting different amounts of stress on your body, your muscles are forced to adapt by growing larger and stronger so they can keep up with the strenuous demands being placed on them. Muscle fibers respond to this kind of stress by splitting through a process called Muscle hyperplasia, resulting in Muscle growth.
While you can grow Muscle cells through progressive overload regardless of whether or not Muscle hyperplasia occurs, bodybuilders have more potential for this kind of adaptation since they contract their muscles at very high intensities, placing greater tension on the muscle fibers, which leads to an increase in muscle fiber number. Muscle hyperplasia allows you to pack on Muscle much faster, but Muscle hypertrophy still increases Muscle size.
Muscle Fiber Types
Muscle fiber types can be broken down into two main classifications (slow twitch and fast twitch), which refer to how Muscle fibers contract). based chiefly on their different functions: Slow-twitch Muscle fibers are the Muscle fibers that allow for endurance since they contract slowly and for an extended period.
Slow-twitch Muscle fibers have a more significant potential for muscle hyperplasia. Muscle hyperplasia explains how Muscle gains can happen as quickly as they do.
Since Muscle hypertrophy is simply Muscle fiber size increase, you will gain Muscle weight both in Muscle hypertrophy and Muscle hyperplasia. Muscle growth happens over time, but Muscle fibers split when forced to contract at high rates of force.
Muscle hyperplasia occurs regardless of Muscle fiber type, but it affects muscle size since the Muscle fibers are formed anew. Muscle fibers die rapidly when they are not stimulated by Muscle overload, which is why Muscle hyperplasia only occurs under certain conditions, where Muscle fibers are forced to contract at high force rates.
Muscle growth is possible both by Muscle hypertrophy and Muscle hyperplasia. Muscle fibers can split either through Muscle hypertrophy or Muscle hyperplasia. Muscle hyperplasia occurs when Muscle fibers are forced to contract at high rates of force.
Fast-twitch Muscle fibers are the Muscle fibers that allow for strength since they contract quickly.
Fast twitch ( FT ) Muscle fibers are classified as either type 2b or type 2a, depending on the specific characteristics of each Muscle fiber. Type 2b Muscle fibers can produce the most significant force out of all Muscle Fiber types, making them most useful for high-power movements like sprinting and rapid movements.
The majority of Muscle mass consists of Type II muscle fibers. However, these same Muscle fibers fatigue quickly due to increased myofibrillar density and reduced mitochondria activity within this specific Muscle fiber. Muscle fibers that fall into this category are often called fast-twitch Muscle fibers based on how quickly they fatigue and because of their incredible power potential.
Type 2a Muscle fibers work opposite to type 2b Muscle fiber: these Muscle cells generate less force than their type 2b counterparts but don’t tire as quickly and have better endurance than type 2b Muscle fibers. These Muscle cells contain more mitochondria and myoglobin, the former allowing for the generation of energy and the latter facilitating its transport from the muscles where it’s generated to other areas where it’s needed for other bodily functions. This may be why bodybuilders develop greater muscle mass compared to other athletes since their muscles need vast amounts of energy to support growth.
Muscle hyperplasia Muscle fibers are type 1 Muscle cells, increasing muscle fiber numbers even more impressive. Type 1 Muscle cells are just as powerful as type 2b Muscle cells, but they’re not used for strength-related activities since their endurance is low.
These Muscle fibers possess the fastest rate of contraction, which is why they help maintain posture and stabilize joints (also called tonic Muscle contractions). The most common location in which you’ll find this specific Muscle Fiber type is within the walls of your blood vessels, where it prevents them from collapsing.
Muscle hyperplasia seems to be happening six times more frequently in bodybuilders compared to non-bodybuilders. This may explain how bodybuilders can gain muscle mass at such a high rate despite the amount of Muscle damage they experience during training; Muscle hyperplasia allows Muscle cells to recover quickly and keep up with the increased Muscle fiber number.
The difference between Muscle hypertrophy and Muscle hyperplasia is a fine line. Both processes allow for increases in Muscle mass from Muscle cell proliferation. However, Muscle hypertrophy occurs due to the rise in size, whereas Muscle hyperplasia occurs due to an actual multiplication of Muscle cells.
How To Induce Muscle Hyperplasia
The current research suggests that Muscle fiber hyperplasia occurs during local muscular endurance training, where repetitions exceed 15 reps since it does not resist enough load tension. Muscle fiber hypertrophy, on the other hand, occurs through high-resistance strength training, which creates high enough tension forces resulting from heavy loads.
This theory also correlates with muscle response following heavy resistance exercise for men compared with women. In general, men form bigger muscles than women because they produce more testosterone, the male sex hormone which regulates muscle mass during puberty.
Muscle fibers can replicate themselves through a process called Muscle cell division. Muscle cell division is increased Muscle hypertrophy.
And while Muscle hyperplasia leads to an increase in Muscle fiber numbers only under certain conditions; Muscle hypertrophy involves both pre-existing Muscle fibers and newly formed Muscle fiber, but remember that you can grow Muscle cells by weight training regardless of whether or not Muscle hyperplasia occurs.
One study conducted in 2008 determined Muscle fiber growth by Muscle biopsy (a Muscle sample). Muscle samples were taken from the vastus lateralis Muscle of five healthy male subjects before and after ten weeks of intense Muscle training.
Muscle hypertrophy was observed, but Muscle hyperplasia was also noted in the Muscle samples. Muscle fiber splitting was seen in Muscle samples from all five Muscle subjects. Muscle fibers that were Muscle spindle-shaped had split into two Muscle fibers, while Muscle fibers with multiple nuclei had split into more Muscle fibers.
More than anything, Muscle growth happens when you break down your muscles through weight training to the point where they literally cannot lift any more weight, then get them back again more significant and more robust.
As long as you’re progressively lifting heavier weights over time (called progressive overload), your muscles will respond by growing larger so they can handle the intensity of future workouts. And since bodybuilders tend to have larger Muscle fibers, Muscle hypertrophy most likely accounts for most Muscle growth in this population.
However, Muscle hyperplasia can be a viable pathway for Muscle growth, but there are still many unknowns about Muscle fiber replication. The current thinking is that Muscle hyperplasia Muscle cell division only happens under certain conditions. Muscle fiber replication may not be possible without Muscle damage, which can also induce Muscle hypertrophy Muscle fiber growth.
Maughan, R. J., Selby, A., & Watson, J. S. (2007). Sports beverages and exercise performance Nutritional needs in sport and physical activity The Proceedings of the Nutrition Society 66(1), 166-176 DOI: 10.1017/S0029665107006177
Loenneke, J. P., Fahs, C. A., Rossow L, M., Abe, T., & Bemben, D. G. (2012). Muscle fiber composition and strength after resistance training Journal of Strength and Conditioning Research, 26(12) DOI: 10.1519/JSC.0b013e318247fe1a