Muscle hypertrophy - how do our muscles grow Increase in Muscle volume

Muscle hypertrophy, Increasing muscle mass and increasing muscle volume is among the goals of a number of professional athletes and ordinary fitness enthusiasts. But how do our muscles grow and what are the mechanisms by which this happens?

Table of Contents

In the following lines you will learn:

The main way our muscles grow is called muscle hypertrophy;
Muscle hypertrophy is myofibrillar and sarcoplasmic;
The main known mechanisms of muscle hypertrophy are mechanical tension, muscle damage and metabolic stress.
Mechanical tension is the most important mechanism of muscle hypertrophy.

Structure of muscle tissue

Muscle tissue has an interesting and unique structure. While in most tissues, the cells that make them up are circular in shape and contain a single cell nucleus, muscle cells are different. Muscle cells are long and cylindrical with a diameter of about one human hair and instead of just one, they contain many cell nuclei located along the entire length of the cell. Most readers are probably familiar with the term muscle fiber. Well, you may be interested to know that virtually every muscle fiber is a separate muscle cell that extends from the beginning to the end of each muscle.

Each muscle cell / fiber contains a variety of components, such as mitochondria, glycogen, fat particles and the most important for weight trainers – the contractile proteins called myosin and actin, thanks to which our muscles can contract. The individual muscle cells / fibers are grouped into separate bundles and the group of all bundles forms our muscles – as we are used to seeing them when we look in the mirror.

How do muscles grow?

Muscle growth can be described in various terms. In theory, muscles can grow in length (serially) and in width (in parallel), but since it is probably clear to everyone that muscle length cannot be changed significantly, at least not through standard weight training, muscle growth for the most part it happens at latitude. First, muscle growth can occur through:

muscle hypertrophy;
muscle hyperplasia.

In muscle hypertrophy, muscle cells grow in volume / size, while in muscle hyperplasia they grow in number.

At this stage, it is not yet completely clear whether and to what extent muscular hyperplasia is possible and the reason is mainly that it is extremely difficult to trace such a thing experimentally. Imagine having to count all the hairs on a human head, but at times a more complicated option. Even animal experiments are difficult to answer. However, most experts agree that even if there is muscle hyperplasia, it contributes minimally to muscle growth. Accordingly, at this stage, muscle hypertrophy is considered the main way in which our muscles grow. Muscle hypertrophy, in turn, can be:

myofibril;
sarcoplasmic

In myofibrillar muscle hypertrophy, growth occurs in the contractile proteins in muscle cells – the aforementioned myosin and actin. Myofibrillar hypertrophy is sometimes called functional, because in practice only it has a direct and immediate effect on the generation of force. In sarcoplasmic muscle hypertrophy, growth occurs due to the other elements contained in the cell – mitochondria, glycogen and others. The sarcoplasm is actually the fluid (cytoplasm) that also contains myofibrils.

In fitness circles, you may still find a debate about how certain training protocols target and lead to (mostly) sarcoplasmic muscle hypertrophy, while other protocols target and lead to (mostly) myofibril. Many people explain the difference in strength and size between bodybuilders and strength athletes based on their muscle structure. Bodybuilders are older, but often can’t lift as much as strength athletes, because their muscle hypertrophy is mainly sarcoplasmic, and strength athletes are myofibrillar. Or so it is claimed.

Therefore, online and offline there are still claims that if you want to become strong, you need to train with low repetitions (high intensity), as this is the target of myofibrillar hypertrophy. Accordingly, if you want to be great as a professional bodybuilder, you need to train with high repetitions (low intensity). However, this is not true. Sarcoplasmic hypertrophy can indeed be targeted, without the need to even train. One or two days of a high-carbohydrate diet to increase glycogen stores in muscle cells, a little creatine supplementation and here’s sarcoplasmic hypertrophy.

Certain training protocols with lower intensity, allowing more repetitions to be performed, also lead to a more significant increase in stored glycogen and water levels. During the first weeks, novices in weight training also have greater water retention in the cells due to the more serious muscle damage they are subjected to. In other words, yes, in the short term, sarcoplasmic hypertrophy can outnumber myofibrillar hypertrophy. However, in weightlifters, whether and how exactly exercise protocols affect sarcoplasmic hypertrophy, not only in the short term but especially in the long term, is not clear at this stage and is extremely difficult to answer.

Just like hyperplasia, sarcoplasmic hypertrophy can be ignored at this stage, at least until science advances. It turns out that it cannot be avoided and will happen regardless of the training protocol, but how this changes over time (months, years) remains to be seen. We at BB-Team believe that it is far more reasonable and practical to train without attempting to target a particular type of muscle hypertrophy, especially given the fact that it has been repeatedly proven that general (including myofibrillar) hypertrophy it can be approximately the same in degree for both low-intensity and high-intensity training.

Basic mechanisms leading to muscle growth

Our body is a highly adaptive system and muscle growth is one of the types of adaptations it is capable of. In general, our body wants to maintain a certain balance (homeostasis). In order to feel the need for adaptation, a stimulus (stress) must be exercised on it to upset this balance. This process of stimulus and adaptation is known in the scientific literature as General Adaptation Syndrome (GAS) (6) ⁠, whose specifics, however, are beyond the scope of this article.

For readers of this material, the main stimulus for muscle growth is resistance training. For example, when we train with weights in the gym, this activity is a stimulus leading to the activation of various mechanisms leading to muscle hypertrophy. One of the first works on the mechanisms of muscle growth and muscle hypertrophy, which is actually one of the cornerstones in the sports scientific literature, is The mechanisms of muscle hypertrophy and their application to resistance training by Brad Schoenfeld.

The three main mechanisms of muscle growth are:

mechanical tension;
muscle damage;
metabolic stress.

After writing this paper and expanding the scientific database, to date we have a little more clarity about how important each of them is.

Mechanical stress

Mechanical tension is the tension to which our muscles are subjected during their contraction. We generate such tension when we work out in the gym, when we run, jump or perform any activity that requires muscle contraction. When we put muscle fibers under tension, their integrity is disrupted, which in turn causes a specific chemical activity – a process called mechanotransduction. Various growth factors (eg IGF-1), myokines (eg IL-6) and a number of others are secreted, signaling the need for the muscle cells in question to be repaired.

These signals reach an enzyme complex called mTOR (mammalian target of rapamycin), which reads the information from these and other signals (for example, the presence of certain amino acids), and then sends this information to our genes (translation initiation). Our genes, in turn, contain the structural plans of various proteins, and in this case, start the implementation of processes that build new muscle tissue. The process that makes up muscle tissue is basically a basic one and is called muscle protein synthesis (MPS). However, simply stimulating muscle protein synthesis does not guarantee that we will become more muscular, because in parallel with protein synthesis, a process of muscle protein breakdown (MPB) occurs.

Synthesis and breakdown of muscle tissue occurs constantly, around the clock and simultaneously. Sometimes one prevails, sometimes the other. Depending on whether synthesis or breakdown predominates in the long run, we increase or lose muscle mass. Along with muscle protein synthesis, an equally important process called myonuclear addition occurs. In this process, so-called satellite cells located around the myofibrils donate new and additional cell nuclei to fuse with other muscle cells.

The donation of new cell nuclei is necessary (although some data suggest that it may not be necessary, at least in the short term because, as shared above, each muscle cell / fiber contains many cell nuclei, which are scattered along the entire length of the fiber. Each nucleus has the ability to control a strictly fixed area of muscle fiber (known as the myonuclear domain). When muscle fibers grow, there is a time when the available muscle nuclei are not enough to support and manage the new tissue, so over time and along with muscle growth, there is a need for additional nuclei.

Although beyond the scope of this article, we will briefly mention that a well-supported theory states that each person’s muscle potential largely depends on the number of satellite cells he possesses and the number of muscle nuclei that can be donated. People with more can build more muscle tissue, while those with less have a lower limit. The role of mechanical stress in muscle growth is indisputable and in fact it is considered the most important mechanism.

Muscle damage

In effect, muscle damage is the rupture and disruption of muscle cell integrity, literally. Until relatively recently, muscle damage was also thought to be an important mechanism for muscle growth. Many training programs and recommendations of coaches and professional athletes have been (and often still are) aimed at creating more muscle damage in order to lead to greater muscle growth. The reason for this is that muscle damage itself also stimulates the building of new tissue.

In recent years, however, a number of data have called into question the benefits of muscle damage to muscle growth. At this stage, the opinion of most experts is that muscle damage is part of the process of muscle growth, but the stimulated processes as a result of them aim to simply and simply repair the damage, without, however, building on them in any way. That is, more muscle damage does not lead to more muscle growth. They can even have a negative effect, because before the upgrading and building of new tissue begins, the body will first have to repair the existing damage, and the greater they are, the harder and slower everything will become.

Muscle damage cannot be completely avoided and it is not necessary to look for a way to reduce it intentionally, but it is also not advisable to look for a way to increase it.

Metabolic stress

Metabolic stress is the accumulation of secondary substances in cells. During training relying mainly on the body’s anaerobic energy system, as a result of the glycolysis process, by-products such as lactate, inorganic phosphate, hydrogen ions and others are released. Metabolic stress is the cause of that burning and pumping during a long series.

Metabolic stress is thought to contribute to muscle hypertrophy by increasing muscle fiber activation, stimulating the secretion of various hormones, leading to cellular bloating, and others ⁠, but nowadays the importance and contribution of this factor to muscle growth is also subjected to a big question. In practice, there are several commonly used ways in which the accumulation of metabolic stress can be achieved. One way is to maintain shorter breaks between sets and exercises, as this does not allow the body to dissipate the accumulated secondary substances.

However, scientific data show that although hypertrophy is achievable with short breaks (less than 60 seconds), longer breaks (more than 60 seconds, preferably even 120 seconds) lead to greater hypertrophy. The main reason for this is that, other things being equal, with longer breaks the trainee has the opportunity to perform more repetitions of each series, which leads to a larger training volume and because the training volume is the most significant training parameter for muscle hypertrophy, most volume leads to more muscle growth.

Another way to achieve higher metabolic stress is to train with a higher training volume and lower intensity. In other words – the use of weight allowing the performance of more repetitions (6-12 and up). The more repetitions are performed, the more metabolic stress accumulates. Here, however, the scientific literature also shows that with controlled total training volume, muscle hypertrophy is approximately the same at both high and low intensity (high and low repetitions).

Failure training also leads to significantly higher metabolic stress, but many scientific data show that failure training does not lead to better results and better muscle hypertrophy. They can often even negatively affect in the long run.

Last but not least, if there is a method to give a clearer answer to the relationship between metabolic stress and muscle hypertrophy, it is the KAATSU training method, also known as blood flow occlusion / restriction training. ), which due to its nature leads to a very large accumulation of metabolic by – products, respectively high metabolic stress. Blood flow restriction training has repeatedly been shown to be effective for muscle hypertrophy. Through them, when using very low intensity (20-40% 1RM), the same muscle growth can be achieved as with standard high intensity training (70-80% 1RM).

At first glance, this training method is a good proof of the role of metabolic stress in muscle hypertrophy, but the problem is that in the sports literature the study of metabolic stress is combined with the main proven mechanism – mechanical stress. This makes interpreting the results and drawing hard conclusions very difficult. It can be argued that if metabolic stress plays a role in the process of muscle growth, then its influence is indirect, by improving / increasing the mechanical load (by increasing muscle activation), which in turn stimulates hypertrophy.

How best to increase metabolic stress in resistance training and whether it is worth it at all remains to be seen.

Systemic factors

Under systemic factors are mostly hormones, in particular testosterone, growth hormone and IGF-1. It is known that exogenous (external) intake of supraphysiological doses of the hormones in question can significantly increase muscle hypertrophy, and that experimental blocking and reduction of levels of these hormones can compromise the increase in muscle mass and strength. Because there has been a significant but short-lived rise in levels of these hormones after resistance training, it has long been unclear whether these changes have a direct effect on muscle hypertrophy.

Probably there are still recommendations such that complex, multi-joint exercises should be present in the training, as some data show that they stimulate and increase hormone levels a little more than the isolating exercises and this leads to greater muscle growth. However, it is important to distinguish between pharmacologically stimulated and natural changes in hormone levels. The increase in testosterone levels after weight training is often in the range of 0.1% to 1% of the dose taken exogenously. The duration of this increase is approximately as short.

At this stage, the scientific literature is of the opinion that natural changes in hormone levels after exercise do not affect hypertrophy. If they have one, it is extremely small and should not be taken into account by the trainees.

Conclusion for Muscle hypertrophy :

The topic of muscle growth is one example of the evolution of sports science literature. Although there is still much to learn, at this stage muscle tension remains the main mechanism leading to muscle growth and it should be the focus of resistance training. Of course, the activation of a mechanism is not always a guarantee that over time the degree of muscle growth will be significant. This is influenced by a number of other factors, which, however, we will consider in a separate article.

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