Hypertrophy and muscle growth, how does it work?

Bodybuilders generally ask themselves relatively few questions about how they gain muscle and strength. For them, it's enough to follow their training program, performing a high volume of exercises with maximum intensity. Along with this, they also know that protein is essential for muscle gains as well as maintaining strength. They'll tell you that carbohydrates and fats provide energy, and perhaps also that they eat pasta and red meat because they provide creatine.

At this level, we're not far from clichés, but athletes aren't necessarily specialists in organic chemistry. In reality, the various processes that trigger muscle growth, in other words, the hypertrophy of skeletal muscle fibers, are particularly complex. Some details related to these processes remain unknown to this day .

Muscle growth, a physiological adaptation reaction of the body to physical stress

If we had to define what muscle growth through hypertrophy is, we would simply say that the body adapts to neuromuscular stress that it has had to endure over a period of time. This adaptation results in the muscle fibers increasing in mass, volume, and strength in order to be able to cope with the same type of stress if it were to occur again (in other words, at the time of the next training session).

So, muscle growth responds to many principles of stress and exercise recurrence. It can involve strengthening the muscle fibers themselves, but also an increase in sarcoplasm with a gain in glycogen and muscle cell volume. The nature of your workouts will determine whether they lead to hypertrophy of the sarcomeres (the fibers themselves) or the sarcoplasm (the cellular environment that contains glycogen and nutrients). Still, explaining this process simply may be much more difficult. However, let's try to start at the beginning...

Intense strength training results in micro-tears to be compensated for by functional hypertrophy

When you perform intense strength training exercises, you will exceed a certain threshold. This is a natural adaptation threshold to the exercise. If you take on a heavy and unusual load for your muscles, micro-tears will form in certain areas. This means that your usual work capacity has been exceeded. From then on, your body will have to adapt by strengthening the fibers damaged by the exercise. When this happens, multiple biological mechanisms will be activated. On the surface of these processes, amino acids will be recruited to rebuild the damaged fibers, all of this being precisely controlled by your genetics, which will allow a greater or lesser strengthening of the mass and volume of your muscles.

What are the main factors in muscle hypertrophy?

Physiologically, dozens of different molecules will be activated in your body to trigger the synthesis of your own proteins. What you need to consider here is the state of your muscle glycogen stores. If they are too low, the amino acids present in the muscles will be quickly broken down to make glucose again. Clinical experience shows that taking a carbohydrate drink after training stops muscle catabolism without activating protein synthesis, probably due to the lack of available amino acids.

Carbohydrates will, however, replenish glycogen, the first step in post-exercise recovery. Conversely, taking whey protein will reactivate anabolism, allowing immediate glycogen needs to be met by breaking down amino acids to make glucose, while also using them to reactivate muscle protein synthesis.

Leucine is involved in the activation of muscle fiber anabolism.

Leucine is the branched-chain amino acid that kicks off the complex processes of muscle hypertrophy. However, without the other essential amino acids, it will be ineffective in growing your muscles. Its presence in high quantities will activate several enzymes, including the famous mTOR and Akt complex, which you may already be familiar with. A cascade of enzymes will ultimately lead to the synthesis of your muscle proteins, a bit like millions of needles and threads starting to knit together.

However, for this cell-building process to be effective at the cellular level, the presence of proteins and essential amino acids is imperative, we must repeat. Without them, muscle mass and strength gains will be non-existent, resulting in regression rather than any gain in muscle mass. This complex recovery system can extend over 3 to 5 days AFTER training and not the 4 to 5 hours that follow.

Hypertrophy of skeletal muscle fibers is a physiological process that lasts at least 3 days…

It's also important to know that the adaptation of a trained muscle can last three days on average, sometimes up to five days. We know this thanks to inflammatory markers such as interleukins IL-6 and IL-12 in particular. This gives you an idea of ​​the importance of nutrition after the intense exercises you perform. This also means that adaptation through hypertrophy and muscle strength gains never stops, as long as you don't stop the successive workouts performed in the weight room.

Beyond these complex compensation mechanisms, hormones play a key role in muscle growth, particularly testosterone and its derivatives, but it is not the only one. Growth hormone and its metabolites such as IGF-1, IGF-2 or MGF also have an important role to play in the amplitude of skeletal muscle fiber hypertrophy, in close relation to other proteins that you have probably already heard of, such as myostatin and follistatin, for example...

Nutrition is the key and major element of post-exercise muscle hypertrophy

Nutritionally, you've probably figured out that protein is important for strength athletes, even more so than for endurance athletes. However, carbohydrates remain the primary nutrient for energy and recovery, as post-exercise hypertrophy requires large amounts of ATP and therefore carbohydrates. Without sufficient carbohydrate intake, you won't be able to truly benefit from your creatine , as the two are indirectly linked in terms of energy.

Let's also add that some micronutrients that are too often forgotten are also necessary for muscle growth and strength gain. For example, thiamine ( vitamin B1 ) initiates the conversion of glucose to pyruvate, the first step in the conversion to ATP and the energy it releases. Generally speaking, B vitamins are essential for energy release. Vitamin B2 is the precursor of FAD, a coenzyme of the Krebs cycle, while niacin (vitamin B3) will be the precursor of NAD+, an even more essential coenzyme in terms of energy . Vitamins B9 (folates) and B12 (cobalamin) are often forgotten. However, folic acid is essential for cell division, which can be "handy" when talking about hypertrophy. Vitamin B12 works synergistically on folic acid metabolism.

Naturally, it is impossible for us to go into detail about the different metabolisms that need to be addressed in the context of muscle fiber hypertrophy, the subject is so vast. In fact, it exceeds the length of a book. However, we hope that these basic explanations will help you better understand how and why you gain muscle. In short, if you become stronger and more muscular, it is because you have forced your body and your muscles to become so through strength training. Beyond these purely physiological considerations, we especially hope that you will have the opportunity to continue your sporting activity until a very old age...