Internal Development Theory

One of the data that complicates the Hormone Theory comes from studies of growth hormone supplements. Hormone Theory demonstrates muscle enlargement in those taking growth hormone supplements, based on the claim that hormones such as growth hormone increase muscle mass. However, studies show that if the person taking the supplement already has a hormone deficiency, there is growth in muscle mass. If the person is healthy, supplementing with growth hormone does not increase muscle mass.

According to studies, post-exercise hormone increases do not increase anabolic signaling or protein synthesis in myofibrils immediately after exercise. In addition, there doesn’t seem to be any need for testosterone or growth hormone for strength gain and muscle growth. Rather, studies show that mechanisms intrinsic to skeletal muscle tissue trigger anabolism under load. This indicates that muscle growth is not caused by a secondary factor such as hormones, but directly by internal factors.

According to the researchers, the most important of the signaling proteins intrinsic to the muscles is a protein called p70(S6K), and its acute increase after muscle training increases muscle protein synthesis and exhibits a more linear pattern with muscle growth. Of course, these are triggered by the loading of the muscles and thus the accumulation of protein in the muscles. The main elements that play a role in the internal development of the muscles are the molecules produced in the membranes of the muscle cells and the myofibril chemical pathways that feel under load.

Hyperplasia Theory

The most widely accepted mechanism of muscle development today is a phenomenon called hyperplasia. In essence, hyperplasia is quite similar to the Microtrauma Theory: As long as the muscle is working, the fibers are constantly contracting and relaxing. However, when the weights per fiber are calculated with the weights lifted, it is seen that the masses are lifted far above the strength of the fibers. In this case, the muscle fibers are simply torn. However, since there are millions of fibers in even a single arm muscle, this tear is neither felt as pain nor as a deficiency. It only manifests itself with a few days of soreness in the arms after the muscle has worked. However, the number of fibers breaking each time is so small compared to the total that these breaks have little effect. But the effect of breaking begins to be seen after long periods and months of work. Let’s explain this through an image that we showed in detail in our previous article:


Hierarchical structure of muscle

Here, let’s consider a single muscle strip. What we’re dealing with is the very thin strip (myofibril) shown at the end, not the thicker ones. We can understand the smallness of myofibrils as follows: A single myofibril is 1–2 micrometers (one millionth of a meter) thick, and each myofibril is approximately 2.5 micrometers long. Therefore, by joining them end-to-end and on top of each other, long muscle strips are formed.

Here, when we work the muscle, when we force 60% of the maximum load we can lift, the blood flow to the muscles is temporarily stopped and the myofibrils begin to break during this process (a minor to moderate tear is also shown in the image above). The pain you experience after muscle training is due to the rupture of a few tens or hundreds of billions of myofibrils. During the work, many myofibrils break in this way and our muscles begin to ache because of this.

But then, within 24–36 hours after the workout, the body begins to repair the muscles. At this moment, something interesting happens: Imagine that one of your myofibrils, attached to other myofibrils at two ends, snapped during operation. This strip is regenerated after splitting in half. However, the two ends of the myofibril cannot find each other and are attached to other myofibrils on the opposite side. For this reason, as a result of treating a single ruptured myofibril, 2 new myofibrils are produced. When this continues for months, new muscles are produced and muscle mass increases.

For this reason, after working the muscle, the muscles should be rested for at least 72 hours and allowed to repair. Because as you can see, muscle building happens while the muscle is resting, not when it’s working. Working out muscles every day will not do you any good. Rest is not a waste of time in muscle development, on the contrary, it is a benefit. In this process, you should support the fast and strong repair of your muscles by feeding, and you should ensure that the repair is done by getting plenty of sleep.

There is an abundance of academic studies supporting this theory. For example, in a study on rats, muscle hyperplasia was observed after resistance training. In a study on 10 elite athletes, muscle fibers with a smaller diameter and thus newly formed muscle fibers could be detected histologically compared to the control group. In another study, it was observed that very small myofibrils with central nuclei form in people who cycled for 6 weeks. In a study in cats, only 1 leg muscle was trained for 101 weeks and 9% more muscle fibers were detected in that leg. The results of this study were confirmed by a subsequent repeat experiment. A review of biopsy samples from muscle builders and weight lifters found evidence of hyperplasia in human muscles as well.

However, not all studies support this theory. For example, in one study, muscle fibers in the biceps of bodybuilders were examined and no new fiber formation was observed. In another study, signs of hyperplasia were searched in exercisers, but no evidence of new fibers was found. According to the authors of this study, previous research discovered new muscle fibers not because they actually formed, but because the researchers’ fiber counting methods were prone to error.

Despite all these contradictory results, studies scanning the academic literature in general indicate that the general opinion among experts regarding muscle development in animals is in favor of the hyperplasia mechanism. However, the issue of muscle formation in humans in the same way as in other animals tested is still controversial. No evolutionary difference is expected; however, it has not yet been conclusively confirmed in humans that hyperplasia is the main muscle growth mechanism.

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This article is an excerpt from by Karl Liebermann | Jun, 2022 | Medium