Muscle building

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Muscle build-up refers to the enlargement of the muscles , which is caused by the loads involved in targeted training , such as B. in bodybuilding or body shaping , or by other types of increased physical resistance ( sport , work, etc.). When adapting muscles through muscle building, a distinction can be made between muscle hypertrophy , the thickening of existing muscle fibers, and muscle hyperplasia , the formation of new muscle fibers, the existence of which is controversial in humans.

Muscle hypertrophy

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Cells of normal size ( A ), in hypertrophy ( B ), hyperplasia ( C ) and in a mixture of both ( D ).

Muscle hypertrophy describes the enlargement of the muscle cross-section caused by the growth in the thickness of the muscle fibers , but not the increase in the number of muscle cells ( syncitia ). Muscle hypertrophy in this sense occurs when the muscles are stressed beyond their normal performance level, which triggers a so-called growth stimulus, which in turn causes increased protein storage (see anabolism ).

Muscle fibers are the constituent parts of a muscle. A muscle fiber is a muscle cell. Muscle cells are polyenergid cells; that is, they have several cell nuclei. Each cell nucleus has a certain "sphere of influence" which it controls through its gene expression. This "sphere of influence" is called myonukleare domain (Engl. Myonuclear domain , MND). The size of an MND has a maximum that results from the ratio of sarcoplasm and cell nucleus, which is determined in a muscle cell by the requirements of an optimal metabolism. The MND can enlarge through strength training , in which proteins are stored through anabolism . It does this by transferring mechanical stress into the muscle cell ( mechanotransduction ). Here are focal adhesion kinase (FAK) is activated, the set a chain of reactions in the sequence which the synthesis of muscle protein (e.g., contractile proteins such as actin and myosin , cytoskeletal proteins and enzymes of the citric acid cycle stimulate).

There are two major metabolic pathways: the mechanical (via MAPKp3) and a purely metabolic one (via MAPKerk1 / 2). The latter is activated by metabolic stimuli such as an oxygen deficit and hypoxic by-products such as lactate and oxygen radicals, and by changes in pH . It is assumed that the metabolic mechanism of action causes a significantly lower growth stimulus than the mechanical metabolic pathway. It rather leads to an adaptation of the oxidative capacity. The mechanical metabolic pathway is activated by microtraumas and is of greater importance with regard to hypertrophy, since, in addition to an increase in the protein biosynthesis rate , it leads to a fusion of satellite cells with the muscle cell, whereby the total amount of DNA in the cell increases and thus the hypertrophy potential increases.

Microtraumas are the smallest injuries to the cell, triggered by supra-threshold mechanical stress and, to a much lesser extent, oxidative stress. They lead to the production of muscle-specific IGF-1Ec ( insulin-like growth factor , also called mechano growth factor [MGF]), which penetrates to the outside ( paracrine secretion ) and sets in motion a so-called satellite cell cascade . Satellite cells ( myoblasts ) are a type of stem cells that are still largely undifferentiated and are located in the vicinity of muscle fibers. These are activated by the metabolic process mentioned, differentiate and move to the site of the damage to the cell membrane ( chemotaxis ), where they fuse with the muscle cell and thereby contribute their core as another nucleus of the muscle cell. This increases the total amount of DNA in the muscle cell and thus - due to new MNDs - the hypertrophy potential. Microtraumas are therefore essential for long-term effective training. The problem with building muscle is that, due to the synthesis of muscle protein, cytoskeletal proteins (supporting proteins) are also synthesized, which are supposed to protect the cell from mechanical overload. For this reason, the training must be designed progressively.

The exact, extremely complex mechanisms of hypertrophy are not yet fully understood, but thanks to new technologies such as magnetic resonance imaging , which can take three-dimensional images of individual muscles, and dual x-ray absorptiometry , hypertrophy has been researched in more detail in recent years. Most of the known, partly still popular, theories, such as the hypothesis of increased blood circulation, the muscle hypoxia hypothesis and the ATP deficiency hypothesis (the ATP level in the cell remains constant), have been refuted. Only the energy theory and the stimulus-tension theory remain theoretical, both of which, however, have been reduced to absurdity by the new findings as explanatory models.

Muscle hypertrophy, by external influence, such as specific training in bodybuilding , weight training or strength training can be achieved. In addition, the muscle growth triggered by training can be achieved through a suitable diet, e.g. B. by protein-rich food. In addition, muscle building can be artificially stimulated by exogenous factors, e.g. B. by taking anabolic hormones ( growth hormones or anabolic steroids ). These agents are usually used for medical therapies , but also for doping . In particular, their regular use for the purpose of building muscle carries great health risks.

The number of muscle cell nuclei increases significantly through anabolic steroids, training and protein (in animal experiments by 66%, muscle cross-section by 77%), after 3 weeks without anabolic steroids, the muscle cross-section had developed back to its original position. However, after 3 months (= 10% of the life expectancy of mice), the number of muscle nuclei was still so large that 6-day muscle training resulted in a 31% increase in muscle cross-section in the previously treated mice, but only by 6% in a comparison group that had never been treated. This not only shows the absurdity of the doping controls for anabolic steroids, but also refutes the MND hypothesis.

In a study by Morton et al. (2016) an attempt was made to show that it makes no difference for muscle building whether weights are heavy or light. Rather, it is important to use weights “to the point of exhaustion”: For the study, the scientists rely on two groups of test subjects made up of experienced weightlifters. Although one group had trained with less strength and many repetitions and the other group with almost maximum strength and few repetitions, the increase in muscle mass and muscle fiber size was almost identical after a few weeks. Other studies such as that by Schoenfeld et al. (2016) point out, however, that high weights lead to a higher gain in muscle mass. Due to the high metabolic stress associated with light weight and high repetitions, it is often easier to strain the muscle "to exhaustion" with high weight and few repetitions.

KAATSU training

KAATSU training (in Japanese the abbreviation for "resistance training combined with impaired blood flow") was developed as an effective method for rapid muscle hypertrophy - especially in the elderly and the untrained. Using a blood pressure cuff, the local removal of the fatigue substances, especially the lactic acid formed, is made more difficult, which leads to exhaustion more quickly. Despite initial fears, this training has no negative side effects.

Muscle hyperplasia

Under Muskelhyperplasie refers to a fiber propagation within the muscles.

This effect has not yet been demonstrated in humans. In some animals, such as the mouse, it has been demonstrated in laboratory tests with synthetic myostatin antibodies. Some researchers believe that the effect can be transferred to other mammals.

nutrition

Protein intake plays an important role in building muscle. Contrary to a widespread rumor that animal protein should perform better than vegetable protein in muscle building, scientists could not find any evidence for this. Rather, the value of protein plays a decisive role in building muscle and with the appropriate combination (e.g. wheat protein such as seitan plus soy protein such as tofu ) it is even higher than that of muscle meat or eggs. Another rumor concerns soy proteins , which at 85 have a high biological value, but which allegedly contain high amounts of estrogen- like substances; in fact, however, these amounts are very small and studies have not shown any harmful effects.

Schoenfeld et al. (2013) found no connection between the point in time at which protein was consumed and training success in a meta-study; accordingly, the only thing that matters when building muscle is the daily amount of protein and by no means the timing. Recommendations that used to be common, according to which proteins should best be taken within an hour before or after training (anabolic or metabolic window), have been largely refuted.

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Individual evidence

  1. ↑ cf. Egner, Bruusgaard et al. (2013): A cellular memory mechanism aids overload hypertrophy in muscle long after an episodic exposure to anabolic steroids, in: Journal of Physiology 591 (24), 6221-6230.
  2. ↑ Arnd Krüger (2019): Muscle Memory, in: Leistungssport 49 (3), 32.
  3. ↑ RW Morton, SY Oikawa, CG Wavell, N. Mazara, C. McGlory, J. Quadrilatero, BL Baechler, SK Baker, SM Phillips: Neither load nor systemic hormones determine resistance training-mediated hypertrophy or strength gains in resistance-trained young men. In: Journal of applied physiology. Volume 121, number 1, July 2016, pp. 129-138, doi: 10.1152 / japplphysiol.00154.2016 , PMID 27174923 , PMC 4967245 (free full text).
  4. ^ Brad J. Schoenfeld, Jacob M. Wilson, Ryan P. Lowery, James W. Krieger: Muscular adaptations in low- versus high-load resistance training: A meta-analysis . In: European Journal of Sport Science . tape 16 , no. 1 , 2016, ISSN  1536-7290 , p. 1–10 , doi : 10.1080 / 17461391.2014.989922 , PMID 25530577 .
  5. ↑ Arnd Krüger : KAATSU training. In: competitive sport. 41 (2011) 5, pp. 38-41.
  6. ↑ JP Loenneke, RS Thiebaud, T. Abe: Does blood flow restriction result in skeletal muscle damage? A critical review of available evidence. In: Scand J Med Sci Sports. March 20, 2014. doi: 10.1111 / sms.12210 .
  7. ↑ Se-Jin Lee: Regulation of muscle mass by myostatin. In: Annu. Rev. Cell Dev. Biol. 2004. April 21, 20, 2004, pp. 61-86.
  8. ↑ KM Mangano, S. Sahni, DP Kiel, KL Tucker, AB Dufour, MT Hannan: Dietary protein is associated with musculoskeletal health independently of dietary pattern: the Framingham Third Generation Study. In: The American journal of clinical nutrition. Volume 105, number 3, March 2017, pp. 714-722, doi: 10.3945 / ajcn.116.136762 , PMID 28179224 , PMC 5320406 (free full text).
  9. ↑ Hamilton-Reeves et al. (2010), PMID 19524224 .
  10. ↑ Schoenfeld et al., (2013), doi: 10.1186 / 1550-2783-10-53