What is the science behind building muscle

Muscle building - what you need to know about physiology, training & nutrition

Muscle building, i.e. the increase in muscle mass or the enlargement of the muscle cross-section, is also known in science as muscular hypertrophy.

In the 80's, muscle building training was primarily popular with bodybuilders. Today, building muscle mass is one of the most common training goals in the gym. The reasons for building muscle can vary from person to person. The majority of those who build muscle do so for aesthetic reasons. Others would like to achieve an increase in physical performance through the larger muscle mass. Health aspects can also be the intention for muscle building training.

In the following article, the physiological fundamentals of muscle growth and the influencing factors will be discussed. Then the most important training parameters for optimal muscle building training are explained and exemplary training plans are presented. Finally, an insight into the elementary basics of nutrition for successful muscle building is given.

Muscle Growth Physiology

To understand how muscle building works, it is essential to first understand muscle anatomy. The following graphic shows the anatomical structure of a human skeletal muscle.

A muscle consists of several muscle fiber bundles. These are made up of several muscle fibers. A muscle fiber, in turn, consists of several sarcomeres. This is the smallest functional unit of the skeletal muscles. Sarcomeres contain the contractile elements Actin and Myosin (cf. structure of a muscle). Contractile means that these elements allow the muscle to contract.

A muscular cross-sectional enlargement can be achieved by two mechanisms: by the sarcomere as well as through the sarcoplasmic Hypertrophy.

Sarcomere hypertrophy

Strength training creates an intense tensile load on the muscle. The mechanical overload of the muscle leads to a disruption in the structure of the muscle fibers and the associated extracellular matrix. There is an adaptation reaction of the body, which tries to protect itself from future stresses of the same kind. In the regeneration phase, the number of sarcomeres is increased.

The new sarcomeres arise in parallel to the existing sarcomeres. This is why parallel hypertrophy is also used. The result is an increase in the diameter of individual muscle fibers and thus an increase in the overall muscle cross-section.

This hypertrophy mechanism is also described in the literature under the terms protein catabolism or theory of mechanical repair.

Sarcoplasmic hypertrophy

In addition to an increase in contractile elements, an increase in muscle cross-section can also result from an increase in various non-contractile elements and fluid. This is called sarcoplasmic hypertrophy.

The accumulation of glycogen in the sarcoplasm has a decisive influence on the training-related sarcoplasmic muscle growth. Because 1g glycogen binds 3g water. The increased water binding in the muscle in turn increases the muscle volume and thus the cross-section. Sarcoplasmic muscle growth is primarily achieved through metabolic exhaustion of the muscle.

The underlying mechanism, which leads to sarcoplasmic hypertrophy, is also known in training science under the term energy deficiency theory.

Summary: In sarcomere hypertrophy, muscle growth occurs through the multiplication of sarcomeres, and in sarcoplasmic hypertrophy, the muscle cross-section increases due to the expansion of the extracellular matrix.


Hyperplasia is the increase in the number of muscle fibers. Theoretically, hyperplasia could also contribute to an enlarged muscle cross-section. An increase in muscle fibers due to training has not yet been proven in humans. Only a few animal experiments have shown that hyperplasia is possible in living animals.

Morphological versus neural adaptation

When it comes to strength training, beginners can quickly expect significant increases in performance. However, especially at the beginning, these are not (yet) due to muscle growth. Increases in strength in the first 6 weeks of strength training are primarily due to neural improvements. Only then was it possible to demonstrate visible morphological muscle growth in scientific studies using MRI.

Factors influencing muscle growth

Whether the targeted muscle growth actually succeeds unfortunately not only depends on structured training and a balanced diet. Ultimately, factors that cannot be influenced, such as genetics, also play a decisive role.

Genetically determined muscle fiber spectrum

To understand the basics of muscular hypertrophy, it is important to understand that there are different types of muscle fibers. Because these are differently suitable for muscle growth.

Muscle fibers are generally classified into two fiber types: Type I and Type II.

Type I fibers, often referred to as slow-twitch fibers, contain a high proportion of myoglobin and are heavily capillarized - that is, with fine blood vessels running through them. They therefore appear red under the electron microscope. This is where the term “red” muscles comes from. These muscle fibers are fatigue-resistant and therefore predestined for activities that require local muscular endurance. However, these muscle fibers are not very fast and cannot exert great force.

Type II fibers, also known as fast-twitch fibers, are less capillary and contain less myoglobin. Accordingly, they appear white in the light microscope representation. This type of fiber is therefore also referred to as “white” muscles. Type II fibers reach significantly higher peak voltages and are faster than type I fibers. This makes them ideally suited to requirements related to strength and rapid strength. However, they tire quickly and are therefore only partially able to carry out activities that require high muscular endurance.

There is also a hybrid of these two muscle fiber types. This is also known as the intermediary type. In the literature, there is sometimes a differentiation between type IIa (intermediate) and type IIb (twitching very quickly).

The proportion of type I and type II fibers is primarily genetically determined. On average, human muscles contain roughly the same amount of type I and type II fibers. Some individuals, especially long distance runners, often have a higher percentage of Type I fibers. Sprinters, on the other hand, have primarily type II fibers. In addition, certain muscles are predisposed to higher percentages of a certain type of fiber. For example, the calf muscle m. Soleus contains on average more than 80% type I fibers. The upper arm muscle m. Triceps brachii, on the other hand, contains an average of around 60% type II fibers.

The growth capacity of type II fibers is significantly greater than that of type I fibers. People who genetically have a higher proportion of Type II fibers therefore have a higher potential for muscle growth.


Hormones also affect muscle growth. The balance of muscle proteins is influenced in part by the neuro-endocrine system. Various hormones have been shown to alter the dynamic balance between anabolic (building) and catabolic (breaking down) stimuli in the muscle and thus control an increase or decrease in muscle protein.


Testosterone is a steroid hormone made from cholesterol. Testosterone has a strong anabolic (muscle mass building) effect. Testosterone's anabolic effects have been attributed in part to its ability to increase protein synthesis and inhibit the breakdown of proteins. Men have about 10 times more testosterone than women. This is believed, in part, to be the main cause of the gender differences in muscle strength and mass.

Insulin-like growth factor 1 (IGF-1)

IGF-1 is a homologous peptide that has structural similarities to insulin. IGF-1 carries out intracellular signal transmission through several signaling pathways. These signal cascades have both anabolic and anti-catabolic effects on the muscles and thus promote increased tissue growth and suppress muscle breakdown.


Insulin is a peptide hormone that is released from the beta cells of the Langerhans cells in the pancreas. Insulin regulates glucose metabolism by enabling the storage of glucose in the form of glycogen in muscle and liver tissue. But insulin also has anabolic effects. Despite this property, the greater influence of insulin on training-related muscle growth is probably primarily due to the inhibition of protein breakdown.


Muscular hypertrophy is already possible in childhood and adolescence. Especially in adolescence, the ability to build muscle mass increases rapidly, especially in boys. This is due to the rising levels of testosterone.

Muscle mass peaks in humans between the ages of 20 and 40. After that, the body loses about 0.5% of its muscle mass per year. From the age of 50 even 1-2% per year. Type II fibers in particular are affected by this. Regular strength training can, however, reduce muscle wasting in older people and even lead to muscle growth.


On average, women have less muscle mass than men - both in absolute and relative terms, based on body weight. The main reasons for this are hormonal differences. The already mentioned testosterone plays the biggest role here.

The optimal training for muscle building

Mechanical tension is one of the most important aspects of exercise-induced hypertrophy. Mechanosensors are sensitive to the intensity as well as the duration of the mechanical load. Metabolic stress can send intracellular signals directly, which in turn provoke hypertrophic adaptations. In order to generate a stimulus that is effective for training, the exercise intensity must be high enough. Thus, only strength training is possible for targeted muscle building. The training control in strength training takes place via the load normative intensity, extent, density and frequency.

Intensity in muscle building training

Training intensity is one of the most important factors in strength training. In order to induce muscle building, targeted strength training in certain intensity ranges is required. In practice, the intensity is usually expressed in relation to the one-repetition maximum (one-repetition maximum / 1-RM). 100% of the maximum repetition corresponds to the weight that can be brought to the high distance exactly once. Classically, weights in the range between 60% and 80% of the repetition maximum are moved to induce muscle growth. In these intensity ranges, 8 to 15 repetitions are usually achieved until the muscle is exhausted.

At very high intensities (> 90% 1-RM), more neurophysiological adaptations are caused; however, the effect on muscle growth is no longer as great.

Higher repetitions (> 15) with lower intensities lead to higher metabolic stress and thus presumably induce higher sarcoplasmic hypertrophy, but lower contractile hypertrophy. The intensity range between 60-80% 1-RM therefore seems to represent the optimal combination of mechanical tension and metabolic stress.

Scope of training in muscle building training

The training scope refers to the number of repetitions in a certain period or in a series. Basically, a higher amount of exercise correlates with higher muscle growth - at least to a certain extent. Ultimately, this in turn depends on the level of performance and training experience.

For beginners, one exercise per muscle (group) per training unit is sometimes sufficient to achieve a training-effective stimulus. This type of training is also referred to as one-sentence training (see operational training or multi-sentence training). For advanced users, it is recommended to do 3 series per muscle group. With 6 or more series per muscle, no further benefit in terms of additional hypertrophy effects can usually be observed. For very ambitious athletes who complete 4 or more training units per week, split training can also be useful, in which several different exercises are performed for each muscle.

For muscle building training it is important that the exercises are carried out up to the exhaustion-related task - true to the motto: "No pain, no gain". We therefore recommend that you do not set strict guidelines for the number of repetitions, but actually perform as many repetitions as possible. Ultimately, the number of repetitions depends on the weight to be moved. The number of repetitions is only logged after the execution for later training analysis.

Stimulus density during muscle building training

The load or stimulus density is the chronological sequence of individual exercises or series. The break between the series should be around 3 minutes (a worthwhile break) so that the muscle can refill itself with high-energy phosphates before the next exercise. If two exercises with different muscle groups follow one another, the break can also be shorter.

The use of supersets can be a means of consciously metabolizing the muscle. For targeted muscle growth, however, the worthwhile break should be observed.

Training frequency in muscle building training

The training frequency refers to the number of training units that are carried out in a certain period of time, usually a week. In order to take advantage of the supercompensation effect, strength training should take place at least twice a week with at least 3-4 days off between training units to achieve a muscle cross-sectional increase. The higher the performance level, the faster the muscle regenerates - so the next training stimulus can then also occur faster (after 2 days).

Quality of movement execution

The quality of the movement execution is not part of the load norms, but it is essential for the execution of the training. It states whether an exercise is being carried out technically flawlessly or according to the instructions of the trainer. Especially with training beginners, it is important to ensure that the exercise is carried out in a technically clean manner. This is not only important for the prevention of injuries, but also for the effectiveness of the training. Because the target muscle is not optimally addressed by an unclean technique or by evasive movements during the exercises, which reduces the training effect.

Exercise selection in muscle building training

To ensure long-term adaptation, a variety of exercises should be used in the course of a periodic training program.

The choice of exercise largely determines how isolated a muscle is addressed. From a functional point of view, it is certainly advisable to choose complex exercises for entire muscle chains. From the point of view of muscle growth, on the other hand, the stress of an exercise on a certain muscle can be estimated the more isolated it is addressed.

In order to take functional aspects into account as well as to include the training of stabilizing muscles, a varied mix of exercises should be planned. The exercise selection should consist of exercises with free weights and machine-guided exercises, as well as single and multi-joint exercises.

How the muscles work in muscle building training

There are three basic types of muscle action:

  • positive dynamic (concentric work) overcoming
  • negative dynamic (eccentric work) yielding
  • static, holding (static work)

How the muscles work

The amount of force that can be arbitrarily generated is eccentric by approx. 20% to 50% higher than concentrically. As a result, a higher load can be placed on the muscle during training with eccentric exercises. In addition, the mechanical stress on the muscle is greatest in the eccentric phase. The higher mechanical tension per active fiber is probably due to a reversal of Hennemann's order of magnitude principle. With eccentric movements, type II fibers are selectively recruited at the expense of type I fibers. Due to the higher load on the type II fibers in the eccentric phase, the extent of the muscular damage to these fibers is increased. This mechanism is believed to have the hypertrophic advantage of eccentric movements.

In practice, however, it is hardly possible to perform purely eccentric exercises. This is almost only possible with machine-controlled devices such as isokinets, which are rarely available.One possibility to support the eccentric phase in strength training is the method of forced reps, in which a training partner supports the movement in the concentric phase, but the eccentric movement is carried out by the person exercising alone without support. This usually allows 2-3 more repetitions to be performed.

Movement speed in muscle building training

The speed of movement in strength training is usually given with three values ​​(given in seconds).

Example: 2/0/2

  • The first value describes the duration of the eccentric movement phase.
  • The second value describes the duration of the static holding phase.
  • The third value describes the duration of the concentric movement phase.

Note: Depending on the literature, the order can also be specified the other way around.

Depending on the extent of movement and exercise, the movement speed of 2/0/2 represents a classic speed for orientation in strength training. Due to the very high intensities, fast movement is not possible anyway. The pace of movement in the concentric phase will slow down, especially as fatigue progresses.

In hypertrophy training, the eccentric phase can also be emphasized, since, according to the theory of mechanical repair, the splicing of the myofibrils takes place primarily in the eccentric phase. Movement speeds of 3/0/2 or even 4/0/2 are sometimes used. On the one hand, this increases the duration of the load in the eccentric phase, while the intensity of the load decreases due to the slower pace of movement. Whether a slower movement in the eccentric phase actually results in a hypertrophic advantage has not yet been scientifically clarified and is questionable.

Range of motion in muscle building training

The range of motion (ROM) describes the range of oscillation with which the movements are carried out. When comparing partial and full ROMs, the benefit in terms of muscle growth benefits is on the part of the full ROM. Nevertheless, the use of so-called partial reps can also be used to vary the training process.

Exercise sequence in muscle building training

Current recommendations for strength training call for large muscle and multi-joint exercises to be performed at an early stage in training. Only then should small muscle and joint exercises be performed. These recommendations are based on the assumption that the performance of multi-joint exercises will be affected if the smaller synergists are already fatigued from previous exercises. Even if this has not been scientifically clarified, adhering to this order makes perfect sense from an injury prophylactic point of view.

If you want to prioritize muscle growth in a certain muscle, it would make sense to train this at the beginning of the training. Because for the maximum number of repetitions, not only the local fatigue is relevant, but also the central nervous. This will increase with the duration of the training and reduce the maximum number of repetitions. In order to stimulate the target muscle as intensively as possible, the highest possible number of repetitions should be performed, which is only possible at the beginning of the training.

Summary of the section

The classic training to achieve maximum muscle building effects should be designed as follows:

  • Intensity: 60-80% RM
  • Scope: 3 sets per exercise (and muscle or muscle group)
  • Breaks: at least 3 minutes between the series
  • Frequency: 2-3x per week
  • Exercise selection: different exercises
  • Working method: if possible, focus on the eccentric phase
  • Movement speed: 2/0/2 (optional: 3/0/2 with focus on eccentric)
  • Range of motion: use full ROM
  • Exercise order: from complex to simple, prioritized muscle at the beginning

Training plan for building muscle

Strength training must be planned systematically so that muscle building can be carried out optimally. A training plan helps here. The training plan specifies how the strength training should be structured so that it leads to the desired success.

In a training plan for targeted strength training to build muscle, exercises are recorded with details of the repetitions and weights that are to be carried out as planned during the training. In addition, the frequency of strength training should be recorded in the training plan so that sufficient training breaks are taken so that the trained muscles can regenerate.

Free training plan templates for building muscle

At the beginning of strength training, success in terms of strength gains or muscle building can be achieved quickly. The more trained the athlete is, the more variations must be built into the training concept. After a while, the body adapts to certain loads during training so that performance no longer increases. A long-term increase in performance can be achieved by varying the load (periodization).

Ideally, the training methods are changed every 3 - 10 weeks. The more advanced the athlete or the higher the performance, the shorter the phases should be. However, not all exercises have to be changed in every cycle; Especially for beginners, a change in the intensity of exercise and thus the repetition range is sufficient.

We are happy to provide training plan templates free of charge below:

Training History Analysis - Free Template

A training plan is not only used to plan the training. Using the training plan and a systematic training log, you can also track the methods with which successes have been achieved or when stagnation has occurred. For this purpose, a training course analysis is carried out in which the results of regular performance tests are recorded. In strength training, the repetition maximum (1-RM) is suitable, which tells you how high the weight is that can just be brought to the high distance.

A free template for a training course analysis to log the training is available for download here:

Diet for building muscle

Diet has a major impact on success in building muscle. With an inadequate diet, in fact no muscle building can take place.

Energy balance

The energy balance, the result between energy consumption and energy requirement, has a decisive influence on the ability to build muscles.

A negative energy balance prevails when the energy consumption is less than the energy demand. This condition leads to catabolism, i.e. a phase in which the body breaks down the body's own energy-rich substances. Muscle growth is not possible with a negative energy balance.

A balanced energy balance is also suboptimal for muscle growth. Because even if the energy consumption and demand are balanced over a certain period of time, there will be phases in which an energy deficit prevails.

The body needs to be in an anabolic phase for muscle growth to be stimulated. This can only be achieved if a positive energy balance prevails over the long term. The energy consumption must therefore be constantly higher than the energy requirement. The combination of strength training with excess energy increases the anabolic effect.

Compared to trained people, untrained people benefit from higher energy surpluses. Untrained people benefit in terms of muscle growth with excess energy of up to 2,000 kcal per day. For those who have been trained, on the other hand, surpluses of 500-1,000 kcal per day are sufficient. The reasons for the differences are presumably that untrained people deal “less economically” with the available energy sources, these have a higher hypertrophic potential and a faster rate of muscle growth.

Macronutrient distribution

Simply looking at the energy balance is not sufficient. Because the body not only needs energy for muscle protein synthesis, but also the “right building blocks”.

Muscle tissue consists primarily of proteins - that is, proteins. It is therefore obvious that the amount of protein ingested has a decisive influence on the build-up of muscle mass (see "The role of proteins in nutrition"). The DGE recommends a daily protein intake of 0.8 grams of protein per kilogram of body weight for adults with light physical work. Athletes have a higher protein requirement. This is around 1.4 to 1.7 g / kg / day. The optimal amount of protein consumed each day ultimately depends on both the energy balance and body composition.

Carbohydrates are made up of carbon, hydrogen and oxygen. The energy that muscles need when exercising comes from ATP, which is primarily obtained from carbohydrates. Even if carbohydrates can be synthesized from proteins via gluconeogenesis, a deficiency is certainly an obstacle to high performance in strength training. A low intake of carbohydrates is apparently sufficient for the performance of strength performance. It should be noted, however, that the brain primarily relies on glucose as an energy supplier and requires around 120 g per day. However, this amount can also be provided via gluconeogenesis.

So far there are no well-founded statements about the optimal amount of carbohydrates that should be consumed in order to induce the best possible hypertrophy effects. The daily intake of 3-7 g / kg body weight can be taken as a rough guide. The range of this recommendation is of course very wide; however, the individual needs are probably also very different.

Fat is the most energetic nutrient. And our depot fat is the largest energy store in the body. Fats serve as cushions for moving organs and are an indispensable building material for our cell membranes.

Despite the great importance of fats for the organism, the influence of fat intake on muscle growth is minimal. However, fat consumption has an influence on testosterone synthesis, so that there is an indirect influence. Omega-3 fatty acids also increase cell membrane fluidity, which could also have a positive effect on protein metabolism.

According to the DGE recommendations, about 30% of the total energy intake should come from fats. The saturated fatty acids and trans fatty acids should be consumed in small amounts, as they have a negative effect on the blood fat values.

Most intake recommendations for athletes are usually based on a specific specification of the amount of protein and / or carbohydrate. The amount of fat to be absorbed ultimately results from this information. This applies to athletes Rule of thumb 1 g fat per kilogram per day. There is room for maneuver upwards and downwards, but care should be taken that with a lower intake, not too few essential fatty acids and fat-soluble vitamins are absorbed.

In order to be able to guarantee the optimal supply of nutrients for your muscle building, you should deal with food science. How many carbohydrates, proteins and fats are contained in which foods and which are particularly suitable for strength athletes, you can find out in our nutritionist training.

Nutrient timing

In addition to the amount of macronutrients, the time of intake is also relevant. One also speaks of nutrient timing. Especially immediately after training - up to about 2-3 hours later - the body is in an anabolic window, in which the supply of carbohydrates and proteins is important in order to stimulate muscle building.

Muscle protein synthesis should be maximally stimulated through the availability of amino acids and the simultaneously stimulated release of insulin through the carbohydrates. 45-75g of carbohydrates and around 15-25g of protein are recommended. A positive side effect of the simultaneous supply of carbohydrates is that the empty glycogen stores are replenished.

In addition, the supply of proteins should be as continuous as possible so that muscle anabolism is stimulated and muscle catabolism is inhibited. The anabolic effects of a high-protein meal last for about 5-6 hours. From this it can be deduced that meals should be taken at these intervals so that the proteins are consistently available to the organism and the body is constantly in the anabolic phase.

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