Training - research and science
The influence of muscle fibre distribution on bodybuilding
Probably very few bodybuilders could say that all of their muscle groups respond in exactly the same way to a workout because most people who work out have a few muscle groups that bulk up more quickly, are more powerful than the others, or which develop more quickly. The reason for this phenomenon is in the muscle itself, or rather in the composition of the muscle itself, which is primarily determined by genetics. This means that, in addition to your training programme and other external factors, the structure and composition of your muscles determines whether you will be able to achieve top results in the maximum strength area or not. However, it is virtually impossible to influence the composition of your muscles because this is primarily determined by your genes and is inherited from your parents. In the field of high-performance bodybuilding, it has been shown that the distribution of different types of muscle fibres has a major influence on the extent of the final physical development. The reasons for this will become clear if we take a closer look at the different types of muscle fibre.
Types of muscle fibre
Our muscles mainly consist of huge numbers of individual muscle fibres. However, these fibres are not all the same but can be divided into two major categories depending on their different characteristics.
Type I: Slow-twitch muscle types = ST or tonic type) and type II: fast-twitch muscle types = FT or phasic type). The different contraction characteristics of each muscle fibre type are determined by different molecular structures and different nerval pathways.
The different types of contraction of the individual fibres are indicative of variations in the muscle metabolism. The fast-twitch fibres store more of the rapidly available energy sources such as phosphates and glycogen, while the slow-twitch fibres have a high intracellular fat percentage as well as more mitochondria. The ST and FT fibres also differ when it comes to innervation. FT fibres are controlled by fast-conducting nerve fibres, while ST fibres are controlled by slow-conducting nerve fibres.
In order to develop a truly competition-level body, you not only need the right workout regimen and the right nutrition, but also the right genes - particularly when it comes to muscle composition.
For high strength, it is necessary to have a high amount of fast-twitch muscle fibres; for endurance sport, you need the exact opposite. Only the combination of various training methods enables you to train all muscle fibre types.
The white muscle fibres can then also be divided into the further following categories: type II C, type II A and type II B. The type II C muscle fibres are designated an intermediate type because they can take on the characteristics of a slow-twitch fibre with endurance sport. The other muscle fibres cannot be changed via training, meaning that people who have a high number of ST fibres will not achieve the same results as another person who has a higher number of FT fibres. However, the opposite also applies because for absolute endurance performance capacity, it is necessary to have the required amount of inherited ST muscle fibres. For this reason, world-class athletes in strength and fast-strength disciplines generally have predominantly type II muscle fibres while endurance athletes have type I fibres. For this reason, the distribution of the various muscle fibre types is not the same for every muscle but can vary significantly from muscle group to muscle group.
Muscle fibre distribution and bodybuilding
The majority of the population has roughly the same percentages of fast and slow-twitch muscle fibres. However, in individual cases, the distribution can be 90:10 or 10:90. The fast-twitch fibres are already approx. 10–15% larger than slow-twitch fibres, even before they have been exercised. For this reason, it is a big advantage for bodybuilders to have a large number of FT fibres, particularly because they are best adapted to hypertrophy. However, this does not mean that a bodybuilder with predominantly ST muscle fibres cannot achieve significant growth because the ability of each muscle fibre type to bulk up is preprogrammed. In order to achieve the most growth in bodybuilding, these different types of muscle fibre need to be trained in different ways.
Training the various muscle fibre types
In bodybuilding and fitness training, the distinction is made between strength training, hypertrophy training and maximum strength training. Each of these three types of training is geared towards working out each of these different muscle fibre types. Strength training primarily challenges the types I and II C muscle fibres, while maximum strength training challenges the type II B fibres. Although hypertrophy training at 8–12 reps achieves the biggest growth in muscle volume, strength training and maximum strength training are also necessary in order to optimally develop all muscle fibres. The question remains as to how this should be best achieved during the training process. There are two different approaches to this: either you can try to work on all muscle fibres in one workout, or you train with one particular method for a set period of time. If you want to combine all the methods in one training unit, you should complete maximum strength training first with 5–8 reps in order to challenge the fastest type II B muscle fibres. After that, do a few sets of 10–12 reps. You can then round off your workout with two or three sets of around 15–25 reps in order to put sufficient stress on the slower muscle fibres. In practice, this system only brings results after a certain period of time; however, it has been proven that the workout method that is primarily used for a certain period of time can then be made more effective by changing to another method.
Is it possible to change the way a muscle looks?
In the discussion about muscles and muscle fibres, the question often arises as to whether it is possible to change the way a muscle looks with the right exercises. In biceps training, for example, it is often said that barbell curls are good for bulking up while concentration curls increase the height of the biceps muscle.
Even the most precisely thought-out exercises cannot train individual parts of a muscle fibre. The end results for the muscle are primarily determined by your genes.
Using different exercises makes it possible to train certain muscle origins more intensively than others, but in general the whole muscle tenses up -there isn’t really such a thing as a workout to increase the height of the biceps.
The truth is that the final shape of the muscle as well as the muscle fibre distribution is genetically determined. It is true that the way a muscle looks can be changed by training but no one can change the shape of the muscle beyond their predefined genetic limits with exercise. The reason for this is that either the whole muscle fibre tenses up or it doesn’t, thus making it impossible just to train only the front part of the biceps muscle or just the inside sections of the chest muscles. Some athletes would probably respond to this statement by saying that they feel the outer chest muscles when doing wide-grip bench presses and the inner chest muscles more when doing close-grip bench presses. The reason for this is not that the chest muscles are under different amounts of stress but that the wide grip brings the chest muscles into more of a stretch at the lowest point of the movement, which is responsible for the feeling of strain in the outer chest muscles.
That is not to say that only one exercise is needed in order to completely develop a muscle, because it actually possible to increase stress on one or more of the muscle heads for most multi-headed muscles. An example of this is is doing dumbbell extensions behind the head. In this exercise, the long head of the triceps muscle is subjected to higher pre-tension and is therefore put under more stress than in standard cable pulldowns. However, it is not possible to stress individual parts of this muscle head in particular. For the biceps muscle, it is very difficult to stress one of the two parts of the muscle more than the other because the points of insertion of the muscle are located very close to each other.
But even with different stresses on the various muscle heads, you cannot promise yourself any miracles. Try stressing the different muscle fibre types and different muscles with various exercises and numbers of reps in order to achieve the best results. Change the number of reps and types of exercises from time to time in order to vary the stress your muscles are under. Keep in mind that even if you don’t have the ideal muscle fibre composition and muscle shapes for bodybuilding, you can still achieve improved performance. You can only know how far you will get with your physical development when you have continually pushed the boundaries.
Harald Gärtner
