Muscle fibers

Geschatte leestijd: 15 minuten In this article, I delve into the various muscle fiber and body types. Why will some never become muscular while others, so to speak, grow just by looking at a dumbbell? What makes a body suitable for powerlifting but less suitable for bodybuilding? How come some are naturally good sprinters and others more suited for the marathon? Why can some devour a BigMac menu three times a day without gaining weight while others gain kilos just by peeling a banana? The answer to these questions can be found, among other things, in the various muscle fiber types and the ratio in which they occur in different body types.

Muscle Fiber Types

In the previous parts, I have consistently talked about muscle fibers, or muscle cells, in general. However, muscle fibers can be divided into different types, the most important distinction being: Fast twitch and slow twitch. In the past, three different muscle fibers were sometimes mentioned, but it is now clear that there are two types, one of which can be subdivided into two subcategories. The main difference between these different muscle fibers is the speed at which they can be activated, the endurance, and for which activities they are therefore suitable. The muscles have so-called slow twitch fibers (type I) and fast twitch fibers (type II). The fast twitch fibers can then be subdivided into very fast fibers (type IIb) and moderately fast fibers (type IIa). The type I muscle fibers are also called the red fibers because they look red, while the type II fibers look lighter and are therefore called the white fibers. In the image next to this text, you can see a cross-section of a muscle bundle in which the color difference is clearly visible. In part I, I discussed the different energy systems of muscles. All three systems use ATP (adenosine triphosphate) as an energy source. The main difference in the way a muscle gets energy is whether oxygen is used to convert carbohydrates, fats, and proteins into ATP (with or without the formation of lactic acid) or if the muscle uses the stored ATP supply. In the first case, the muscle can remain active for a long(er) time, but with limited intensity. In the latter case, the muscle can generate much more and explosive power, but for a shorter duration. This difference in energy system and associated functionality is found in the different muscle fiber types. Want to know more about the different energy systems of the body? These energy systems are all described in separate articles. 1. The phosphagen system or ATP-CP system 2. The anaerobic system or lactic acid system 3. The aerobic oxygen system

Slow twitch muscle fibers

Slow twitch muscle fibers, type I, contain many mitochondria, the energy powerhouses of a muscle cell. In addition, they contain many capillaries, literally blood vessels with the thickness of a hair, in this case even thinner. Finally, they contain more myoglobin. All of this works in the aerobic energy system in which oxygen is used. You can compare the red, slow muscle fibers to a steam locomotive. They need a lot of coal and oxygen for combustion to generate the real source of energy, namely steam. As long as you keep shoveling in the coal, the train can keep running. You can see the mitochondria as the oven. Carbohydrates, fats, and proteins can be seen as the coal. Myoglobin is a protein to which oxygen is bound, so logically you can compare it to the necessary oxygen in the oven. The high iron content in myoglobin is the cause of the red color of these fibers. Slow muscle fibers have the smallest diameter. So, slow twitch muscle fibers have the advantage of having many powerhouses. The disadvantage, however, is just like with the train that they do not start quickly, in fact, they will never go fast. This is because they have a low contraction speed. They are therefore suitable for low intensity over a long duration.

Fast twitch muscle fibers, type IIa and IIb

The fast fibers, fast twitch, are divided into type IIa and type IIb (also called x).

Type IIb, “Fast glycolytic fibers”

If a slow twitch fiber is a steam locomotive, then type IIb is a drag racer that can run 400 meters on rocket fuel, but then very fast. These muscle fibers have a lot of glycogen and can split ATP much faster, releasing energy. However, they have fewer mitochondria, capillaries, and mitochondria to produce new ATP. The contraction speed is 10 times faster than that of type I muscle fibers, making the fibers faster and stronger, but for a short duration. Fast muscle fibers have the thickest diameter. Type IIb fibers have a high activity of the enzyme ATPase (see part I). This enzyme, with the help of magnesium, splits ATP. The high activity of this enzyme ensures that the ATP can be split faster. Sprinters, but also powerlifters, make use of these fibers.

Type IIa, “Fast oxidative fibers”

Type IIa fibers are an intermediate form. They contain a lot of mitochondria, capillaries, and myoglobin, and they are able to split ATP quickly. These fibers fall between type I and type IIb in terms of speed and endurance (about 5 times as fast as slow fibers). These are the muscle fibers that bodybuilders often use.

Chickens and Turkeys, White Meat and Red Meat

Often, chickens and turkeys are given as an example of the red and white color of different fibers. The breasts of chickens and turkeys are white while the meat of the legs is much redder. They use their legs all day so these must have a lot of endurance. These therefore have many type I fibers with a lot of myoglobin, making them red. The breast muscles move the wings that are much less frequently used in this poultry. When they are used, it is for a short duration and explosively. Think of the short flight to flee. The breast therefore contains more type II muscle fibers, making it white.

Ratio between fast and slow twitch

Athletic abilities depend on talent and effort. Depending on the sport, talent is largely determined by the ratio of fast and slow muscle fibers in the muscles. There are large differences in the total ratio between fast and slow muscle fibers between people. On average, this is 50%-50% to 60%-40%, with 60% being fast fibers. However, in top sprinters, you see that they have more than 80%, sometimes even 90%, fast muscle fibers, especially in the legs. This has also been studied in the famous sprinter Colin Jackson. In the video below, you can see how a biopsy was taken from his muscle tissue for this purpose. It turned out that he had 25% IIB muscle fibers in his quadriceps, where this is on average 2%! Marathon runners, on the other hand, have very many slow muscle fibers. The more explosive the nature of the sport, the more you benefit from a high number of fast muscle fibers. The more the sport focuses on endurance and stamina, the more you benefit from high numbers of slow muscle fibers. The difference in diameter of the muscle fiber (the thickness) partly explains why a sprinter is much more muscular than a marathon runner. In addition, the ratio differs per muscle (group) depending on the function. The exact ratios per person are also different. However, you will often see that muscles that often have to work for a long time, at relatively low intensity, contain proportionally many slow muscle fibers (such as the posterior neck muscles that hold your head up all day). Muscles that are specifically aimed at short duration high intensity, such as the arms, on the other hand, have proportionally many fast muscle fibers.

“Switching between twitching?”

Let’s say: You were born with very many slow muscle fibers and could therefore become an excellent marathon runner, triathlete, long-distance swimmer, or cyclist. You also have the body that goes with it, thin and dry. Problem: Since you once saw a bodybuilder, you dream of a large muscular body. Can you somehow change the ratio between fast and slow muscle fibers? Yes, but only to a limited extent. First of all, it is useful to know that especially the type IIa fibers are suitable for the most common training methods of bodybuilding. The number of repetitions is often around eight to ten, which is not short enough for the ATP stocks of type IIb fibers. A lot of power is generated, but not super explosively or only one to three repetitions as powerlifters often do.

Diverse studies have shown that type IIb fibers can change into type IIa and vice versa.

One of the studies that demonstrated this was conducted by researchers at the Aristotle University of Thessaloniki in Greece. They compared the muscle fibers of 8 bodybuilders with those of physical education students. They observed that experienced bodybuilders hardly had any type IIb fibers while they had more type IIa fibers than the students. This suggests that the type IIb fibers have changed into type IIa. Other researchers observed a similar change in paralyzed individuals, but in the opposite direction. The paralyzed individuals had much fewer type IIa than type IIb fibers. It is believed that the cause lies in the need for efficiency. The type IIb fibers are historically meant for, for example, fleeing from a saber-toothed tiger or mammoth, or fighting those troublesome Neanderthals who hadn’t realized yet that they were the weaker species. For very short moments. Because they were active the rest of the day, but with lower intensity (walking long distances), it was much more efficient to have more type IIa (and type I) than type IIb. Researchers who look at people leading a sedentary life see the opposite. Not as extreme as the paralyzed individuals, but the couch potatoes and office workers. Because they move little, there is, just like with the paralyzed individuals, little reason for the muscle fibers to work efficiently. In those cases, you also see few of the type IIa fibers and more of the (faster but, in terms of energy, less efficient) type IIb.

Overshoot Principle

Danish researchers observed that muscles whose fibers have changed from type IIb to type IIa due to strength training can change back to type IIb fibers. The men they studied went from 9% type IIb to 2%. The researchers expected that when training stopped, this would increase again to 9%. To their surprise, however, this increased to 18% in the three months when no more training was done. They did not measure after this, but suspected that this would later decrease again (initially, however, they also did not expect it to rise above 9%, so it remains to be seen if this actually happened). Sprinters and other athletes in explosive disciplines already use this overshoot principle, usually without knowing why it works. They know from experience that they sometimes perform better if they train at lower intensity before a competition. Often the fact that this can work was attributed to the rest itself. Now we know that the number of fibers important for them increases due to that rest.

“You Can’t Make a Silk Purse Out of a Sow’s Ear”

The same applies to the predisposition for certain sports. There have been no convincing studies showing that a type I fiber can change into a type II fiber and vice versa. So if you naturally have 80% type I fibers and 20% type II, of which 10% type IIa and 10% type IIb, then you can only influence 10%. So if you’re “born a marathon runner” but want to become a successful sprinter or bodybuilder, it’s very unlikely to happen. Tough luck. This also doesn’t mean that people with similar fiber ratios will perform the same. This is just one of the factors of success. Especially the nervous system ensures, for example, that the control of the fibers happens quickly or slowly. By repeating a lot, you improve this control, allowing you to perform better than someone who has a “better” fiber ratio than you but is not trained. In this respect, see the brain-muscle connection via the central nervous system as the driver of the car and the muscle fibers as the car. Was it Michael Schumacher who was so good or his Ferrari? At the top, however, everyone is well trained, and the natural differences become increasingly important.

Different Body Types or Somatotypes

Many are familiar with the body types ectomorph, mesomorph, and endomorph. These terms have also been mentioned regularly on this site. However, most people think that these body types were determined by looking at physical characteristics such as total body fat amount and its distribution across the body, total muscle mass and its distribution, and body structure with the aim of adjusting training and diet accordingly. Few know, however, that these classifications were established by a psychologist who wanted to demonstrate a connection between human dimensions and character. American psychologist William Herbert Sheldon took thousands of nude photos of students from renowned universities like Yale, Princeton, and Vassar in the 1940s. He classified them into 88 categories of body type and grouped these into the three now famous somatotypes ecto-, meso-, and endomorph. Sheldon thought he could link body types via a numerical system to behavior. His photos caused scandals decades later when some of them suddenly appeared at Yale University and were quickly shredded and burned to prevent possibly famous and/or high-ranking individuals from being recognized in their full glory. His theory about body dimensions and behavior has been largely rejected by modern science. The body types, or somatotypes, are still used, funny enough, but for very different purposes.

Numerical Classification of Somatotypes

Sheldon gave everyone a three-digit number representing his/her somatotype. Very few people will be a primary somatotype. That means they are not 100% ecto-, meso-, or endomorph but fall somewhere in between or even have all three traits. The first number stands for the degree to which you are endomorphic. The second for the degree to which you are mesomorphic and the third for the degree to which you are ectomorphic. This degree is expressed with a number from 1 to 7. Seven means you have all the traits of that somatotype. In the image above, you can see the numerical classification in the top right corner. In total, there are theoretically 343 possibilities (7x7x7), although in practice, someone can never be fully ectomorphic, mesomorphic, and endomorphic. Sheldon attached a psychological profile to each number. Nowadays, this is used more to assess your physical capabilities. The image shows only examples. Not every sumo wrestler is a “632”. Some are thin while there are also fat models. It is only for illustration of the type of body you can approximately imagine with a somatotype.

Which Body Type and What Training and Diet “Goes with It?”

The idea behind linking body type to character (also called “body reading”) is that you could see from someone’s body what kind of life he/she has led. Does someone walk bent over from a lifetime of hard work? Are the shoulders pulled forward from years of work on a PC? Nice idea, but this entire website is based on the science that you can build your own body, model it according to your own insight based on your own potential. With an hour of training a day, I can make the effects on my body of the rest of the day totally invisible. You can have a sedentary job that would make you fat, but by doing strength training and cardio several times a week, you can still look athletic. What does your body say about your character or life at that moment? That you have an active job or do a lot of sports? Today, we use these types in reverse. Not as an indication of your life and/or character based on the effects on your body, but we assume your natural body as it looks with “normal food and activity.” This is important because you have to adjust the training and diet accordingly. Try to estimate for yourself which category you fall into. I will discuss the properties per type, but also indicate to what extent you can adjust your training and diet per type.

Muscle Fibers per Body Type

We have read above that, for example, marathon runners have many type I muscle fibers. In appearance, you could classify these as ectomorphs. Endomorphs often have proportionally many type II(B) fibers in the legs, but fewer in the arms. Based on someone’s physique, you can make a reasonable estimate of their muscle fiber ratios and adjust training accordingly.

Ectomorph, the skinny ruler

• Thin and hard
• Small frame. Thin, light bones.
• Weaker and thinner joints.
• Difficult to gain weight
• Flat chest
• Narrow shoulders due to narrow clavicles.
• Dry muscle mass, very low body fat percentage
• Very fast digestion
• Many type I muscle fibers
• Long muscle bellies

Ectomorphs can often eat whatever they want without gaining weight. For many people, this is an enviable position, but for ectos who really want to build muscle, this means they have to eat relatively more. This can mean hundreds of extra calories compared to, for example, a mesomorph. The advantage is that they almost always stay lean and hardly ever need to “cut” (lose weight while retaining muscle mass). For example, ectos should consider consuming not only protein but also carbohydrates before bedtime. Whereas others may become thicker as a result, for ectos, it is necessary to avoid catabolism (breakdown of muscle proteins for energy) at night. As bodybuilders, ectomorphs can be very successful (although they are often “ecto-mesos” rather than pure ectos). It may take a very long time for them to gain muscle mass, but when they do, they often look more impressive than others. Because they have a very narrow waist, the so-called X-frame is much more prominent. You can clearly see the torso widening from a narrow waist to a broad chest and shoulders. Due to the thin wrists and elbows, the upper and lower arms also appear much larger. Someone like Jay Cutler has a fairly wide waist and therefore needs to be incredibly large on top for a nice X-frame. Guys like current Mr. Olympia Phil Heath (“I finally look big in regular clothes too”), Dexter Jackson, and Toney Freeman all have such narrow waists. The Dutch Ghanaian William Bonac, who recently competed in his first Mr. Olympia, is also a good example of this.

Mesomorph, “ideal” for bodybuilding

• • Athletic
  • Relatively tall
  • Good muscle definition due to relatively large muscle mass, relatively low body fat percentage
  • Strong
  • Gains muscle mass easily
  • Gains fat faster than ectos, but less quickly than endos

Mesomorphs have the “ideal” starting point in bodybuilding. I put “ideal” in quotation marks because it would only be truly perfect if they had the low body fat percentage of ectomorphs. For mesos, the classic “bulk and cut” system applies: first eat enough (calorie surplus) to gain muscle mass and then reduce food intake to decrease the now increased fat mass.

Endomorph

• Soft and round body
• Gains muscle and fat easily
• Relatively short
• Slow digestion
• Difficulty losing fat
• Less well-defined muscles
• Especially strong legs and back

In today’s society, endomorphs have drawn the shortest straw. Fat is a fuel reserve. Nowadays, food in general and carbohydrates in particular are so readily available that there is no need for a body to stockpile as many resources in the reserve tank. Slow digestion is ideal when food is scarce. It is no coincidence that in poorer societies and times (think of the “Rubenesque woman”), thicker people are often considered the ideal compared to societies and times of prosperity. This is not only because their size indicates that they have plenty to eat and are therefore wealthy, but also because it unconsciously indicates that their body is suitable for the circumstances. Nowadays, there is no need for such a fat reserve. Endomorphs need to spend much more time and attention on fat loss in bodybuilding than others. For most, it will be naturally impossible to be both muscular and have a six-pack. Usually, it’s one or the other. Eating enough for muscle mass also means more fat, and reducing food intake to lose fat also means losing a lot of muscle mass for them. However, endomorphs often perform well as powerlifters because they have relatively strong legs and lower back muscles, and body fat percentage (except for weight classes) is less relevant. Just look at the difference in physique between bodybuilders and participants in strongman competitions.

How do you know what type you are?

Based on the mentioned characteristics and shown images, you probably already have a good idea of ​​which type you are. However, extensive measurement methods have been developed for this. The most commonly used is that of Heath and Carter, researchers at the University of San Diego and the University of Pennsylvania. They devised an extensive method that includes, among other things, skinfold measurements, bone and limb dimensions, height, and weight, and determines a somatotype using a complex formula. You can read more about this here and here. A much easier, but certainly less accurate, way is to do tests like this one from bodybuilding.com. Strangely enough, the last question is one about your character, which makes me wonder how they link this to a somatotype and why suddenly Sheldon’s theory comes into play in this regard.

Different training for different body types?

Whether you need to train differently if you have a certain body type to be lean and muscular is a difficult point on which opinions differ. However, these opinions also differ even apart from the different body types. Moreover, certain advice is based on incorrect terminology. One of the most well-known sites about bodybuilding, for example, writes that an ectomorph as a “newbie” should not overtrain. Sorry, but that’s nonsense in practice. As an ectomorph, you can have been training for ten years and have grown significantly. However, you are still an ectomorph in terms of your calorie needs, even if you may look like a mesomorph due to the training. What matters is that you know what is needed to continue growing, and in that regard, as an ectomorph, you still need to eat more than mesos and endos. Formally, somatotyping, classifying by body type, is indeed based on the current body. In practice, however, it is important to realize how you have achieved that appearance and what that says about your natural somatotype. Conversely, as an endomorph, you can be very lean because you have been on a strict diet for years. The fact that you now look like an ecto does not mean that you suddenly need to eat more than others to maintain a normal weight.

Cardio

Where most people agree is on the relative value of cardio. As an endomorph, you should do more cardio than an ectomorph. This is also logical because your goal is primarily to lose fat. As an ectomorph, you often don’t need to do cardio in terms of fat percentage. In fact, you can discourage it because the calories necessary for this cannot be used for muscle growth, so you would have to eat even more. This can also be a pitfall. For example, in my reckless years, I had a period when I worked near a MacDonald’s and literally ate a BigMac menu every day during breaks. As an ecto(-meso), you don’t see anything from that on the outside. However, you’re clogging up nicely on the inside. Later, I was much more conscious about training and deliberately decided not to do cardio to save these calories. It worked great for my muscles, but then I was standing there panting for 10 minutes for a sprint to catch the bus, whereas I used to run long distances. Because your oxygen intake and therefore endurance are also important for your performance, as an ectomorph, you should do cardio, but for your conditioning. This means you need to eat extra food for the calories you burn, whereas for an endomorph, the focus is on burning as many calories as possible. In addition, as an ectomorph, you can choose to have a higher training intensity in terms of cardio, such as aiming for between 80-90 percent of your maximum heart rate instead of the traditional 60-70 percent of the “fat-burning zone.” You can also opt for HI(I)T, High-Intensity (Interval) Training. This type of training focuses more on endurance by increasing the so-called VO2-max, the maximum oxygen intake. There are also many studies showing that this burns more calories and leads to more weight loss. Fun for the endomorph and mesomorph who want to cut, but for the ectomorph, it’s something else to consider in terms of calorie intake.

Strength Training

However, when it comes to strength training, the advice is either less specific or not supported. For example, you often hear a lot of tips for muscle mass for ectomorphs that could apply to everyone. You also hear specific advice on training intensity and volume where a scientific explanation or reference to research is lacking.

References

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