In this third part of the series, I will discuss 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 so for bodybuilding? Why are some naturally good sprinters and others more suited for marathons? Why can some eat three Big Mac meals a day without gaining weight while others gain pounds just by peeling a banana?
The answer to these questions can be found, among other things, in the different types of muscle fibers and the ratio in which they occur in different body types.
Muscle Fiber Types
In the previous parts, I have always 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 divided into two subcategories. The most important difference between these muscle fibers is the speed with which they can be activated, their 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 are further divided into very fast fibers (type IIb) and moderately fast fibers (type IIa). Type I muscle fibers are also called red fibers because they look red, while type II fibers look lighter and are therefore called white fibers. The image alongside shows a cross-section of a muscle bundle where 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 how a muscle obtains energy is whether it uses oxygen to convert carbohydrates, fats, and proteins into ATP (either 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 longer time but at limited intensity. In the latter case, the muscle can generate much more and explosive force but for a shorter duration.
This difference in energy system and associated functionality is reflected in the different muscle fiber types.
Slow Twitch Muscle Fibers
Slow twitch muscle fibers, type I, contain many mitochondria, the powerhouses of a muscle cell. They also contain many capillaries, literally blood vessels as thin as a hair, in this case even thinner. Finally, they contain more myoglobin. All this works in the aerobic energy system where oxygen is used. The red, slow muscle fibers can be compared 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 coal into it, the train can keep running. You can see the mitochondria as the furnace. Carbohydrates, fats, and proteins can be seen as the coal.
Myoglobin is a protein to which oxygen is bound and can thus logically be compared to the necessary oxygen in the furnace. The high iron content in myoglobin causes the red color of these fibers. Slow muscle fibers have the smallest diameter. 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 long duration activities.
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 drive just 400 meters on rocket fuel, but at super speed. 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 create new ATP.
The contraction speed is 10 times as fast as 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 ATP-ase (see part I). This enzyme, with the help of magnesium, splits ATP. The high activity of this enzyme allows ATP to be split faster. Sprinters, as well as powerlifters, use these fibers.
Type IIa, “Fast Oxidative Fibers”
Type IIa fibers are an intermediate form. They contain both a lot of mitochondria, capillaries, and myoglobin and they are capable of splitting ATP quickly. In terms of speed and endurance, these fibers fall between type I and type IIb (about 5 times as fast as slow fibers). These are the muscle fibers that bodybuilders make a lot of use of.
Chickens and Turkeys, White Meat and Red Meat
Chickens and turkeys are often given as examples for the red and white color of the different fibers. The breast of chickens and turkeys is white while the meat of the legs is much redder. The legs are used all day and therefore must have a lot of endurance. They contain many type I fibers with a lot of myoglobin, making them red. The chest muscles move the wings, which in this poultry are used much less often. When they are used, it is for a short duration and explosively. Think of the short flight to escape. The chest contains more type II muscle fibers, making it white.
Ratio Between Fast and Slow Twitch
Athletic capabilities depend on both talent and effort. The talent is, depending on the sport, largely determined by the ratio of fast and slow muscle fibers in the muscles.
There are significant differences in the total ratio between fast and slow muscle fibers among people. On average, this is 50%-50% to 60%-40%, where 60% refers to the 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 was also investigated in the famous sprinter Colin Jackson. In the video below, you 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 the average is 2%!
Marathon runners have a lot of 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 is focused on endurance and stamina, the more you benefit from high numbers of slow muscle fibers. The difference in diameter of the muscle fiber (thickness) partly explains why a sprinter is much more muscular than a marathon runner.
In addition, the ratio varies per muscle (group) depending on the function. Here too, the exact ratios differ per person. 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 focused on short-duration high intensity, such as the arms, have proportionally many fast muscle fibers.
“Switching between Twitching?”
Suppose: You were born with very many slow muscle fibers and could, for example, become an excellent marathon runner, triathlete, long-distance swimmer, or cyclist. You also have the body that goes with it, thin and lean. Problem: Since you saw a bodybuilder once, you dream of a large muscular body. Can you somehow ensure that you change the ratio between fast and slow muscle fibers? Yes, but only to a limited extent.
Firstly, it is useful to know that especially the type IIa fibers are suitable for the most common bodybuilding training forms. The number of repetitions is often around eight to ten, which is not short enough for the ATP supplies of type IIb fibers. A lot of strength is generated, but not super explosive or only one to three repetitions as powerlifters often do.
Various studies have shown that type IIb fibers can change into type IIa and vice versa.
One of the studies that showed this was done by researchers from Aristotle University of Thessaloniki in Greece. They compared the muscle fibers of 8 bodybuilders with those of physical education students. They saw that experienced bodybuilders hardly had type IIb fibers while they had more type IIa fibers than the students. This indicates that the type IIb fibers have changed into type IIa.
Other researchers saw a similar change in paralyzed people, but in the opposite direction. The paralyzed people had much fewer type IIa than type IIb. It is thought that the reason lies in the need for efficiency. The type IIb is historically intended for, for example, fleeing from a saber-toothed tiger or mammoth, or fighting with those pesky Neanderthals who had not yet realized they were the weaker species. For very short moments, therefore. Because people 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.
The opposite is seen by researchers looking at people who lead a sedentary life. Not as extreme as the paralyzed, but the couch potatoes and office workers. Because they move little, there is, as with the paralyzed, 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 saw that muscles whose fibers have changed from type IIb to type IIa through strength training can change back into type IIb fibers. The men they studied went from 9% type IIb to 2%. The researchers expected that when they stopped training, this would rise again to 9%. To their surprise, however, it increased to 18% in the three months in which they no longer trained. They did not measure further, but suspected that this would later drop back (they initially also did not expect it to rise beyond 9% so it is questionable whether this ultimately happened).
Sprinters and other athletes in explosive disciplines already make use of this overshoot principle, usually without knowing why it works. They know from experience that they sometimes perform better if they train at lower intensity prior to a competition. Often, the fact that this can work was attributed to the rest itself. Now it is known that the number of fibers important to them increases due to that rest.
“Who is born a penny will never become a quarter”
The same applies to the talent 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%.
If you are “born a marathon runner” but want to become a successful sprinter or, for example, bodybuilder, it will very likely never work. Yeah, tough luck for you. That does not mean, however, that people with similar fiber ratios will perform the same. This is just one of the success factors. Especially the nervous system ensures, for example, that the control of the fibers happens quickly or slowly. Through a lot of repetition, 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, consider 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? However, at the top, everyone is well-trained, and natural differences weigh more heavily.
Different Body Types or Somatotypes
Many are familiar with the body types ectomorph, mesomorph, and endomorph. These terms have also appeared on this site regularly. Most, however, think these body types were established by looking at physical characteristics such as total body fat and its distribution over the body, total muscle mass and its distribution, and body build with the goal of, for example, adjusting training and diet accordingly. Few know, however, that this classification was established by a psychologist who wanted to demonstrate a link between human dimensions and character.
In the 1940s, the American psychologist William Herbert Sheldon took thousands of nude photos of students from renowned universities such as Yale, Princeton, and Vassar. He categorized them into 88 categories of body type and grouped these into the three, now famous, somatotypes ecto-, meso-, and endomorph.
Sheldon thought to link body types to behavior through a numerical system. His photos caused scandals decades later when some of them suddenly appeared at Yale University and were quickly shredded and burned to prevent, possibly by now famous and/or high-ranking, individuals from being recognized in full glory.
His theory on body dimensions and behavior has been largely rejected by modern science. Interestingly, the body types, or somatotypes, are still used, albeit 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 characteristics of all three.
The first number indicates the extent to which you are endomorphic. The second for the extent to which you are mesomorphic, and the third for the extent to which you are ectomorphic. This extent is expressed with a number from 1 to 7. Seven means that you have all the characteristics of that somatotype. In the image above, you see the numerical classification at the top right. In total, there are theoretically 343 possibilities (7x7x7) although in practice someone can never be completely ectomorph, mesomorph, and endomorph.
Sheldon attached a psychological profile to each number. Nowadays, however, this is more used to assess your physical possibilities. The image only shows examples. Not every sumo wrestler is a “632”. Some are thinner, while there are also fat models. It’s just to illustrate what type of body you can approximately imagine with a somatotype.
Which Body Type and What Training and Nutrition “Belong to It?”
The idea behind linking body type to character (also called “body reading”) is that you could tell what kind of life someone has led by looking at their body. Does someone walk bent over from a lifetime of hard work? Are the shoulders pulled forward by 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 insights based on your own potential. With an hour of training per 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 play a lot of sports?
Nowadays, 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 start from your natural body as it looks with “normal nutrition and activity.” This is important because you need to adjust your training and nutrition accordingly. Try to estimate in which category you fall.
I will discuss the characteristics per type, but also indicate to what extent you can adjust your training and nutrition per type.
Muscle Fibers per Body Type
We have read above that, for example, marathon runners have many type I muscle fibers. Appearance-wise, you would classify them as ectomorph. 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 the training accordingly.
Ectomorph, the skinny one
- Thin and tough
- Small frame. Thin, light bones.
- Weaker and thinner joints.
- Difficult to gain weight
- Flat chest
- Narrow shoulders due to narrow clavicles.
- Lean muscle mass, very low fat percentage
- Very fast metabolism
- 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 the ectos who really want to become muscular, it means they need to eat relatively a lot. This could mean hundreds of calories extra compared to, for example, a mesomorph. The advantage is that they almost always stay lean and almost never need to “cut” (lose fat while maintaining muscle mass). Ectos, for example, would do well to not only take protein but also carbohydrates before sleeping. Where others might get fatter by doing this, it’s necessary for ectos not to catabolize (breakdown of muscle protein for energy) at night.
As bodybuilders, ectomorphs can be very successful (though they are often “ecto-mesos” and not pure ectos). It then takes a long time before they 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 shows much better. You can clearly see the torso widening from a narrow waist to a wide chest and shoulders. Because of the thin wrists and elbow, the upper and lower arms also look much bigger. Someone like Jay Cutler has a pretty wide waist and therefore needs to be huge on top for a nice X-frame. Guys like current Mr. Olympia Phil Heath (“I finally look big in normal clothes too”), Dexter Jackson, and Toney Freeman all have such a narrow waist. 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 fat percentage.
- Strong
- Easily grows muscle mass
- 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 be truly perfect if they had the low fat percentage of ectomorphs. Therefore, the classic “bulk and cut” system applies to mesomorphs: First eat enough (calorie surplus) to gain muscle mass and then reduce food intake to decrease the subsequently increased fat mass.
Endomorph
- Soft and round body
- Easily gains muscle mass and fat
- Relatively short
- Slow metabolism
- Difficulty losing fat
- Less well-defined muscles
- Mainly strong in legs and back
In today’s society, endomorphs have drawn the short straw. Fat is a fuel reserve. Nowadays, food in general and carbohydrates in particular are so easily available that there is no need for a body that throws as many resources as possible into the reserve tank. The slow metabolism is ideal when there is little food. It’s no coincidence that in poorer societies and times (think of the “Rubens woman”), often fatter people are the ideal image than in societies and times where there is prosperity. This is not only because their size indicates that they have enough to eat and are therefore affluent, but also because this unconsciously indicates that their body is suitable for the conditions. Nowadays, there is no more need for such a fat reserve.
In terms of bodybuilding, endomorphs have to spend much more time and attention on losing fat than others. For most, it will be impossible on a natural basis to be both muscular and have a six-pack. Usually, it’s one or the other. Eating enough for muscle mass also immediately means more fat, and reducing food intake to lose fat means for them also a lot of loss of muscle mass. As powerlifters, endomorphs often do well because they have proportionally very strong legs and lower back muscles and fat percentage (except for weight classes) is less relevant. Just look at the difference in physique between bodybuilders and participants in strongest man competitions.
How do you know which type you are?
Based on the mentioned characteristics and shown images, you probably already have a pretty good idea of which type you are. However, extensive measurement methods have been developed for this. The most used is that of Heath and Carter, researchers from the University of San Diego and the University of Pennsylvania. They devised an extensive method where, among other things, skin fold measurements, measurements of bones and limbs, length, and weight are measured and through a complicated formula, a somatotype is determined.
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. Oddly enough, the last question is one about your character, which makes me wonder how they link this to a somatotype and why in this respect suddenly Sheldon’s theory comes into play again.
Different Training for Different Body Types?
Whether you should train differently if you have a certain body type to be lean and muscular is a difficult point about which opinions vary. However, these opinions also vary independently of the different body types. Moreover, certain advice is based on incorrect terminology. One of the most famous bodybuilding sites, for example, writes that an ectomorph as a “newbie” should not overtrain. Sorry, but that’s nonsense in practice. You can have been training as an ectomorph for ten years and have grown significantly. Then you are still an ectomorph in terms of your calorie needs even if you may look like a mesomorph due to the training.
It’s important to know what is needed to continue growing, and in that respect, 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’s important to realize how you got to that appearance and what that says about your natural somatotype. Conversely, as an endomorph, you can be very skinny because you’ve 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 another to be at a normal weight.
Cardio
What most agree on is the relative value of cardio. As an endomorph, you should do more cardio than an ecto. This makes sense because your main goal is to lose fat. As an ecto, you often don’t need to do cardio in terms of fat percentage. In fact, it can be discouraged because the necessary calories can’t be used for muscle growth, so you have to eat even more.
This can also be a pitfall. For example, I had a period in my reckless years when I worked near a McDonald’s and literally ate a Big Mac menu every day during the break. As an ecto(-meso), you don’t see any change in appearance. 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. Worked great for my muscles, but then I was gasping for breath after a sprint to the bus for 10 minutes, whereas I used to run long distances.
Because your oxygen uptake and thus endurance are also important for your performance, as an ecto, you’d better do cardio, but then for your condition. This means that you have to eat extra food for the calories you burn while it’s about burning as many calories as possible for an endomorph. In addition, you can choose as an ecto to be higher in your training intensity in terms of cardio regarding your heart rate (for example, 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 uptake. Also, many studies indicate that you burn more calories and lose more weight with it. Nice for the endomorph and mesomorph who want to cut, for the ectomorph again something to take into account in calorie intake.
Strength Training
However, when it comes to strength training, the advice is either less specific or not substantiated. For example, you hear a lot of tips for ectos for muscle mass that could apply to everyone. You also hear specific advice about training intensity and volume without a scientific explanation or reference to research.
References
- N. Kesidis et al. Myosin heavy chain isoform distribution in single fibers of bodybuilders. Eur J Appl Physiol. 2008 Jul;103(5):579-83. doi: 10.1007/s00421-008-0751-5. Epub 2008 May 7.
- J.L. Anderson et al. Muscle, genes and athletic performance. 2000, Scientific American
- K. Davis. More than a meal: the turkey in history, myth, ritual, and reality. New York, Lantern Books, c2001. 192 p.
- L. Grivetti et al. Food in American history part 2: turkey. Nutrition today, v. 36, March 2001: pg.88-96.
- E. Haseltine. The body electric: measuring your fast-twitch and slow-twitch fibers. Discover, v. 22, Dec., 2001: pg. 92.
- F. Martini. Muscle tissue. Fundamentals of anatomy and physiology, c1998. pg 276-313. (Slow and Fast Fibers, p. 302)Bibliography item 1.
- B. McGinty. The American turkey. Early American life, v. 9, 1978: 24-26, 76-77.
- S. Vogel. Prime mover: a natural history of muscle. New York, W.W. Norton & Company, c2001. 370 p.
- W.H. Sheldon. Correlated Physiques and Traits of Behavior. Headed Research Center”. The New York Times. September 18, 1977
- Imran et al. A Comparative Study of Body Builders and Weight Lifters on Somatotypes. Journal of Education and Practice. 2011, vol.2, no.3
- J. Carter. THE HEATH-CARTER ANTHROPOMETRIC SOMATOTYPE- INSTRUCTION MANUAL -San Diego State University, March 2002
