So, success in strength and aerobic sports, be it bodybuilding, powerlifting, running or something else, largely depends on genetics, and more specifically - on the ratio of fast (white) and slow (red) muscle fibers (MF). It is this genetic predisposition that determines how easy it will be for you to build muscle, increase strength or endurance. Roughly speaking, whether you will become a champion or not. The article will be divided into 2 parts.
Why is this so important? Because different types of activity require different energy sources and, accordingly, involve different types of MF. If your goal is to pump up muscles or become more enduring, you simply need to understand which MF you need to train.
In order not to tire you with repetitions, we will use the abbreviation “MF” to denote muscle fibers.
Now we will figure out what types of MF exist, how they differ from each other. And at the end, I will summarize the results in the form of a table and give specific recommendations for training for each type of MF. After all, understanding these nuances is the key to effective training and achieving the desired results!
- By the way, did you know that even within one type of MV there are subtypes? For example, fast MVs are divided into types IIa and IIb, each of which has its own characteristics in the speed of contraction and resistance to fatigue.
- And another interesting fact: the ratio of fast and slow MVs can change depending on training, but to a very small extent. The main contribution is still made by genetics.
Types of Muscle Fibers: Type 1 and Type 2
Now let’s talk about the types of muscle fibers (MF). There are two main types: type 1 and type 2. But to understand how they differ, let’s first look at what MF are made of:
- Capillaries: Deliver oxygen and nutrients to the muscles, vital elements for their work and growth.
- Endoplasmic (sarcoplasmic) reticulum: Calcium ions are stored here, which are necessary for MF contraction.
- Sarcolemma: This is a connective tissue sheath, a kind of membrane of the muscle cell.
- Nuclei: Control centers, store and distribute information. In one MF there can be from several hundred to several thousand of them!
- Mitochondria: Energy stations of the cell, produce ATP (fuel for muscles). The number of mitochondria in one muscle cell can vary from 50 to 1000 or even more.
- Myofibrils: These are elongated protein threads that provide contraction of the myofibrils. Their length can reach 2-3 cm.
So, the difference between the first and second types of myofibrils lies in their structure and biochemical properties, in particular, in the methods of ATP production (oxidative and glycolytic) and mechanical characteristics (contraction speed, change in length and traction force).
Conventionally speaking, the first type of myofibrils are “marathon runners”, and the second are “sprinters”. They differ in color (red and white) and specialize in different types of load. More about this - below!
Table - main indicators of MV depending on their type
Type 1: Slow Oxidative (SO)
So, type 1 muscles, also called slow oxidative (SO) – are the real marathon runners among muscle fibers. They are not that strong, and contract rather slowly, but they have no shortage of endurance!
Why are they so resilient? It’s all about their structure:
- Firstly, they are red. Do you know why? Because they have a lot of myoglobin – a protein that stores oxygen, like hemoglobin in the blood. And they also have a lot of mitochondria – these are like power plants that produce energy from glucose.
- Secondly, they have an excellent capillary network. This means that a lot of blood constantly flows to them, and with it – oxygen and nutrients.
- Thirdly, they do not require much effort to activate. The motor neuron that controls them is triggered even with a small load. This means that they are the first to start working.
Although they have a lot of myosin (a contractile protein), the enzyme that releases energy for contraction (ATPase) works slower than in fast fibers. That’s why they contract more slowly. Communication with the brain occurs through alpha motor neurons.
In fact, MO fibers are ideal for long, monotonous exercises, such as long-distance running, swimming, or maintaining a certain posture. Imagine how they work when you’re just standing - keeping you upright, preventing you from falling!
By the way, did you know that professional long-distance runners can have up to 90% MO fibers in their legs? This is what allows them to run for hours without getting tired!
Type 2: Fast Glycolytic Fibers
Meet the “sprinters” of the muscle world - fast glycolytic fibers! If slow oxidative (SO) fibers are marathon runners, then these guys are built for short, explosive efforts.
How are they different from SO? In almost every way!
- First, they are thicker and stronger. This is just what you need for lifting weights or sprinting.
- Second, they are white. Why? Because they have few mitochondria, lipids and myoglobin (remember, this is the protein that stores oxygen?). They also have poor blood supply.
- Third, they have a lot of anaerobic oxidation enzymes and myofibrils. This allows them to produce energy very quickly, but not for long. They have less myosin than SO, but it works faster and more efficiently, producing ATP at a crazy speed!
- Fourthly, they have a well-developed sarcoplasmic reticulum, which stores calcium ions (Ca2+). And calcium, as you remember, is necessary for muscle contraction.
- Fifthly, communication with the brain is carried out through large alpha motor neurons.
The main disadvantage of fast glycolytic fibers is that they tire very quickly. They lack oxygen, and they begin to produce energy without it, which leads to the accumulation of lactic acid and fatigue.
In short, fast glycolytic fibers are ideal for short-term high-intensity work.
By the way, these fibers are also divided into subtypes. More on that later!
2a type: Fast Oxidative Glycolytic (GOG)
If we imagined the first two types as a marathon runner and a sprinter, these guys are generalists. They occupy a middle ground between slow and fast fibers, and, as a result, have qualities of both types.
What you need to know about GOG fibers:
- Size: They are of medium thickness. Not as powerful as fast 2b fibers, but not as thin as slow type 1 fibers.
- Fatigue: They tire faster than slow fibers, but slower than fast ones. Pretty logical, right?
- Strength and contraction speed: Everything is in the middle here too.
- Energy: GOG fibers can use both oxidative (with oxygen) and anaerobic (without oxygen) processes to produce ATP. This makes them very flexible and allows them to adapt to different types of loads.
In general, BOG fibers are workhorses that can do a variety of jobs. They are well suited for strength training, moderate-intensity endurance training, and other activities that require a combination of strength and endurance.
You know, these fibers are like good all-around tires for your car. They are not the best for track racing, and they are not the best for off-road driving, but they are great for everyday city driving!
2b type: fast glycolytic fibers (FG)
Fast-twitch, very strong, large muscle fibers that tire easily, while having a high degree of motor neuron activation, that is, in order for the white muscles to start working, it is necessary to apply quite a lot of effort per unit of time, for example, to lift a heavy weight for a short time.
A distinctive feature of fast MF is the low content of mitochondria and their supply of ATP through anaerobic oxidation, i.e. glycogen will serve as the main source of energy supply, so there will be a lot of it in such muscle fibers.
2c type: transitional
Such muscle fibers exhibit both oxidative and glycolytic activity and can switch from one type to another depending on the training program (for general endurance or strength), for example, from type 1 to type 2 or vice versa. There are very few such MF in the human body, about 1%.
Skeletal muscles consist of different types of motor units (MU), which provide the connection of certain muscle groups with the spinal cord, that is, innervation of different types of muscle fibers by a motor neuron occurs, therefore one bundle of muscle fiber can consist in different %-ratio of different types of MU, slow and fast.
2x type
The fastest type of muscle fiber, show the greatest strength, therefore, get tired the fastest. It is not difficult to assume that in such fibers the number of mitochondria will tend to zero, creatine phosphate will act as an energy source, the degree of activation of the motor neuron will be very, very high.
For example, such fibers of the 2x type will be involved when performing strength exercises with maximum and near-maximum weights for 1-2 repetitions.
Fast and Slow Muscle Fibers
This classification of muscle fibers (MF) differs based on the speed of muscle fiber contraction and the activity of the enzyme myosin ATPase (adenosine triphosphatase).
ATPase is an enzyme that provides the rate of adenosine triphosphate (ATP) production. Accordingly, the higher the activity of the ATPase enzyme, the faster ATP is resynthesized in the cell for the production of energy for muscle contraction. Therefore, fast MF have a significantly higher contraction speed and ATPase enzyme activity compared to slow MF, whose myosin has low ATPase activity.
The training process does not affect ATPase activity, as it is genetically determined, meaning the ratio of white and red MF is inherited.
The release of energy from ATP is carried out by ATPase, and one molecule of adenosine triphosphate is only enough for one stroke, or rotation, of the myosin bridges (remember the article on muscle failure, where we talk about muscle contraction; those interested can refer to it). These detach from the actin filaments (microfilaments), returning to their original position, after which they reattach to a section of actin with subsequent stroke execution. It is noteworthy that all single strokes have the same speed for all muscles, and each stroke requires a new molecule of ATP.
In fast (white) muscle fibers, i.e., those in which ATPase has high activity, ATP breakdown occurs faster, and the number of strokes per unit of time increases in fast MF. Consequently, the muscle contraction speed also increases, and it becomes stronger.
Strength sports, as you probably guessed, involve fast muscle fibers, while sports where endurance plays a primary role (track and field, swimming, skiing, soccer, basketball, etc.) utilize slow, or red, MF.
Fairly simple experiments have also been conducted on animals, which prove that the predominance of fast muscle fibers gives an advantage in speed. For example, a Finnish horse with about 70% fast MF in its muscle composition can reach a speed of 12.5 m/s, while another horse (actively used in short-distance races) with a muscle composition of 90% fast MF can reach a speed of 20 m/s.
Thank you for your attention! See you in the second part! Good anabolism to all!