WHAT TYPES OF MUSCLE FIBERS DO YOU HAVE AND WHAT ARE THEY RESPONSIBLE FOR?
The better muscle memory develops under the influence of regular physical activity, the longer a person
remains in good shape and the faster he recovers from illness.
Muscle fibers within the human body are usually classified according to 4 main characteristics. Fibers are
divided into red and white, slow and fast, low-threshold and high-threshold, as well as oxidative,
intermediate and glycolytic. Below we will consider the specifics of each classification separately.
- Red and white
The shade of the muscle fiber is noticeable in its cross-section. It is determined by the concentration in
the sarcoplasm of myoglobin, a specific muscle pigment. At low concentrations, this substance gives
tissues a light pink tint, and at high concentrations, it gives a rich red-brown tint.
The myoglobin content, in turn, depends on the number of mitochondria. The main purpose of this
substance is to transport oxygen from the surface of the muscle fiber to the mitochondria. As a result of
training, the concentration of myoglobin in tissues can increase – accordingly, the fibers tend to darken or
lighten over time.
White fibers use glycogen as energy, and red fibers use triglycerides. The body of sprinters and jumpers is
dominated by white fibers, while the body of long-distance runners is dominated by red fibers.
The color of almost every human muscle is heterogeneous, since it contains fibers of both shades, as well
as tissues with weak pigmentation.
- Slow and fast
Fibers with high ATP activity are called fast fibers. ATP in this case stands for adenosine triphosphatase.
This enzyme determines the speed of muscle contraction. One ATP molecule contains enough energy for
the myosin bridges to turn once when released. This rotation is known as a stroke and causes the muscle
to contract.
The bridges move in the following sequence:
- They uncouple from the actin filament.
- Return to original position.
- They adhere to a new area of actin.
- They make a stroke.
- Then another ATP molecule triggers the next stroke.All muscles make single strokes at the same speed. The faster adenosine triphosphatase is broken down
inside the muscle fiber, the greater the number of strokes that bridges can be completed per unit of time
and the faster the muscle contracts.
ATPase activity is an inherited parameter. It cannot be influenced by training.
- Oxidative, intermediate and glycolytic
The oxidative potential of a muscle is determined by the number of mitochondria within the fiber. A
mitochondrion is a cell organelle (that is, one of those parts of the cell that specializes in performing
certain functions). Mitochondria are responsible for the following chain of processes:
The breakdown of fat or glucose into water and carbon dioxide.
ATP resynthesis.
Resynthesis of creatine phosphate using ATP.
Resynthesis of myofibrillar ATP molecules using creatine phosphate.
Muscle contraction.
Glucose can be broken down in muscle tissue, including outside the mitochondria. Then pyruvate is
produced from it, and ATP resynthesis also starts. A person will feel fatigue in the muscle as lactic acid is
formed there.
According to this criterion, muscle fibers are classified into three types:
Oxidative
– The mitochondrial mass is large initially. No matter how long a person trains and no matter how much
he increases the load, this mass will not increase significantly.
Intermediate
Compared to the previous type of fiber, the mitochondrial mass is significantly less. As the muscle works,
lactic acid accumulates in it. Fatigue does not develop quickly compared to glycolytic fibers.
Glycolytic
The content of mitochondria is minimal. Fibers are characterized by anaerobic glycolysis, leading to
accelerated accumulation of lactic acid and rapid onset of fatigue.
During aerobic glycolysis, glucose inside mitochondria is broken down into ATP, water and carbon dioxide
with the participation of oxygen. In the anaerobic version of the process, oxygen is not involved, and
glucose is broken down into ATP and lactic acid.If a person does not exercise regularly, his oxidative muscle fibers are of the slow type, and the other two
types are of the fast type. If desired, the body’s endurance can be increased.
To do this, you need to choose workouts during which some of the glycolytic and intermediate fibers will
turn into oxidative ones, which means you will be less tired.
- Low-threshold and high-threshold
We are talking about the threshold of excitability of motor units. Each such unit consists of:
motor neuron;
axon;
collection of muscle fibers.
The number of motor units in the body does not change over time. Muscle contraction occurs under the
influence of nerve impulses of electrical nature emanating from the brain.
This occurs when the magnitude of the impulse is at or above the threshold value for a given motor unit.
When the impulse is below the threshold value, the motor unit remains