A key factor in developing a defined physique is increasing muscle size. To achieve this, strength training and weightlifting are essential parts of a fitness program. The reason is that these types of exercise activate biological processes involved in building new muscle fibers and, consequently, increasing muscle size.
Find out what these processes are and what role white and red blood cells play in them in the following paragraphs.
What Are Muscle Growth, Hyperplasia, and Hypertrophy?
Muscles are made up of many individual fibers. When their number or volume increases, what is known as muscle growth occurs. The process of increasing the number of muscle fibers is called hyperplasia, while an increase in their volume is called hypertrophy.
Hyperplasia
There is little data on the exact effect of strength training on increasing the number of muscle fibers. However, a study conducted on rodents found that it does have an effect, with the greatest increase observed after exposure to a heavy load.
New fibers are often smaller, and some researchers believe this is because existing fibers split into smaller ones, increasing their number.
Researchers have also observed signs of fiber splitting in humans after high-intensity strength training, but there is still no conclusive evidence that long-term strength training causes a continuous increase in the number of muscle fibers.
Hypertrophy
Hypertrophy is the process of increasing the volume of individual muscle fibers. This can happen in two ways: by increasing their diameter or their length.
The idea that muscle fibers grow longer may sound strange, since each muscle in our body has a fixed location, beginning, and end that cannot be changed. However, a muscle can appear longer after training as it bulges in the middle.
Many studies show that muscle fascicle length (fascicles are groups of muscle fibers) increases after prolonged strength training. This most often happens when a training program focuses primarily on eccentric contractions—they occur when muscles lengthen. Lengthening during eccentric contractions places a high level of stress on the working muscles, making injury much more likely than with concentric contractions.
Which Mechanisms Stimulate Muscle Growth?
There are three mechanisms that lead to muscle growth: metabolic stress, mechanical tension, and muscle damage.
Metabolic stress
Metabolic stress is not one of the main drivers of muscle growth, but it still plays a role. It is a physiological process in which by-products such as lactate, inorganic phosphate, hydrogen ions, and others are released. In short, it involves the buildup of by-products in cells.
However, it supports muscle growth by increasing muscle fiber activation and stimulating the secretion of various hormones.
Mechanical tension
Mechanical tension is the tension created during the concentric phase of a movement (the shortening phase), which muscles experience as they contract. Muscle fibers can detect this tension through receptors in the cell membrane. When these receptors sense a mechanical load, the muscle fibers send signals to so-called satellite cells. These are dormant muscle precursor cells that activate only when the muscle needs help.
With the help of mechanical tension, satellite cells bind to the affected muscle fibers and begin producing new proteins to repair them. This starts the process of building new muscle tissue, known as protein synthesis.
Muscle damage
Any tearing or disruption to the integrity of muscle cells causes so-called muscle damage. This results from mechanical tension and triggers the activation of satellite cells.
When muscle fibers are damaged, they release substances that attract immune cells, whose role is to repair them. During the repair process, however, several proteins and anabolic hormones are released, activating satellite cells. In this way, muscle damage helps build new muscle tissue.
Until recently, muscle damage was often used as a primary mechanism for gaining muscle mass. In recent years, however, its benefits have been disproven, and it is even thought that it can do more harm than good, since the body must first repair the damage before starting to build new muscle tissue. Muscle damage cannot be avoided completely during training, but it is not advisable to deliberately increase it.
What are aerobic and anaerobic training, and how do they affect muscle growth?
Exercise is physical activity that requires a high energy expenditure. How this energy is supplied determines whether a workout is aerobic or anaerobic—that is, whether energy is produced in the presence or absence of oxygen.
Aerobic training
During aerobic training, the intensity is not too high, allowing the body to take in more oxygen. This oxygen is needed to break down fats and carbohydrates, releasing the energy required.
Fat requires more oxygen to burn, so workouts focused primarily on aerobic exercise are better suited to this purpose. They also improve heart health and fitness, as well as the body's ability to recover after intense exercise. This is due to the processes that take place in the body during these exercises, namely:
Improved endurance
Aerobic exercise relies mainly on slow-twitch muscle fibers. They contract slowly and at low intensity, and are important for improving endurance.
More and larger blood vessels
The increased flow of oxygen through the body and to the muscles during aerobic training leads to the formation of new small blood vessels, which carry this oxygen along with the blood. The blood vessels also increase in size.
These changes make it easier to transport not only oxygen but also nutrients to the muscles, and to remove waste products. All of this supports recovery and muscle growth.
More mitochondria and myoglobin (muscle hemoglobin)
Aerobic training speeds up important metabolic processes in muscle tissue, including an increase in mitochondria and the protein myoglobin. Mitochondria—the cell's energy factories—are needed to produce ATP (adenosine triphosphate) for energy. Myoglobin, in turn, delivers the oxygen required for this process. These changes improve the muscles' aerobic capacity.
Burning fat for energy
Increased blood flow to the muscles, more oxygen, a greater number of mitochondria, and a rise in the levels of enzymes used to convert fat—all these changes make it easier to burn fat to supply the muscles with energy. This leads to fat loss throughout the body.
Anaerobic training
Unlike aerobic training, anaerobic training produces energy without oxygen. This means the intensity is much higher, and oxygen cannot travel from the lungs to the cells quickly enough. In these cases, energy is released by breaking down carbohydrates alone, because fats cannot be oxidized.
However, anaerobic training also brings about important changes in the body that improve overall health and fitness.
More fast-twitch muscle fibers
Unlike aerobic training, which produces more slow-twitch muscle fibers for endurance, anaerobic training increases the size and number of fast-twitch muscle fibers. They contract quickly and therefore fatigue quickly, but they are thicker and help improve muscle strength and increase hypertrophy—their size.
Increased glycolysis, ATP, and creatine phosphate
Some of the metabolic changes driven by anaerobic training include increased glucose breakdown, a process known as glycolysis. This type of exercise also raises levels of ATP (adenosine triphosphate), the main source of energy in muscles, as well as creatine phosphate, which can quickly be converted into ATP.
What role do red and white blood cells play in building muscle mass?
Two of the main components of human blood are red and white blood cells. They have very different functions in the body and are essential for many processes.
The main function of red blood cells and their role in building muscle mass
Red blood cells support the most important function of the blood. They travel through the bloodstream to transport oxygen from the lungs to the rest of the body and carry carbon dioxide back to the lungs. These gases are transported by a protein in red blood cells known as hemoglobin. Hemoglobin makes up 95% of the volume of a red blood cell, and when it binds with oxygen, it gives these cells their characteristic red color.
During exercise, the cardiovascular system must ensure that substrates are delivered to working muscles. As mentioned above, the primary function of red blood cells is to transport oxygen from the lungs to the body's other tissues. They also release ATP (adenosine triphosphate), which helps dilate blood vessels and improve blood flow to working muscles. Athletes often have a low ratio of red blood cell volume to total blood volume, a condition commonly called “sports anemia.” However, this is not anemia in the true sense of the word, as athletes actually have more red blood cells and hemoglobin in their bloodstream than people who do not train.
The main function of white blood cells and their role in building muscle mass
White blood cells fight harmful bacteria, viruses, and fungi in the human body. They produce antibodies and are an important part of the immune system. They also help remove dead red blood cells from the body.
Every time you exercise, microscopic tears form in the muscle fibers and connective tissue. This releases chemical irritants that cause mild inflammation. As with any other inflammation, white blood cells become active and repair the damaged muscles.
Each time torn muscle fibers and connective tissue are repaired, they become stronger, larger, and more resilient. Regular workouts therefore lead to muscle growth and stronger tendons.