The outer covering of muscle cells is called the sarcolemma , and the inner gel of the cell is called the sarcoplasm. Within the sarcoplasm, myoglobin molecules store oxygen, and glycogen molecules store glucose. Oxygen and glucose provide energy for the muscle cell. Also within the sarcoplasm, actin and myosin filaments form protein chains that can glide and slide past one another during muscle contractions. Hypertrophy is an increase in the size of muscle cells.
When muscle tissue is placed under mechanical stress, myogenic stem cell activation occurs , which leads to repair of damaged muscle tissue and an increase in muscle cell size. Those mechanisms include:. So how do you safely put muscle tissue under stress to start the chain of events that lead to muscle hypertrophy?
Exercise and movement. The single most effective way to induce muscle hypertrophy is through exercise. High-intensity strength training exercises cause minor injury to skeletal muscle cells, and this sets in motion the release of anabolic hormones that create muscle hypertrophy. Think of strength training as creating slight stress and injury to your muscles.
Your body's repair of those muscles adapts to create tissue that is slightly stronger, preparing your muscles to effectively manage future stresses that could be placed upon them. Performing aerobic exercise has a similar effect on cardiac muscle tissue. Stressing your heart muscle within reason helps your cardiac tissue grow in response to this stress.
Regular aerobic exercise improves the efficiency of your heart muscle. You might not be able to perform high-intensity strength training at times, such as after an injury. But you may still want to create an environment where muscle growth and hypertrophy can occur. Sometimes, this is accomplished through blood flow restriction training.
This method of exercise therapy involves using specialized cuffs to restrict blood flow to muscles. Low intensity and high repetition exercises are performed, and the cuffs are then removed. Are the principles behind the term just some sketchy bro science, a passing fitness fad, or real, lab tested-and-proven physiology?
Rest assured, the hype is real. Hypertrophy is, by definition, the enlargement of an organ or tissue from the increase in size of its cells. Not to be confused with hyperplasia, the process of increasing the number of cells, hypertrophy is the process of increasing the size of the cells that are already there.
This occurs through a physiologic process that leads to an increased number of contractile proteins actin and myosin in each muscle fiber. With the right training regimen, you can catalyze this process — but helps to understand the science behind it. The body has the amazing potential to adapt to its environment. This includes building more strength when repeated stress to the tissue indicates a need to accommodate the new, higher loads.
Diet is another important consideration. People who want to build muscle should aim to eat a healthful diet rich in macronutrients. Protein is an important part of the diet for building muscle.
That said, the exact amount of protein necessary for muscle growth is still unclear. Research suggests that getting more than 1. Myostatin-related muscular hypertrophy is a rare condition that causes high muscle mass.
People with this condition have up to twice as much muscle mass. They typically also have low body fat. A genetic defect in the MSTN gene causes this condition. It disrupts the production of myostatin, which usually controls muscle growth. By reducing myostatin, the condition causes uncontrolled muscle growth. Muscular hypertrophy involves increasing muscle size, typically through strength training. Putting strain on the muscles through working out causes the body to repair them, resulting in an increase in muscle fibers.
Having more muscle fibers will lead to greater strength and muscle size. Strength training can involve a variety of exercises against some form of resistance. Increasing the resistance over time will lead to muscle hypertrophy.
Muscular hypertrophy can take time to produce noticeable changes in muscle size or strength. In addition to strength training, people should also incorporate healthful habits — such as eating a balanced diet and getting plenty of sleep — to optimize muscle gain and strength.
A look at how long it takes to build muscle by working out. Included is detail on macronutrients and the best way to build muscle safely and…. Performing particular exercises and eating the right foods can help a person build muscle over time. Learn about the types of exercise and diet that…. The human muscular system is complex and has many functions in the body. Progressive overload is a means of applying varying and intermittent levels of stress to skeletal muscle, making it adapt by generating comparable amounts of tension.
The muscle is able to adapt by increasing the size and amount of contractile proteins, which comprise the myofibrils within each muscle fiber, leading to an increase in the size of the individual muscle fibers and their consequent force production 1.
The Physiology of Skeletal Muscle Hypertrophy The physiology of skeletal muscle hypertrophy will explore the role and interaction of satellite cells, immune system reactions, and growth factor proteins See Figure 1.
Satellite Cells Satellite cells function to facilitate growth, maintenance and repair of damaged skeletal not cardiac muscle tissue 2. These cells are termed satellite cells because they are located on the outer surface of the muscle fiber, in between the sarcolemma and basal lamina uppermost layer of the basement membrane of the muscle fiber.
Satellite cells have one nucleus, with constitutes most of the cell volume. Usually these cells are dormant, but they become activated when the muscle fiber receives any form of trauma, damage or injury, such as from resistance training overload. The satellite cells then proliferate or multiply, and the daughter cells are drawn to the damaged muscle site.
They then fuse to the existing muscle fiber, donating their nuclei to the fiber, which helps to regenerate the muscle fiber. It is important to emphasize the point that this process is not creating more skeletal muscle fibers in humans , but increasing the size and number of contractile proteins actin and myosin within the muscle fiber see Table 1. This satellite cell activation and proliferation period lasts up to 48 hours after the trauma or shock from the resistance training session stimulus 2.
The amount of satellite cells present within in a muscle depends on the type of muscle. Type I or slow-twitch oxidative fibers, tend to have a five to six times greater satellite cell content than Type II fast-twitch fibers , due to an increased blood and capillary supply 2.
This may be due to the fact that Type 1 muscle fibers are used with greatest frequency, and thus, more satellite cells may be required for ongoing minor injuries to muscle. Immunology As described earlier, resistance exercise causes trauma to skeletal muscle. The immune system responds with a complex sequence of immune reactions leading to inflammation 3. The purpose of the inflammation response is to contain the damage, repair the damage, and clean up the injured area of waste products.
The immune system causes a sequence of events in response to the injury of the skeletal muscle. Macrophages, which are involved in phagocytosis a process by which certain cells engulf and destroy microorganisms and cellular debris of the damaged cells, move to the injury site and secrete cytokines, growth factors and other substances.
Cytokines are proteins which serve as the directors of the immune system. They are responsible for cell-to-cell communication. Cytokines stimulate the arrival of lymphocytes, neutrophils, monocytes, and other healer cells to the injury site to repair the injured tissue 4. They are responsible for protein breakdown, removal of damaged muscle cells, and an increased production of prostaglandins hormone-like substances that help to control the inflammation.
Growth Factors Growth factors are highly specific proteins, which include hormones and cytokines, that are very involved in muscle hypertrophy 6. Growth factors stimulate the division and differentiation acquisition of one or more characteristics different from the original cell of a particular type of cell. In regard with skeletal muscle hypertrophy, growth factors of particular interest include insulin-like growth factor IGF , fibroblast growth factor FGF , and hepatocyte growth factor HGF.
These growth factors work in conjunction with each other to cause skeletal muscle hypertrophy. It regulates insulin metabolism and stimulates protein synthesis. In response to progressive overload resistance exercise, IGF-I levels are substantially elevated, resulting in skeletal muscle hypertrophy 7.
FGF has nine forms, five of which cause proliferation and differentiation of satellite cells, leading to skeletal muscle hypertrophy. The amount of FGF released by the skeletal muscle is proportional to the degree of muscle trauma or injury 8.
Specific to skeletal muscle hypertrophy, HGF activates satellite cells and may be responsible for causing satellite cells to migrate to the injured area 2. Hormones in Skeletal Muscle Hypertrophy Hormones are chemicals which organs secrete to initiate or regulate the activity of an organ or group of cells in another part of the body. It should be noted that hormone function is decidedly affected by nutritional status, foodstuff intake and lifestyle factors such as stress, sleep, and general health.
The following hormones are of special interest in skeletal muscle hypertrophy.
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