근육 증가(근형질 비대, 근원섬유 비대)의 과학! 근력강화, 근비대의 과학

[문형철]

근력과 근지구력이 증가한다는 것은 근섬유 관점에서 어떤 의미인가?

보디빌더가 힘이 센것은 아니다. 

근지구력운동은 slow twitch(type 1 muscle fiber) 트레이닝

근력운동은 fast twitch(type 2 muscle fiber) 트레이닝

근형질 비대와 근원섬유 비대

panic bird....

근력, 근지구력을 기르기 위한 운동법

1) 근지구력을 위한 운동은 1RM의 60% 정도의 근력으로 20회이상 반복

2) 근비대를 위한 운동은 1RM의 70% 정도의 근력으로 8~20회 반복

3) 근력을 위한 운동은 1RM의 80% 정도의 근력으로 2~6회 반복

4) 최대 힘을 기르기 위한 운동은 1RM의 90%의 힘으로 2~3회 반복

찾고자 하는 의문

근력 증가를 위한 운동을 통해서 근육, 근속, 근섬유, 근원섬유, 근막, motor unit의 시냅스는 어떻게 달라지는가? 

근지구력 증가를 위한 운동?

최대 힘 증가를 위한 운동? 

그 과정에서 근육량이 늘어난다는 것은 어떤 의미일까? 

근비대란?

Muscle hypertrophy involves an increase in size of skeletal muscle through an increase in the size of its component cells. Hypertrophy can be broken down into two types of categories:myofibrillar and sarcoplasmic. Each of these specific types of muscle hypertrophy will result in increasing size of cells, but not of equal effect. 

1) Sarcoplasmic hypertrophy is focused on increasing the actual size of the muscle, and less on increasing strength. 

근형질 비대

2) Myofibril hypertrophy will focus more on strength increase and less on an increase in the size of the skeletal muscle.

Strength training[edit]

Main article: Strength training

Strength training typically produces a combination of the two different types of hypertrophy: contraction against 80 to 90% of the one-repetition maximum for 2–6 repetitions (reps) causes myofibrillated hypertrophy to dominate (as in powerlifters, Olympic lifters and strength athletes), whereas several repetitions (generally 8–12 for bodybuilding or 12 or more for muscular endurance) against a submaximal load facilitates mainly sarcoplasmic hypertrophy (professional bodybuilders and endurance athletes).^{[citation needed]} 

- 근원섬유 비대, 올림픽 역도선수 근력, 1RM의 80~90% 힘, 2~6 반복운동

- 근형질 비대, 바디빌더 근육비대, 1RM의 70% 8~12회, 60%힘으로 12회 이상 반복운동

The first measurable effect is an increase in the neural drive stimulating muscle contraction. Within just a few days, an untrained individual can achieve measurable strength gains resulting from "learning" to use the muscle.^{[citation needed]} 

신경추동자극 근수축 증가를 측정할 수 있음.

한번도 근력운동을 하지 않은 개인은 며칠내에 측정가능한 근력 증가를 얻을 수 있는데, 이는 근육 사용의 방법을 배워서 증가한 것임. 

As the muscle continues to receive increased demands, the synthetic machinery is upregulated. Although all the steps are not yet clear, this upregulation appears to begin with the ubiquitous second messenger system (including phospholipases, protein kinase C, tyrosine kinase, and others).^{[citation needed]} These, in turn, activate the family of immediate-early genes, including c-fos, c-jun and myc. These genes appear to dictate the contractile protein gene response.^{[citation needed]}

근육이 지속적으로 증가하는 요구를 받을때, 근육합성 시스템은 상향조절됨. 이 과정은 분명하게 밝혀져 있지는 않지만, 인지질 가수분해요효(Phospholipase), 

단백질 효소(protein kinase), 티로신 효소 등의 2차 전달계와 함께 상향조절됨. c-fos, c-jun and myc와 같은 유전자를 활성화 함. 이러한 유전자는 수축구조 단백질 유전자 반응을 지시하기 시작함. 

Progressive overload is considered the most important principle behind hypertrophy, so increasing the weight, repetitions (reps), and sets will all have a positive impact on growth. Some experts create complicated plans that manipulate weight, reps, and sets, increasing one while decreasing the others to keep the schedule varied and less repetitive.

점차적으로 부하를 증가시키는 것은  중요한 근비대의 원리로 인정됨. 그래서 무게를 높이는 것과 반복횟수, 세트수를 높이는 것은 근육 성장에 긍정적인 역할을 함. 

Anaerobic training[edit]

Main article: Anaerobic exercise

Experts and professionals differ widely on the best approaches to specifically achieve muscle growth (as opposed to focusing on gaining strength, power, or endurance); it was generally considered that consistent anaerobic strength training will produce hypertrophy over the long term, in addition to its effects on muscular strength and endurance. 

지속적인 무산소적 근력 트레이닝은 오랜 기간을 거쳐 근비대를 만들어냄. 또한 근력과 근지구력에도 영향을 줌. 

Muscular hypertrophy can be increased through strength training and other short-duration, high-intensity anaerobic exercises. Lower-intensity, longer-duration aerobic exercise generally does not result in very effective tissue hypertrophy; instead, endurance athletes enhance storage of fats and carbohydrates within the muscles,^[1] as well as neovascularization.^[2][3]

근비대는 근력 트레이닝와 짧은 기간, 높은 강도의 무산소적 운동을 통해 증가될 수 있음. 

저강도, 오랜기간, 유산소적 운동은 일반적으로 효과적인 조직비대를 일으키지 못함. 대신에 지구력 운동선수는 근육내에 지방과 탄수화물의 저장능력 그리고 신생혈관을 증진시킴. 

Several biological factors such as age and nutrition can affect muscle hypertrophy. During puberty in males, hypertrophy occurs at an increased rate. Natural hypertrophy normally stops at full growth in the late teens. An adequate supply of amino acids is essential to produce muscle hypertrophy. As testosterone is one of the body's major growth hormones, on average, men find hypertrophy much easier to achieve than women. Taking additional testosterone, as in anabolic steroids, will increase results. It is also considered a performance-enhancing drug, the use of which can cause competitors to be suspended or banned from competitions. In addition, testosterone is also a medically regulated substance in most countries, making it illegal to possess without a medical prescription.

몇가지 생리학적 요소인 나이, 영양은 근비대에 영향을 미침. 남성 사춘기에 근비대는 높은 비율로 일어남. 일반적인 근비대는 십대후반에 최대성장을 멈춤. 적절한 아미노산 공급은 근비대에 필수적 요소임. 

테스토스테론은 가장 중요한 성장인자로 여성보다 남성 근비대가 쉽게 일어나는 이유는 여기에 있음. 

Protein synthesis[edit]

Main article: Protein biosynthesis

Ultimately the message filters down to alter the pattern of protein expression‎. The additional contractile proteins appear to be incorporated into existing myofibrils (the chains of sarcomeres within a muscle cell). There appears to be some limit to how large a myofibril can become: at some point, they split. These events appear to occur within each muscle fiber. That is, hypertrophy results primarily from the growth of each muscle cell, rather than an increase in the number of cells. Skeletal muscle cells are however unique in the body in that they can contain multiple nuclei, and the number of nuclei can increase.^[4]

궁극적으로 단백질 발현 패턴의 변화임. 

Cortisol decreases amino acid uptake by muscle tissue, and inhibits protein synthesis.^[5] The short-term increase in protein synthesis that occurs subsequent to resistance training returns to normal after approximately 28 hours in adequately fed male youths. ^[6] 

코티솔은 근육조직에서 아미노산을 감소시켜, 단백질 합성을 방해함. 

짧은 시간동안에는 단백질합성을 증가시킴. 

Another study determined that muscle protein synthesis was elevated even 72 hours following training.^[7] A small study performed on young and elderly found that ingestion of 340 grams of lean beef (90 g protein) did not increase muscle protein synthesis any more than ingestion of 113 grams of lean beef (30 g protein). In both groups, muscle protein synthesis increased by 50%. The study concluded that more than 30 g protein in a single meal did not further enhance the stimulation of muscle protein synthesis in young and elderly.^[8] However, this study didn't check protein synthesis in relation to training; therefore conclusions from this research are controversial.

트레이닝 후 72시간이 지나면 단백질 합성이 증가함. 

소고기 340 그램, 113그램은 단백질합성의 차이가 없이 단백질 합성이 50% 증가함. 

결론적으로 30 g protein이상 음식을 먹어도 단백질 합성을 증가시키지는 않음. 하지만 이 연구는 트레이닝과 연관되어 단백질합성을 체크하지는 않음. 그래서 결론은 논란이 많음...

It is not uncommon for bodybuilders to advise a protein intake as high as 2–4 g per kilogram of bodyweight per day.^[9] However, scientific literature has suggested this is higher than necessary, as protein intakes greater than 1.8 g per kilogram of body weight showed to have no greater effect on muscle hypertrophy.^[10] 

바디빌더에게 하루에 체중 1킬로그램당 2~4g의 단백질을 섭취하라고 요구하는 것은 흔한 조언임. 

하지만 과학적 연구에 따르면 실제 요구량보다 많음. 근비대에 영향을 주는 양은 1킬로그램당 1.8g이면 충분함. 

계산 : 10킬로는 18g, 50킬로는 90g, 100킬로는 180g

A study carried out by American College of Sports Medicine (2002) put the recommended daily protein intake for athletes at 1.2–1.8 g per kilogram of body weight.^[11][12][10] Conversely, Di Pasquale (2008), citing recent studies, recommends a minimum protein intake of 2.2 g/kg "for anyone involved in competitive or intense recreational sports who wants to maximize lean body mass but does not wish to gain weight. However athletes involved in strength events (..) may need even more to maximize body composition and athletic performance. In those attempting to minimize body fat and thus maximize body composition, for example in sports with weight classes and in bodybuilding, it’s possible that protein may well make up over 50% of their daily caloric intake."^[13]

논란...

Microtrauma[edit]

Main article: Microtrauma

Microtrauma, which is tiny damage to the fibers, may play a significant role in muscle growth. ^[14] When microtrauma occurs (from weight training or other strenuous activities), the body responds by overcompensating, replacing the damaged tissue and adding more, so that the risk of repeat damage is reduced. Damage to these fibers have been theorized as the possible cause for the symptoms of delayed onset muscle soreness (DOMS), and is why progressive overload is essential to continued improvement, as the body adapts and becomes more resistant to stress.

미세손상은 근섬유에 작은 손상을 주는 것으로 근비대에 중요한 역할을 함. 

강력한 근력운동을 통해 근육에 미세손상이 발생하면 인체는 과보상 반응에 의해서 근비대가 일어남. 

근섬유의 미세손상에 의해서 DOMS가 발생함. 그래서 점진적인 과부하는 지속적인 근비대를 위해서 필수적임. 

In the bodybuilding and fitness community and even in some academic books skeletal muscle hypertrophy is described as being in one of two types: Sarcoplasmic or myofibrillar. According to this hypothesis, during sarcoplasmic hypertrophy, the volume of sarcoplasmic fluid in the muscle cell increases with no accompanying increase in muscular strength, whereas during myofibrillar hypertrophy, actin and myosin contractile proteins increase in number and add to muscular strength as well as a small increase in the size of the muscle. 

근섬유 비대는 근형질 비대와 근원섬유 비대 두가지로 나뉨.

이 가설에 따르면 근형질 비대는 근섬유내에 Sarcoplasmic fluid가 증가하는 것으로 근력은 증가는 수반하지 않음. 

반면에 근원섬유 비대는 액틴과 마이오신 양이 증가하여 근력이 증가할 뿐 아니라 근육의 사이즈도 증가함. 

Sarcoplasmic hypertrophy is greater in the muscles of bodybuilders while myofibrillar hypertrophy is more dominant in Olympic weightlifters.^[15] These two forms of adaptations rarely occur completely independently of one another; one can experience a large increase in fluid with a slight increase in proteins, a large increase in proteins with a small increase in fluid, or a relatively balanced combination of the two.

근형질 비대는 바디빌더에서 발생하고, 근원섬유비대는 올림픽 역도선수에게서 우세하게 발생함. 

Examples of increased muscle hypertrophy are seen in various professional sports, mainly strength related sports such as boxing, bodybuilding, mixed martial arts, rugby, professional wrestling and various forms of gymnastics. These athletes train extensively in strength as well as cardiovascular and muscular endurance training.

The Mystery of Skeletal Muscle Hypertrophy Richard Joshua Hernandez, B.S. and Len Kravitz, Ph.D.  Introduction Through exercise, the muscular work done against a progressively challenging overload leads to increases in muscle mass and cross-sectional area, referred to as hypertrophy. But why does a muscle cell grow and how does it grow? Although an intense topic of research, scientists still do not fully understand the complete (and very complex) picture of how muscle adapts to gradually overloading stimuli. In this article, a brief but relevant review of the literature is presented to better understand the multifaceted phenomenon of skeletal muscle hypertrophy. 운동을 통해서 과부하를 점차적으로 증가시키는 근육일(muscular work)은 근질량(Muscle mass)과 근단면적(muscle cross-sectional area)을 증가시켜 "근비대"를 초래함. 하지만 근육세포가 왜 커지고 어떻게 커지는가?  많은 연구에도 불구하고 과학자들은 아직까지 근육이 점차적으로 증가하는 과부하자극에 어떻게 적응하는지 완전한 이해에 도달하지 못함. 이 논문에서 골격근 비대의 다양한 방면의 현상을 이해할것임. What is Muscular Hypertrophy? Muscular hypertrophy is an increase in muscle mass and cross-sectional area (1). The increase in dimension is due to an increase in the size (not length) of individual muscle fibers. Both cardiac (heart) and skeletal muscle adapt to regular, increasing work loads that exceed the preexisting capacity of the muscle fiber. With cardiac muscle, the heart becomes more effective at squeezing blood out of its chambers, whereas skeletal muscle becomes more efficient at transmitting forces through tendonous attachments to bones (1). 근비대는 근질량과 단면적이 증가하는 것임. 이러한 수치의 증가는 개별 근섬유의 크기(길이가 아님)가 증가하기 때문임.  심장근육은 심방, 심실안의 혈액을 좀더 잘 짜 보내는 역할을 함 골격근은 관절을 움직이는 힘의 전달을 좀더 효과적으로 하게 함.  최대 힘분출은 "1000%까지 증가" 근력, 근지구력 운동을 시행하면 위 그림과 같이 근비대는 1~2주 이후부터 나타나는데도 불구하고 바로 힘이 증가함. 그 이유는 neural firing frequency, neural synchronization, Presynaptic inhibition, MVIC,  변화로 힘이 증가함.  neural firing frequency(반응속도의 증가)는 40%을 증가시킴.  Skeletal muscle has two basic functions: to contract to cause body movement and to provide stability for body posture. Each skeletal muscle must be able to contract with different levels of tension to perform these functions. 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). 골격근은 두가지 기능 1) 신체움직임을 유발하기 위한 근수축 2) 신체자세를 위한 안정성 제공 각각의 골격근은 이러한 기능을 수행하기 위한 다양한 장력으로 수축해야 함.  증가되는 부하는 골격근에 가해지는 다양한 장력부하가 주어진다는 의미이고, 그것은 비교가능한 양의 장력에 의해서 적응함.  근육은 크기증가와 수축 단백질의 양 증가에 의해서 적응할 수 있음. 그것은 각각 근섬유내 근원섬유를 포함한 개념으로 각각 근섬유 크기 증가를 유도하고 힘생성을 야기함.  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. for Summary). 골격근 비대의 생리학은 위성세포, 면역시스템 반응, 성장인자 단백질의 상호작용과 역할을 탐구할 수 있음.  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. 위성세포는 골격근 조직의 회복과 유지, 성장을 촉진하는역할을 함. 위성세포는 근섬유의 바깥 표면 근초와 basal lamina 사이에 위치하기때문에 이름 붙여짐. 위성세포는 하나의 세포핵을 가지고, 근육세포 용적의 일부를 구성함.  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.  대개 이 세포들은 평소에 휴면기이지만 근섬유가 타박상, 손상을 받을때 활성화됨.  근육세포가 손상되면 위성세포는 증식하고, 딸세포(daughter cell)는 손상된 근육부위로 이동함. 그리고 근섬유를 연결하고 근섬유에 핵을 만들고 근섬유 재생을 도움.  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. for a summary of changes that occur to muscle fibers as they hypertrophy). This satellite cell activation and proliferation period lasts up to 48 hours after the trauma or shock from the resistance training session stimulus (2).  이 과정은 인체 골격근 섬유를 더 만드는 것이 아니고, 근섬유내 근육 수축 단백질인 액틴과 마이오신의 숫자와 크기를 증가시키는 것임.  위성세포 활성과 증식기간은 근육손상 후 48시간까지 지속되거나 저항 트레이닝 기간동안 계속 지속됨.  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. 위성세포의 양은 근섬유 타입에 의존함. 느린연축산소섬유 type1은 풍부한 혈관, 미세혈관을 가지고 있기 때문에 빠른연축 type2섬유보다 5~6배 많은 위성세포를 가지고 있음.  type1 근섬유는 좀더 많은 위성세포가 있어서 계속 진행중인 근육의 미세손상에 필요할 수 있음.  참고) 근육노화과정에서 type 2 빠른 연축섬유의 위성세포의 기능이 더 빨리 감소함.  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). 저항운동은 골격근에 손상을 야기함. 면역시스템은 면역반응의 복잡한 과정을 통해 염증반응을 일으킴. 이 염증반응의 목적은 손상을 흡수하고 조직손상을 회복하고, 손상조직의 찌거기 부산물을 제거하기 위함.  면역시스템은 골격근 손상에 반응하여 일련의 반응을 일으킴. 대식세포는 손상부위로 이동하여 사이토카인, 성장인, 다른 물질 등을 분비하고 손상되 세포를 탐식함. 사이토카인은 단백질로 면역반응의 직접조절자임. 사이토카인은 세포와 세포 소통을 담당함. 사이토카인은 임파구, 중성구, 단핵구 등을 자극하여 손상조직을 수복함.  The three important cytokines relevant to exercise are Interleukin-1 (IL-1), Interleukin-6 (IL-6), and tumor necrosis factor (TNF). These cytokines produce most of the inflammatory response, which is the reason they are called the “inflammatory or proinflammatory cytokines” (5). 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). 세가지 중요한 사이토카인이 있음. 인터루킨 1, 인터루킨 6, 종양괴사인자 이러한 사이토카인은 염증반응 물질을 생성하기 때문에 염증성 사이토카인이라고 부름. 그것들은 단백질 파괴, 손상세포의 제거, 프로스타글란딘 생성증가를 담당함.  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. 성장인자는 높은 특이성을 가진 단백질로 호르몬과 사이토카인을 포함함.  성장인자는 근비대와 연관성이 있음.  성장인자는 특별한 형태의 세포를 분화, 갈라짐을 자극함.  골격근의 비대와 성장인자인 IGF, FGF, HGF를 포함함. 이러한 성장인자는 다른 물질과 함께 작용하여 골격근 비대를 야기함.  Insulin-Like Growth Factor IGF is a hormone that is secreted by skeletal muscle. It regulates insulin metabolism and stimulates protein synthesis. There are two forms, IGF-I, which causes proliferation and differentiation of satellite cells, and IGF-II, which is responsible for proliferation of satellite cells. In response to progressive overload resistance exercise, IGF-I levels are substantially elevated, resulting in skeletal muscle hypertrophy (7). IGF는 근육에서 분비하는 호르몬임. 이것은 인슐린 대사를 조절하고 단백질 합성을 자극함. IGF1, 2두가지 형태가 있음. 이것은 위성세포의 증식과 분화를 야기함.  점차적인 과부하 운동에 반응하여 IGF 1레벨은 증가하고 근비대를 일으킴.  Fibroblast Growth Factor FGF is stored in skeletal muscle. 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). FGF는 골격근에 저장되어 있음. FGF는 9개 형태가 있고, 그중 5개는 위성세포의 증식과 분화를 야기하고, 골격근 비대를 유발함. 골격근에서 분비된 IGF양은 근육 손상의 정도와 비례하여 증가함.  Hepatocyte Growth Factor HGF is a cytokine with various different cellular functions. Specific to skeletal muscle hypertrophy, HGF activates satellite cells and may be responsible for causing satellite cells to migrate to the injured area (2).   HGF는 다양한 세포기능을 일으키는 사이토카인임. 특이하게 근비대와 연관됨. HGF는 위성세포를 자극하여 위성세포가 손상부위로 이동하는 것을 담당할 것임.  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. Growth Hormone Growth hormone (GH) is a peptide hormone that stimulates IGF in skeletal muscle, promoting satellite cell activation, proliferation and differentiation (9). However, the observed hypertrophic effects from the additional administration of GH, investigated in GH-treated groups doing resistance exercise, may be less credited with contractile protein increase and more attributable to fluid retention and accumulation of connective tissue (9). 성장호르몬은 골격근에서 IGF를 자극하는 펩타이드 호르몬으로 위성세포 활성화, 증식, 분화를 촉진함. 하지만 ... Cortisol Cortisol is a steroid hormone (hormones which have a steroid nucleus that can pass through a cell membrane without a receptor) which is produced in the adrenal cortex of the kidney. It is a stress hormone, which stimulates gluconeogenesis, which is the formation of glucose from sources other than glucose, such as amino acids and free fatty acids. Cortisol also inhibits the use of glucose by most body cells. This can initiate protein catabolism (break down), thus freeing amino acids to be used to make different proteins, which may be necessary and critical in times of stress. In terms of hypertrophy, an increase in cortisol is related to an increased rate of protein catabolism. Therefore, cortisol breaks down muscle proteins, inhibiting skeletal muscle hypertrophy (10).  코르티솔은 수용기 없이 세포벅을 통과하는 스테로이들 호르몬으로 신장의 부신에서 생성됨. 신생당합성을 촉진하고 포도당합성, 아미노산, 지방산 등과 같은 ... 코르티솔은 단백질 이화작용과 관련이 있어 근비대 생성을 억제함.  Testosterone Testosterone is an androgen, or a male sex hormone. The primary physiological role of androgens are to promote the growth and development of male organs and characteristics. Testosterone affects the nervous system, skeletal muscle, bone marrow, skin, hair and the sex organs.  With skeletal muscle, testosterone, which is produced in significantly greater amounts in males, has an anabolic (muscle building) effect. This contributes to the gender differences observed in body weight and composition between men and women. Testosterone increases protein synthesis, which induces hypertrophy (11). 테스토스테론은 성호르몬임. 주요 역할은 남성의 기관 특성 발달을 자극함.  테스토스테론은 신경계, 골격근, 골수, 피부, 생식기관에 영향을 미침. 골격근에서 테스토스테론은 남성에스 특히 증가하여 근육 만드는 역할에 참여함. .. Fiber Types and Skeletal Muscle Hypertrophy The force generated by a muscle is dependent on its size and the muscle fiber type composition. Skeletal muscle fibers are classified into two major categories; slow-twitch (Type 1) and fast-twitch fibers (Type II). The difference between the two fibers can be distinguished by metabolism, contractile velocity, neuromuscular differences, glycogen stores, capillary density of the muscle, and the actual response to hypertrophy (12). 힘은 근육의 크기와 근섬유 타입조성에 의해서 생성됨.  골격근 섬유는 느린연축섬유와 빠른 연축섬유로 분류함. 두 섬유의 차이는 대사, 수축속도, 신경섬유차이, 글리코겐저장, 미세혈관 밀집도 차이에 의해서 분류되고, 근비대에 반응함.  Type I Fibers Type I fibers, also known as slow twitch oxidative muscle fibers, are primaritly responsible for maintenance of body posture and skeletal support. The soleus is an example of a predominantly slow-twitch muscle fiber. An increase in capillary density is related to Type I fibers because they are more involved in endurance activities. These fibers are able to generate tension for longer periods of time. Type I fibers require less excitation to cause a contraction, but also generate less force. They utilize fats and carbohydrates better because of the increased reliance on oxidative metabolism (the body’s complex energy system that transforms energy from the breakdown of fuels with the assistance of oxygen) (12).  Type I fibers have been shown to hypertrophy considerably due to progressive overload (13,15). It is interesting to note that there is an increase in Type I fiber area not only with resistance exercise, but also to some degree with aerobic exercise (14). 느린 연축섬유 1섬유는 자세유지와 골격유지에 주요 역할을 담당함.  가자미근은 대표적인 느린연축섬유임. 혈관이 많고 주로 지구력 활동과 연관됨. 이 섬유는 오랜 시간의 장력을 만들어냄. 타입 1섬유는 수축속도가 느리고 적은 힘을 생성함.  흥미롭게도 느린연축섬유는 저항운동(근지구력운동)뿐 아니라 유산소운동에서도 근비대가 일어남.  Type II Fibers Type II fibers can be found in muscles which require greater amounts of force production for shorter periods of time, such as the gastrocnemius and vastus lateralis. Type II fibers can be further classified as Type IIa and Type IIb muscle fibers.  비복근, 외측광근과 같은 많은 힘을 생성하는 근육에서 많이 발견됨.  Type IIa Fibers Type IIa fibers, also known as fast twitch oxidative glycolytic fibers (FOG), are hybrids between Type I and IIb fibers. Type IIa fibers carry characteristics of both Type I and IIb fibers. They rely on both anaerobic (reactions which produce energy that do not require oxygen), and oxidative metabolism to support contraction (12). With resistance training as well as endurance training, Type IIb fibers convert into Type IIa fibers, causing an increase in the percentage of Type IIa fibers within a muscle (13). Type IIa fibers also have an increase in cross sectional area resulting in hypertrophy with resistance exercise (13). With disuse and atrophy, the Type IIa fibers convert back to Type IIb fibers.  이 섬유는 fast twitch oxidative glycolytic fibers로 타입 1과 2b의 중간 형태의 근섬유.  타입 2b 섬유는 저항운동(근지구력운동)을 시행하면 타입 2a섬유로 변경되어 근육내 타입 2a섬유의 비율이 증가함.  타입 2a 섬유는 또한 근육단면적 증가를 가지면서 저항운동과 함께 근비대를 야기함.  고정 등으로 근육을 사용하지 않아 근위축이 발생하면 타입 2a 섬유는 타입 2b섬유로 되돌아감.  아래 그림과 같이 13%정도가 변화함.  Type IIb Fibers Type IIb fibers are fast-twitch glycolytic fibers (FG). These fibers rely solely on anaerobic metabolism for energy for contraction, which is the reason they have high amounts of glycolytic enzymes. These fibers generate the greatest amount of force due to an increase in the size of the nerve body, axon and muscle fiber, a higher conduction velocity of alpha motor nerves, and a higher amount of excitement necessary to start an action potential (12). Although this fiber type is able to generate the greatest amount of force, it is also maintains tension for a shortesst period of time (of all the muscle fiber types).  type 2b 섬유는 빠른 연축 섬유임. 근수축을 위한 에너지를 만드는데, 무산소적 대사에 의존하고 이는 해당작용효소(glycolytic enzymes)를 많이 가져야 하는 이유임.  type 2b섬유는 가장 큰 힘을 내는데 "근섬유, 축삭, 신경체 크기 증가, 알파운동섬유의 높은 전도속도, 활동전위시작의 높은 양의 수축"이 증가해서임. 큰힘을 내지만 오래지속하지 못함.  Type IIb fibers convert into Type IIa fibers with resistance exercise. It is believed that resistance training causes an increase in the oxidative capacity of the strength-trained muscle. Because Type IIa fibers have a greater oxidative capacity than Type IIb fibers, the change is a positive adaptation to the demands of exercise (13). 저항운동을 하면 type 2b섬유는 type 2a섬유로 변화하여 type2a 섬유가 많아짐. 이는 근력트레이닝 근육의 산소사용능력이 증가하기 때문으로 믿어짐. 그래서 강한 힘을 내면서도 산소이용능력이 증가하기 때문에 오래 사용할 수 있음.  Conclusion Muscular hypertrophy is a multidimensional process, with numerous factors involved. It involves a complex interaction of satellite cells, the immune system, growth factors, and hormones with the individual muscle fibers of each muscle. Although our goals as fitness professionals and personal trainers motivates us to learn new and more effective ways of training the human body, the basic understanding of how a muscle fiber adapts to an acute and chronic training stimulus is an important educational foundation of our profession.  근섬유비대는 위성세포, 면역시스템, 성장인자, 호르몬 등의 복잡한 상호작용이 관여한 다면적 과정임.  Table 1. Structural Changes that Occur as a Result of Muscle Fiber Hypertrophy Increase in actin filaments Increase in myosin filaments Increase in myofibrils Increase in sarcoplasm Increase in muscle fiber connective tissue Source: Wilmore, J.H. and D. L. Costill. Physiology of Sport and Exercise (2nd Edition).Champaign, IL: Human Kinetics, 1999. 참고) 다른 인터넷 자료 References 1. Russell, B., D. Motlagh,, and W. W. Ashley. Form follows functions: how muscle shape is regulated by work. Journal of Applied Physiology 88: 1127-1132, 2000. 2. Hawke, T.J., and D. J. Garry. Myogenic satellite cells: physiology to molecular biology. Journal of Applied Physiology. 91: 534-551, 2001. 3. Shephard, R. J. and P.N. Shek. Immune responses to inflammation and trauma: a physical training model. Canadian Journal of Physiology and Pharmacology 76: 469-472, 1998. 4. Pedersen, B. K. Exercise Immunology. New York: Chapman and Hall; Austin: R. G. Landes, 1997.  5. Pedersen, B. K. and L Hoffman-Goetz. Exercise and the immune system: Regulation, Integration, and Adaptation. Physiology Review 80: 1055-1081, 2000. 6. Adams, G.R., and F. Haddad. The relationships among IGF-1, DNA content, and protein accumulation during skeletal muscle hypertrophy. Journal of Applied Physiology 81(6): 2509-2516, 1996. 7. Fiatarone Singh, M. A., W. Ding, T. J. Manfredi, et al. Insulin-like growth factor I in skeletal muscle after weight-lifting exercise in frail elders. American Journal of Physiology 277 (Endocrinology Metabolism 40): E135-E143, 1999. 8. Yamada, S., N. Buffinger, J. Dimario, et al. Fibroblast Growth Factor is stored in fiber extracellular matrix and plays a role in regulating muscle hypertrophy. Medicine and Science in Sports and Exercise 21(5): S173-180, 1989. 9. Frisch, H. Growth hormone and body composition in athletes. Journal of Endocrinology Investigation 22: 106-109, 1999. 10. Izquierdo, M., K Hakkinen, A. Anton, et al. Maximal strength and power, endurance performance, and serum hormones in middle-aged and elderly men. Medicine and Science in Sports Exercise 33 (9): 1577-1587, 2001. 11. Vermeulen, A., S. Goemaere, and J. M. Kaufman. Testosterone, body composition and aging. Journal of Endocrinology Investigation 22: 110-116, 1999. 12. Robergs, R. A. and S. O. Roberts. Exercise Physiology: Exercise, Performance, and Clinical Applications. Boston: WCB McGraw-Hill, 1997. 13. Kraemer, W. J., S. J. Fleck, and W. J. Evans. Strength and power training: physiological mechanisms of adaptation. Exercise and Sports Science Reviews 24: 363-397, 1996. 14. Carter, S. L., C. D. Rennie, S. J. Hamilton, et al. Changes in skeletal muscle in males and females following endurance training. Canadian Journal of Physiology and Pharmacology 79: 386-392, 2001. 15. Hakkinen, K., W. J. Kraemer, R. U. Newton, et al. Changes in electromyographic activity, muscle fibre and force production characteristics during heavy resistance/power strength training in middle-aged and older men and women. Acta Physiological Scandanavia 171: 51-62, 2001. 16. Schultz, E. Satelite cell behavior during skeletal muscle growth and regeneration. Medicine and Science in Sports and Exercise 21(5): S181-S186, 1989

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