WordNet

of or relating to or consisting of muscle; "muscular contraction"
having or suggesting great physical power or force; "the muscular and passionate Fifth Symphony"
abnormal enlargement of a body part or organ
undergo hypertrophy; "muscles can hypertrophy when people take steroids"

PrepTutorEJDIC

『助肉の』,筋肉でできた / 筋肉による / 筋肉の発達した
(生物体の部分・器官の)異常肥大,異常発達

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出典(authority):フリー百科事典『ウィキペディア（Wikipedia）』「2013/09/17 23:56:48」(JST)

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Athletes use a combination of strength training, diet, and supplementation to induce muscle hypertrophy.

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: myofibril and sarcoplasmic. Each of these specific types of muscle hypertrophy will result in increasing size of cells, but not of equal effect. Sarcoplasmic hypertrophy is focused on increasing the actual size of the muscle, and less on increasing strength. Myofibril hypertrophy will focus more on strength increase and less on an increase in the size of the skeletal muscle.

Hypertrophy stimuli[edit source | edit]

A range of stimuli can increase the volume of muscle cells. Summarizing, these changes occur as an adaptive response that serves to increase the ability to generate force or resist fatigue in anaerobic conditions.

Strength training[edit source | 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), while several repetitions (generally 8 – 12 for bodybuilding or 12 or more for muscular endurance) against a sub-maximal load facilitates mainly sarcoplasmic hypertrophy (professional bodybuilders and endurance athletes).^{[citation needed]} 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]} 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]}

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.

Anaerobic training[edit source | 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. 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]

Factors affecting hypertrophy[edit source | edit]

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.

Changes in protein synthesis and muscle cell biology associated with stimuli[edit source | edit]

Protein synthesis[edit source | 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]

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] 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.

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] 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]

Microtrauma[edit source | 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.

Myofibrillar vs. sarcoplasmic hypertrophy[edit source | edit]

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. 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.

In sports[edit source | edit]

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.

References[edit source | edit]

^ van Loon LJ, Goodpaster BH (2006). "Increased intramuscular lipid storage in the insulin-resistant and endurance-trained state". Pflugers Arch. 451 (5): 606–16. doi:10.1007/s00424-005-1509-0. PMID 16155759.
^ Soares JM (1992). "Effects of training on muscle capillary pattern: intermittent vs continuous exercise". The Journal of sports medicine and physical fitness 32 (2): 123–7. PMID 1279273.
^ Prior BM, Yang HT, Terjung RL (2004). "What makes vessels grow with exercise training?". J. Appl. Physiol. 97 (3): 1119–28. doi:10.1152/japplphysiol.00035.2004. PMID 15333630.
^ Bruusgaard JC, Johansen IB, Egner IM, Rana ZA & Gundersen K. (2010). Myonuclei acquired by overload exercise precede hypertrophy and are not lost on detraining. Proc Natl Acad Sci U S A 107, 15111-15116.
^ Manchester, K.L., “Sites of Hormonal Regulation of Protein Metabolism. p. 229”, Mammalian Protein [Munro, H.N., Ed.]. Academic Press, New York. p. 273.
^ Am J Physiol Regul Integr Comp Physiol. 2008 Jan;294(1):R172-8. Epub 2007 Nov 21. "Resistance training alters the response of fed state mixed muscle protein synthesis in young men." Exercise Metabolism Research Group, McMaster University, Hamilton, Ontario, Canada.
^ Miller B.F., Olesen J.L., Hansen M. et al. (2005) Coordinated collagen and muscle protein synthesis in human patella tendon and quadriceps muscle after exercise. J Physiol, 567, 1021-1033.
^ Symons, T. B.; Sheffield-Moore, M.; Wolfe, R. R.; Paddon-Jones, D. (2009). "A Moderate Serving of High-Quality Protein Maximally Stimulates Skeletal Muscle Protein Synthesis in Young and Elderly Subjects". Journal of the American Dietetic Association 109 (9): 1582–1586. doi:10.1016/j.jada.2009.06.369. PMID 19699838. edit
^ Bodybuilders and Protein – Part 2. Leehayward.com. Retrieved on 2011-06-19.
^ ^a ^b Tarnopolsky, MA; Atkinson, SA; MacDougall, JD; Chesley, A; Phillips, S; Schwarcz, HP (1992). "Evaluation of protein requirements for trained strength athletes". Journal of applied physiology (Bethesda, Md. : 1985) 73 (5): 1986–95. PMID 1474076.
^ Rankin, JW (2002). "Weight loss and gain in athletes". Current sports medicine reports 1 (4): 208–13. PMID 12831697.
^ . doi:10.1080/02640419108729866. Missing or empty |title= (help)
^ Di Pasquale, Mauro G. (2008). "Utilization of Proteins in Energy Metabolism". In Ira Wolinsky, Judy A. Driskell. Sports Nutrition: Energy metabolism and exercise. CRC Press. p. 79. ISBN 978-0-8493-7950-5.
^ http://www.unm.edu/~lkravitz/Article%20folder/musclesgrowLK.html
^ Kraemer, William J.; Zatsiorsky, Vladimir M. (2006). Science and practice of strength training. Champaign, IL: Human Kinetics. p. 50. ISBN 0-7360-5628-9.

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English Journal

The ion channels to cytoskeleton connection as potential mechanism of mechanosensitivity.

Martinac B.Author information Victor Chang Cardiac Research Institute, Darlinghurst, NSW 2010, Australia; St Vincent's Clinical School, University of New South Wales, Sydney, NSW 2052, Australia. Electronic address: b.martinac@victorchang.edu.au.AbstractAs biological force-sensing systems mechanosensitive (MS) ion channels present the best example of coupling molecular dynamics of membrane proteins to the mechanics of the surrounding cell membrane. In animal cells MS channels have over the past two decades been very much in focus of mechanotransduction research. In recent years this helped to raise awareness of basic and medical researchers about the role that abnormal MS channels may play in the pathophysiology of diseases, such as cardiac hypertrophy, atrial fibrillation, muscular dystrophy or polycystic kidney disease. To date a large number of MS channels from organisms of diverse phylogenetic origins have been identified at the molecular level; however, the structure of only few of them has been determined. Although their function has extensively been studied in a great variety of cells and tissues by different experimental approaches it is, with exception of bacterial MS channels, very little known about how these channels sense mechanical force and which cellular components may contribute to their function. By focusing on MS channels found in animal cells this article discusses the ways in which the connections between cytoskeleton and ion channels may contribute to mechanosensory transduction in these cells. This article is part of a Special Issue entitled: Reciprocal influences between cell cytoskeleton and membrane channels, receptors and transporters. This article is part of a Special Issue entitled: Reciprocal influences between cell cytoskeleton and membrane channels, receptors and transporters. Guest Editor: Jean Claude Hervé.
Biochimica et biophysica acta.Biochim Biophys Acta.2014 Feb;1838(2):682-91. doi: 10.1016/j.bbamem.2013.07.015. Epub 2013 Jul 23.
As biological force-sensing systems mechanosensitive (MS) ion channels present the best example of coupling molecular dynamics of membrane proteins to the mechanics of the surrounding cell membrane. In animal cells MS channels have over the past two decades been very much in focus of mechanotransduc
PMID 23886913

A role for Raptor phosphorylation in the mechanical activation of mTOR signaling.

Frey JW1, Jacobs BL1, Goodman CA1, Hornberger TA2.Author information 1Department of Comparative Biosciences, School of Veterinary Medicine, University of Wisconsin, Madison, 2015 Linden Dr., Madison, WI 53706, USA.2Department of Comparative Biosciences, School of Veterinary Medicine, University of Wisconsin, Madison, 2015 Linden Dr., Madison, WI 53706, USA. Electronic address: thornb1@svm.vetmed.wisc.edu.AbstractThe activation of mTOR signaling is necessary for mechanically-induced changes in skeletal muscle mass, but the mechanisms that regulate the mechanical activation of mTOR signaling remain poorly defined. In this study, we set out to determine if changes in the phosphorylation of Raptor contribute to the mechanical activation of mTOR. To accomplish this goal, mouse skeletal muscles were subjected to mechanical stimulation via a bout of eccentric contractions (EC). Using mass spectrometry and Western blot analysis, we found that ECs induced an increase in Raptor S696, T706, and S863 phosphorylation, and this effect was not inhibited by rapamycin. This observation suggested that changes in Raptor phosphorylation might be an upstream event in the pathway through which mechanical stimuli activate mTOR. To test this, we employed a phospho-defective mutant of Raptor (S696A/T706A/S863A) and found that the EC-induced activation of mTOR signaling was significantly blunted in muscles expressing this mutant. Furthermore, mutation of the three phosphorylation sites altered the interactions of Raptor with PRAS40 and p70(S6k), and it also prevented the EC-induced dissociation of Raptor from p70(S6k). Combined, these results suggest that changes in the phosphorylation of Raptor play an important role in the pathway through which mechanical stimuli activate mTOR signaling.
Cellular signalling.Cell Signal.2014 Feb;26(2):313-22. doi: 10.1016/j.cellsig.2013.11.009. Epub 2013 Nov 13.
The activation of mTOR signaling is necessary for mechanically-induced changes in skeletal muscle mass, but the mechanisms that regulate the mechanical activation of mTOR signaling remain poorly defined. In this study, we set out to determine if changes in the phosphorylation of Raptor contribute to
PMID 24239769

Fibulin-2 deficiency attenuates angiotensin II-induced cardiac hypertrophy by reducing transforming growth factor-β signalling.

Zhang H, Wu J, Dong H, Khan SA, Chu ML, Tsuda T.Author information *Nemours Biomedical Research and Nemours Cardiac Center, Nemours/Alfred I. duPont Hospital for Children, Wilmington, DE 19803, U.S.A.AbstractAngII (angiotensin II) is a potent neurohormone responsible for cardiac hypertrophy, in which TGF (transforming growth factor)-β serves as a principal downstream mediator. We recently found that ablation of fibulin-2 in mice attenuated TGF-β signalling, protected mice against progressive ventricular dysfunction, and significantly reduced the mortality after experimental MI (myocardial infarction). In the present study, we investigated the role of fibulin-2 in AngII-induced TGF-β signalling and subsequent cardiac hypertrophy. We performed chronic subcutaneous infusion of AngII in fibulin-2 null (Fbln2-/-), heterozygous (Fbln2+/-) and WT (wild-type) mice by a mini-osmotic pump. After 4 weeks of subpressor dosage of AngII infusion (0.2 μg/kg of body weight per min), WT mice developed significant hypertrophy, whereas the Fbln2-/- showed no response. In WT, AngII treatment significantly up-regulated mRNAs for fibulin-2, ANP (atrial natriuretic peptide), TGF-β1, Col I (collagen type I), Col III (collagen type III), MMP (matrix metalloproteinase)-2 and MMP-9, and increased the phosphorylation of TGF-β-downstream signalling markers, Smad2, TAK1 (TGF-β-activated kinase 1) and p38 MAPK (mitogen-activated protein kinase), which were all unchanged in AngII-treated Fbln2-/- mice. The Fbln2+/- mice consistently displayed AngII-induced effects intermediate between WT and Fbln2-/-. Pressor dosage of AngII (2 mg/kg of body weight per min) induced significant fibrosis in WT but not in Fbln2-/- mice with comparable hypertension and hypertrophy in both groups. Isolated CFs (cardiac fibroblasts) were treated with AngII, in which direct AngII effects and TGF-β-mediated autocrine effects was observed in WT. The latter effects were totally abolished in Fbln2-/- cells, suggesting that fibulin-2 is essential for AngII-induced TGF-β activation. In conclusion our data indicate that fibulin-2 is essential for AngII-induced TGF-β-mediated cardiac hypertrophy via enhanced TGF-β activation and suggest that fibulin-2 is a potential therapeutic target to inhibit AngII-induced cardiac remodelling.
Clinical science (London, England : 1979).Clin Sci (Lond).2014 Feb;126(4):275-88. doi: 10.1042/CS20120636.
AngII (angiotensin II) is a potent neurohormone responsible for cardiac hypertrophy, in which TGF (transforming growth factor)-β serves as a principal downstream mediator. We recently found that ablation of fibulin-2 in mice attenuated TGF-β signalling, protected mice against progressive ventricul
PMID 23841699

Japanese Journal

Molecular basis of muscle hypertrophy and atrophy : Potential therapy for muscular dystrophy

Ito Naoki,Miyagoe-Suzuki Yuko,Takeda Shin'ich
The journal of physical fitness and sports medicine : JPFSM : official journal of the Japanese Society of Physical Fitness and Sports Medicine 2(2), 179-184, 2013-05
NAID 40019655621

疾病予防・健康増進のための分子スポーツ医学(8)遺伝子ドーピング検出の技術創成をめざして : ミオスタチン遺伝子の発現操作による筋肥大のストラテジー,その検出,そして限界

武政徹
医学のあゆみ 244(7), 630-634, 2013-02-16
NAID 40019574932

How β2-adrenergic agonists induce skeletal muscle hypertrophy?

Kitaura Takashi
The Journal of Physical Fitness and Sports Medicine 2(4), 423-428, 2013
… Some β2-adrenergic agonists (β2-agonists) can strongly induce muscular hypertrophy, and are prohibited to use as doping drugs for athletes. … The pharmacological mechanism for such induced hypertrophy is not clear. … Muscular hypertrophy is most likely induced by way of protein synthesis via the IGF-1/PI3K/PKB system and negative myostatin pathway. …
NAID 130003388628