著者

Yasuro Furuichi Nobuharu L. Fujii

出版者

一般社団法人日本体力医学会

雑誌

The Journal of Physical Fitness and Sports Medicine (ISSN:21868131)

巻号頁・発行日

vol.6, no.5, pp.311-316, 2017-09-25 (Released:2017-09-29)

参考文献数

51

被引用文献数

4

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Skeletal muscle stem cells, known as satellite cells, participate in postnatal skeletal muscle growth, regeneration, and hypertrophy. They are quiescent in the resting state, but are activated after muscle injury, and subsequently replicate and fuse into existing myofibers. The behavior of satellite cells during muscle regeneration is regulated by extrinsic factors, such as the extracellular matrix, mechanical stimuli, and soluble factors. Myokines, muscle-derived secretory factors, are important regulators of satellite cell activation, proliferation, and differentiation. It is well known that muscle injury induces the release of various growth factors from myofibers, and these growth factors affect satellite cells. It has recently been shown that myokines secreted from myofibers without cell damage also regulate satellite cell functions. Here, we summarize myokines with known roles in the regulation of satellite cells and the mechanism underlying this regulatory process.

著者

Shoko Nishizono Zi Wang Yukari Watanabe Yoshihisa Ohata Takuya Chiba

出版者

一般社団法人日本体力医学会

雑誌

The Journal of Physical Fitness and Sports Medicine (ISSN:21868131)

巻号頁・発行日

vol.6, no.4, pp.201-207, 2017-07-25 (Released:2017-07-12)

参考文献数

44

被引用文献数

2

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More than 80 years ago, McCay and colleagues first reported that limiting the amount of food provided to experimental animals (i.e. calorie restriction or CR) prolongs their lifespan and suppresses the onset and progression of various age-related diseases. Today, CR remains the most reliable method of delaying aging in experimental animals, and research into its underlying molecular mechanisms is ongoing. CR has been reported to have anti-aging and life-extension effects on primates, with progress being made toward applications for humans. Studies on mechanisms underlying the onset and prevention of lifestyle-related diseases such as diabetes have elucidated the cellular signaling pathways that regulate energy metabolism, and commonalities have been discovered between the targets of existing diabetes drugs and the signaling pathways affected by CR. This finding has led to research into the discovery of drugs that have the anti-aging effects of CR in the absence of food intake limitations, namely CR mimetics (CRM). Several drugs have been reported to extend the lifespan of experimental organisms, which may thus have the potential to also extend human lifespan. In this article, we outline and compare those drugs that have been reported to date and discuss the possibility of taurine as a CRM, which is a topic of our ongoing research.

著者

Takashi Fukuda Sekiya Koike Syumpei Miyakawa Hiroto Fujiya Yuki Yamamoto

出版者

一般社団法人日本体力医学会

雑誌

The Journal of Physical Fitness and Sports Medicine (ISSN:21868131)

巻号頁・発行日

vol.6, no.4, pp.241-249, 2017-09-25 (Released:2017-07-12)

参考文献数

41

被引用文献数

3

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The aim of this study is to understand the head impact during actual collisions between American football players from Japanese universities. The subjects of this study were 23 players who belonged to T university in the Kantoh Collegiate American Football Association Division 2. We used a Vector Mouthguard (i1 Biometrics Inc.) equipped with 6 degrees of freedom (DOF) to measure the head linear acceleration (LA) and rotational acceleration (RA) as well as the head injury criterion (HIC), impact location, and number of impacts during collisions. The average number of collisions per player during a practice and during a game was 14.3 and 15.7, respectively. In terms of positions, the ratio (1:1.3) of total number of impacts for backs to linemen in Japan is lower than that (1:3) in the USA. Both during the games and practices, the range of 10 g < X ≤ 15 g in the average peak LA values was the most frequent, and the distributions were largely skewed toward low values (p < 0.05). The medians during the games and practices were 16.77 g and 15.87 g, respectively. The number of collisions during practices in Japan was significantly higher than that in the USA. Particularly, linemen undergo more head collisions than those of backs. Another common factor is that the impact of head collision during a game is significantly higher than that during a practice. However, data on Japanese university players is limited, and further data collection should be done before determining an accurate estimate of the practical concussion risk threshold.

著者

Kotaro Tamura Yasuro Furuichi Yasuko Manabe Nobuharu L. Fujii

出版者

一般社団法人日本体力医学会

雑誌

The Journal of Physical Fitness and Sports Medicine (ISSN:21868131)

巻号頁・発行日

vol.6, no.2, pp.89-93, 2017-03-25 (Released:2017-03-19)

参考文献数

41

被引用文献数

1

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Satellite cells are resident muscle stem cells located between the basal lamina and the plasma membrane of myofibers. They play crucial roles in muscle growth during the postnatal stage and muscle regeneration following postnatal development. However, the roles of satellite cells in adult muscles - in muscle growth, function, and adaptation - are poorly understood. Recently, by studying genetically engineered mice with conditionally ablated satellite cells, it has been reported that satellite cells play important roles in muscle growth and maintenance of muscle spindles or neuromuscular junctions, and produce growth factors that affect other organs. Here, we review the recent studies using tamoxifen-inducible Pax7-DTA mice and describe the novel roles of satellite cells in the maintenance of skeletal muscle plasticity.

著者

Amrudha Mohan Atsushi Asakura

出版者

一般社団法人日本体力医学会

雑誌

The Journal of Physical Fitness and Sports Medicine (ISSN:21868131)

巻号頁・発行日

vol.6, no.2, pp.65-74, 2017-03-25 (Released:2017-03-19)

参考文献数

123

被引用文献数

9

---

Regeneration of muscle is undertaken by muscle stem cell populations named satellite cells which are normally quiescent or at the G0 phase of the cell cycle. However, upon signals from damaged muscle, satellite cells lose their quiescence, and enter the G1 cell cycle phase to expand the population of satellite cell progenies termed myogenic precursor cells (MPCs). Eventually, MPCs stop their cell cycle and undergo terminal differentiation to form skeletal muscle fibers. Some MPCs retract to quiescent satellite cells as a self-renewal process. Therefore, cell cycle regulation, consisting of satellite cell activation, proliferation, differentiation and self-renewal, is the key event of muscle regeneration. In this review, we summarize up-to-date progress on research about cell cycle regulation of myogenic progenitor cells and muscle stem cells during embryonic myogenesis and adult muscle regeneration, aging, exercise and muscle diseases including muscular dystrophy and muscle fiber atrophy, especially focusing on cyclin-dependent kinase inhibitors (CDKIs).

著者

Isao Muraoka Yuko Gando

出版者

一般社団法人日本体力医学会

雑誌

The Journal of Physical Fitness and Sports Medicine (ISSN:21868131)

巻号頁・発行日

vol.1, no.3, pp.447-455, 2012-09-25 (Released:2012-10-23)

参考文献数

51

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The present article reviews the effects of the traditional “live high-train high” (LHTH) protocol and the contemporary “live high-train low” (LHTL) protocol on physiological adaptations and on athletic performance at sea level based on results from studies in which athletes were assigned to an “altitude group” and “sea level group”. Consequently, the LHTH protocol and LHTL protocol were considered to provoke nearly similar physiological adaptations. On the other hand, the LHTL protocol appeared to be more effective than the LHTH protocol with respect to endurance performance at sea level. Furthermore, the LHTL protocol is suggested to possibly be effective for sprinting events as well. These results indicate that the LHTL protocol affords about 1 to 4% improvement in exercise of approximately 30-second to 17-minute duration. However, a recent meta-analysis suggested that the LHTH protocol improves the maximal power output of elite athletes. Furthermore, it is conceivable that interindividual differences greatly affect the results obtained from altitude training. Therefore, there is an urgent need to elucidate interindividual differences that are involved in physiological adaptations to hypoxic environments or improvements in athletic performance. Moreover, the relevant elucidation will require the adjustment of altitude (oxygen concentration), daily duration of exposure, and length of stay in concert with individual features. In some cases, a decision about whether or not to adopt the LHTL or LHTH protocol would be necessitated. In addition, the combination of the intermittent hypoxic training protocol with the LHTL protocol will require a detailed investigation.

著者

Mitsutoshi Kurosaka Shuichi Machida

出版者

一般社団法人日本体力医学会

雑誌

The Journal of Physical Fitness and Sports Medicine (ISSN:21868131)

巻号頁・発行日

vol.1, no.3, pp.537-540, 2012-09-25 (Released:2012-10-23)

参考文献数

32

被引用文献数

1 1

---

Skeletal muscle injury is generally caused by stimuli, such as intense resistance training, eccentric muscle contraction, muscle strain and bruising. Injured skeletal muscles are repaired within several weeks after injury, because skeletal muscle has a remarkable capacity for muscle regeneration. Cellular and molecular events underlying the regenerative processes are mainly regulated by myogenic stem cells and inflammatory cells. The aim of this review is to summarize the current understanding of the cellular and molecular mechanisms responsible for muscle regeneration. In this review, focus will be given to the critical roles of satellite cells and macrophages during muscle regeneration. In addition, the satellite cell responses to exercise are also discussed.

著者

Norio Motohashi Matthew S. Alexander Louis M. Kunkel

出版者

一般社団法人日本体力医学会

雑誌

The Journal of Physical Fitness and Sports Medicine (ISSN:21868131)

巻号頁・発行日

vol.1, no.1, pp.151-154, 2012-05-25 (Released:2012-08-22)

参考文献数

42

被引用文献数

2

---

Skeletal muscle is the most abundant tissue in the mammalian body and is composed of multinucleated fibers that contract to generate force and movement. In addition, skeletal muscle has the ability to regenerate following severe damage by exercise, toxins or disease. Regeneration is possible because of the presence of mononucleated precursor cells called satellite cells. After injury, satellite cells are activated, proliferate, and fuse with the damaged fibers or fuse together to form new myofibers. A fraction of satellite cells self-renew and behave as muscle stem cells. Although satellite cells are the main players in muscle regeneration, a number of other cell types are also recruited to form new fibers or to modulate the behavior of satellite cells. Here we present an overview of current knowledge of regeneration focusing on muscle satellite cells and other stem cells and discussing promising stem cell therapy for diseases such as muscular dystrophy.

著者

Minenori Ishido

出版者

一般社団法人日本体力医学会

雑誌

The Journal of Physical Fitness and Sports Medicine (ISSN:21868131)

巻号頁・発行日

vol.1, no.4, pp.675-677, 2012-11-25 (Released:2012-12-28)

参考文献数

27

---

Adult mammalian skeletal muscles possess a stem cell population, called muscle satellite cells. Satellite cells mainly contribute to restoring damaged or diseased muscles. The migration of satellite cells plays an important role in muscle regeneration, and it has been traditionally thought that satellite cell migration is regulated by lamellipodial/filopodial formation. In addition, it has recently been thought that blebbing/amoeboid formation plays an important role in satellite cell migration. On the other hand, the method/mechanism(s) of the migration of satellite cells located within skeletal muscles in vivo has barely been elucidated. However, because, in recent years, in vivo real-time imaging of satellite cell migration in skeletal muscles has been reported, it is expected to markedly expand our understanding of satellite cell migration in vivo. This review will focus on the regulatory mechanism of satellite cell migration in vitro and new insights into in vivo satellite cell mobility using real-time imaging.

著者

Yusuke Ono

出版者

一般社団法人日本体力医学会

雑誌

The Journal of Physical Fitness and Sports Medicine (ISSN:21868131)

巻号頁・発行日

vol.3, no.2, pp.229-234, 2014-05-25 (Released:2014-05-24)

参考文献数

45

被引用文献数

1 6

---

Satellite cells are skeletal muscle tissue stem cells located between the basal lamina and sarcolemma of myofibres and play crucial roles in adult muscle repair and regeneration as well as postnatal muscle growth. More and more findings indicate that satellite cells exist as a genetically and functionally heterogeneous population among muscles, which is not only based on fibre types, but also embryonic origin. Satellite cells are also a heterogeneous population even within a single myofibre. Only a small population of satellite cells possesses “stemness” and exhibits remarkable regeneration with a high self-renewal ability when transplanted into injured muscles. Recent studies have shed light on the cellular and molecular characteristics of satellite cell heterogeneity including Pax7+Myf5- cells, satellite-side population cells, Pax7-nGFPhigh cells, and slow-dividing cells. Here, we review recent progress in our understanding of the heterogeneity and stem cell hierarchies in the satellite cell population.

著者

Wataru Mizunoya

出版者

一般社団法人日本体力医学会

雑誌

The Journal of Physical Fitness and Sports Medicine (ISSN:21868131)

巻号頁・発行日

vol.4, no.3, pp.259-270, 2015-07-25 (Released:2015-07-27)

参考文献数

90

被引用文献数

4

---

The contractile and metabolic properties of skeletal muscle depend on muscle fiber type composition. There are two major fiber types: type 1 fibers (slow-twitch oxidative) and type 2 fibers (fast-twitch glycolytic). Muscle fiber type is a critical physiological property that affects sports performance and metabolic ability. To date, natural food components have not been regarded as regulators of skeletal muscle fiber type. Meanwhile, in the present century, it has been revealed that several nuclear receptors (NRs) and their cofactors affect skeletal muscle fiber type independently from muscular contraction. Interestingly, many compounds from natural food sources have been identified as NR ligands. These facts indicate the possibility of the regulation of muscle fiber type by food components. In this review, we present an overview of the current knowledge of the role of NRs and their cofactors in skeletal muscle fiber type and discuss the perspective of muscle fiber type regulation by food components via NR.

著者

Mizuno Koh

出版者

The Japanese Society of Physical Fitness and Sports Medicine

雑誌

The Journal of Physical Fitness and Sports Medicine (ISSN:21868131)

巻号頁・発行日

vol.3, no.3, pp.307-315, 2014

被引用文献数

5

---

This review introduces a variety of human circadian rhythms including physiological processes and mental and physical performances, with reference to real-life situations. Circadian rhythms play a role in physiological processes, such as core body temperature and plasma melatonin, which are recognized as the body clock. As humans are diurnal organisms, mental performance declines primarily at night, secondarily in the early afternoon; this is consistent with risks of traffic and industrial accidents. Physical performance is composed of various fitness components and generally reaches its peak and nadir at around evening and early morning, respectively. Exceptions to this are body balance control and accuracy, both of which require brain function. Although maximal oxygen consumption (VO₂ max) measured in the laboratory shows a constant value independent of the time of day, actual endurance capacity might be determined by core body temperature at the beginning of exercise, thermoregulatory response, and environmental temperature and humidity, all of which vary with the time of day. As the most powerful factor affecting the human circadian clock is bright light, physical exercise may be one factor entraining the human circadian pacemaker. However, experimental evidence has suggested that exercise itself has little or no influence on shifting the human master clock. Although further studies are required, recent studies have demonstrated that physical exercise at a certain time of day specifically improves physical performance at the same time, which might be independent of the master clock.

著者

Nishijima Takeshi Kita Ichiro

出版者

The Japanese Society of Physical Fitness and Sports Medicine

雑誌

The Journal of Physical Fitness and Sports Medicine (ISSN:21868131)

巻号頁・発行日

vol.4, no.3, pp.253-258, 2015

被引用文献数

5

---

Populations worldwide are increasingly becoming physically inactive, which is related to somatic and psychological health problems that are prevalent in modern society. Recent epidemiological studies have indicated that the associations between physical inactivity and depression are bidirectional. Numerous animal studies have demonstrated that exercise improves hippocampal function. Because the hippocampus is a pivotal brain region that exerts inhibitory control over stress responses by affecting the hypothalamus-pituitary-adrenal axis, enhanced hippocampal function by exercise can increase stress resilience, which helps prevent stress-related depression. In contrast, physical inactivity is difficult to model in animal studies, and little is known about the effects of physical inactivity on the rodent hippocampus. To fill this gap, we previously developed a mouse model of habituated voluntary wheel running cessation as a reverse intervention to control physical activity. We found that reducing physical activity by cessation of wheel running impairs hippocampal neurogenesis in mice. Thus, this review discusses the relevant literature and provides a hypothesis that physical inactivity can be a potential risk factor for stress-related depression as it increases stress vulnerability by impairing hippocampal function.

著者

Shigeru Yamada Eriko Kizaki Aya Ozeki Mio Nakagawa Hitomi Fujita

出版者

一般社団法人日本体力医学会

雑誌

The Journal of Physical Fitness and Sports Medicine (ISSN:21868131)

巻号頁・発行日

vol.4, no.3, pp.287-294, 2015-07-25 (Released:2015-07-27)

参考文献数

29

被引用文献数

1

---

Sarcopenia from aging, inactivity, weightlessness, disease and malnutrition causes social problems due to associated physical dysfunction, a decrease in QOL, and risk of death. As a means of alleviating sarcopenia, appropriate exercise and nutrition therapy is required. However, nourishment therapy is especially important for a person in a situation where exercise is not feasible for maintaining skeletal muscle mass and muscular strength. Therefore, the authors studied the inhibitory effect of aspartic acid magnesium on disuse muscle atrophy. Herein we have described two of the mechanisms of action of aspartic acid magnesium on disuse muscle atrophy suppression. Initially, inactivity causes a decrease in capillary and oxygen supply, inhibits ATP synthesis, and produces active oxygen. As a result, the proteolysis system is activated and muscle atrophy progresses. We have described the effect of aspartic acid magnesium uptake on this mechanism, and the imbalance of the intracellular mineral with the inactive proteolysis system. The above is the content of this review.

著者

Satoshi Shibuya Satoshi Unenaka Yukari Ohki

出版者

一般社団法人日本体力医学会

雑誌

The Journal of Physical Fitness and Sports Medicine (ISSN:21868131)

巻号頁・発行日

vol.4, no.2, pp.213-216, 2015-05-25 (Released:2015-05-28)

参考文献数

32

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We perceive that our body belongs to us and is a coherent and unified entity. Therefore, body-ownership is fundamental to self-consciousness. To explore body-ownership in normal subjects, researchers have intensively used a bodily illusion known as the rubber hand illusion (RHI). This review article focuses on RHI studies. In a standard RHI paradigm, the sight of the participant’s hand is occluded, while a life-sized fake hand is visible. Synchronous stroking of the fake and real hands with paintbrushes elicits a subjective sensation that the fake hand is their own. The RHI is generally demonstrated using a self-report questionnaire as a subjective measurement, and proprioceptive drift (i.e., mislocalization of the real hand toward the fake hand) as an objective measurement. There are two constraints for inducing the RHI: visuo-tactile synchrony and consistency between multisensory inputs and body representations. The RHI can also be induced by visuo-motor correlations: viewing movements of the rubber hand that are synchronous with movements of the real hand. In this RHI variant, participants experience body-ownership as well as agency, which is a type of bodily self-consciousness that one is initiating and controlling his/her own actions. Neuroimaging studies suggest that the RHI is associated with a wide range of neural substrates, including fronto-parietal networks. In sum, accumulating evidence from the RHI suggests that body-ownership is very flexible, and the brain can incorporate a non-corporal object into a person’s own body.

著者

Yu Kitaoka Yukari Endo Kazutaka Mukai Hiroko Aida Atsushi Hiraga Hideo Hatta

出版者

一般社団法人日本体力医学会

雑誌

The Journal of Physical Fitness and Sports Medicine (ISSN:21868131)

巻号頁・発行日

vol.3, no.4, pp.451-456, 2014-09-25 (Released:2014-10-02)

参考文献数

33

被引用文献数

2 11

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We examined the muscle glycogen, and muscle and plasma lactate concentrations before and after 1 and 2 min of intensive exercise at 120% VO2max, and examined possible relationships between these indexes and protein levels of monocarboxylate transporters (MCT) in the gluteus medius muscle of Thoroughbred horses. The horses underwent 1 and 2 min of intensive exercise at the speed of 120% maximal oxygen consumption (VO2max) on a treadmill. The plasma lactate concentration increased after 1-min exercise (11.7 ± 0.8 mmol/L) and 2-min exercise (23.1 ± 1.1 mmol/L). The muscle lactate concentration increased after 1-min exercise (17.3 ± 2.1 mmol/kg) and 2-min exercise (23.6 ± 2.0 mmol/kg). While there was no significant difference in lactate accumulation in the plasma between the first minute and the second minute, lactate accumulation in muscle significantly decreased in the second minute compared with the first minute. The muscle glycogen level decreased after both 1- (42%) and 2-min (41%) exercise, but there was no difference between the levels after 1- and 2-min exercise. The muscle lactate concentration after 2-min intensive exercise positively correlated with the protein level of MCT4 (r = 0.78, p < 0.01). These results suggest that glycogen breakdown occurs in the first minute of intensive exercise, and Thoroughbred horses with higher muscle lactate production during exercise are endowed with higher expression of MCT4, that facilitates the efflux of lactate from muscle cells.

著者

Shinya Masuda Hisashi Takakura Hisashi Kato Tetsuya Izawa

出版者

一般社団法人日本体力医学会

雑誌

The Journal of Physical Fitness and Sports Medicine (ISSN:21868131)

巻号頁・発行日

vol.3, no.4, pp.435-439, 2014-09-25 (Released:2014-10-02)

参考文献数

57

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A number of changes occur with aging in skeletal muscles including a reduction in muscle fiber size and fiber number. However, recent studies have indicated that the elderly tend to be more resistant to fatigue than the young, particularly during prolonged isometric muscle contraction. In this review, we explore the molecular mechanisms in muscle cells that are involved in this phenomenon. Aging has been thought to induce preferential loss of fast-type fibers. However, previous studies have shown that a fiber-type shift with aging is specific to the region, type and/or function of the muscles. Aging promotes the production of reactive oxygen species (ROS) in skeletal muscle, and ROS is suggested to activate AMP-activated protein kinase (AMPK). AMPK signaling is involved in muscle atrophy, and it activates peroxisome proliferator-activated receptor gamma coactivator 1-alpha (PGC-1α). PGC-1α is considered a key regulator of mitochondrial biogenesis, and furthermore, it could be involved in the reinnervation of muscle fibers that have been denervated due to aging. Thus, the balance between AMPK and PGC-1α could play an important role in increasing fatigue resistance in aged skeletal muscle.

著者

Katsuhiro Koyama

出版者

一般社団法人日本体力医学会

雑誌

The Journal of Physical Fitness and Sports Medicine (ISSN:21868131)

巻号頁・発行日

vol.3, no.1, pp.115-120, 2014-03-25 (Released:2014-03-20)

参考文献数

46

被引用文献数

1 14

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Physical exercise-mediated production of reactive oxygen species has been shown to cause oxidative stress, particularly in contracting skeletal muscles. Growing evidence indicates that exercise-induced oxidative stress plays an indispensable role in upregulating signaling pathways required to promote not only skeletal muscle, but also whole body adaptation to physical exercise. It is becoming increasingly clear that exercise-related beneficial adaptations are strongly regulated by exercise-induced oxidative stress, consistent with hormesis theory. According to the hormesis hypothesis, exercise-induced mild to moderate oxidative stress through reactive oxygen species generation stimulates favorable exercise-related physiological adaptations. Additionally, repeated exposure to oxidative stress induced by physical training can trigger various hormesis-based adaptations (i.e., hormetic adaptive responses), including activation of antioxidative defense mechanisms. This brief review provides an overview of several conceptual frameworks related to exercise-mediated hormetic adaptive responses rather than a detailed critique of individual reports.

著者

Shizuo Sakamoto Masayuki Konishi Hyeon Ki Kim Naoya Endoh Masaki Takahashi Syun Takagi Taishi Midorikawa

出版者

一般社団法人日本体力医学会

雑誌

The Journal of Physical Fitness and Sports Medicine (ISSN:21868131)

巻号頁・発行日

vol.1, no.3, pp.499-504, 2012-09-25 (Released:2012-10-23)

参考文献数

17

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There have been several reports on exercise prescriptions and the effects of exercise on various diseases, particularly for fat metabolism disorder. In recent years, notably from the latter half of the 1990s, studies on effective exercise prescriptions for fat metabolism disorder have taken into account the type of exercise content (type, intensity and duration per session) that has beneficial effects on fat metabolism disorder and the post-exercise recovery period. These studies have analysed the fat oxidation rate as a parameter for examining the beneficial effects of exercise on fat metabolism disorder. In this review, studies, undertaken in Japan and overseas, are introduced that are related to exercise and the fat oxidation rate.

著者

Yasuko Manabe Shouta Miyatake Mayumi Takagi

出版者

一般社団法人日本体力医学会

雑誌

The Journal of Physical Fitness and Sports Medicine (ISSN:21868131)

巻号頁・発行日

vol.1, no.1, pp.51-58, 2012-05-25 (Released:2012-08-22)

参考文献数

89

被引用文献数

2 9

---

Skeletal muscle has only recently been considered a secretory organ. Muscle-derived proteins are now termed myokines. Until date, about 20 proteins known as cytokines, growth factors, and adipokines have been reported as myokines. However, only a few studies have been able to demonstrate secretion from the skeletal muscle. Furthermore, many reports are still uncertain of whether proteins are secreted from skeletal muscle cells or from the surrounding tissue, because some studies have measured myokine concentration in blood taken from human and animal subjects, which also contains other organ-derived proteins. Secretion of some myokines is promoted by muscle contraction or insulin stimulation, whereas others seem to be constitutively secreted. The mechanisms of action and roles of myokines are also complicated. Some are believed to affect distant organs through endocrine and paracrine mechanisms, while others affect organs through an autocrine mechanism. In this article, we review updates of myokines, including their history. Furthermore, the article discusses the need to re-define myokines in order to avoid possible misunderstandings because of insufficient data.