Breathing during exercise is an important physiological function for maintaining homeostasis of hydrogen ion concentration ([H+]) in the internal environment. In general, ventilatory response during exercise is considered to be automatically (unconsciously) controlled depending on exercise intensity and the corresponding perturbation of neurohumoral factors. However, in awake humans, the act of performing physical exercise is coupled with conscious elements such as motivation, effort, and emotions. This means that ventilatory control during exercise is also inseparably linked to such mental processes. With regard to the indivisibility between ventilatory control and conscious elements, there has been increasing psychological and neurophysiological evidence supporting the importance of mental and behavior factors in addition to neurohumoral factors. Therefore, in this paper, previous studies, on the indivisibility of ventilatory control and conscious elements, were looked at, and the roles of mental processes in ventilatory control and [H+] homeostasis during exercise discussed.
The latest neuroscience studies have reported that physical activity and exercise can change the levels of brain monoamines and neurotrophic factors, increase synaptic plasticity and neurogenesis, and alter intracellular signaling proteins and neuronal activity. These studies have considered that physical exercise might be associated with psychological health such as stress reduction, antidepressant/anxiolytic properties, and improvement in mood through morphological and functional alterations of the central nervous system involved in emotion regulation. Although evidence of the neural and behavioral benefits of physical exercise is accumulating, the neural mechanisms behind these beneficial effects and emotion regulation from physical exercise are not clearly understood. This paper discusses how physical activity and exercise regulate emotional functions such as stress responses, mood, and depression or anxiety, focusing on specific areas of the brain involved in emotion regulation.
In this review, focus is given to the cognitive brain functions associated with motor learning and the control of learned motor behavior, as revealed by non-invasive studies in humans. After providing a definition of motor control and learning, the tasks adopted in previous studies are first introduced, and some important findings about motor behavior and pertinent theoretical models are described. Relying mainly on findings from the event-related potential (ERP) technique, but also from neuroimaging, this review focuses on motor learning and motor control in skilled action, with an emphasis on movement preparation and performance monitoring.
White adipose tissue (WAT) is located beneath the skin as subcutaneous adipose tissue (SAT), around internal organs as visceral adipose tissue (VAT), pericardial and epicardial adipose tissue, and inside muscles in human beings. Recent studies indicate that developmental and patterning genes are differentially expressed in SAT and VAT, and some of these genes exhibit changes in expression that closely correlate with the extent of obesity and pattern of fat distribution. Furthermore, the development of adipocytes from mesenchymal stem/progenitor cells is thought to be mediated by developmental signaling molecules including nodal, Wnt/wingless (Wg), bone morphogenetic proteins (BMPs), fibroblast growth factors (FGF), and others. Of these, BMPs and the FGF family have been suggested to play a role in maintaining energy homeostasis. However, it remains unclear whether these developmental and patterning genes are associated with morphological changes in WAT in response to exercise training (TR). On the other hand, when TR reduces the number of adipocytes in WAT, it increases preadipocyte factor 1 mRNA expression but down-regulates peroxisome proliferator-activated receptor-γ mRNA expression in stromal-vascular fraction cells, including adipose tissue-derived stromal cells, via the up-regulation of hypoxia-inducible factor-1α, which may also up-regulate the mRNA expression of vascular endothelial growth factor-A and its receptor. The purpose of this review is to summarize the research to date on the morphology of WAT and adipose tissue cellularity in exercise adaptation.
Even a small daily positive energy balance leads to weight gain over a period of a few years. Understanding changes in the energy balance is important for preventing obesity. The purpose of this review is to discuss the variable factors involved in total daily energy expenditure (TDEE) in humans. TDEE comprises the resting metabolic rate (RMR), diet-induced thermogenesis (DIT), and physical activity energy expenditure (PAEE). RMR comprises the largest component (~60%) of TDEE. DIT accounts for approximately 10% of TDEE, and PAEE approximately 30%. A large part of the variation in RMR can be explained by body composition and body size. The primary determinant of DIT is meal size and composition. Body size and aging are also potential factors of variability in DIT. PAEE can be further categorized into exercise-induced energy expenditure (EXEE) and non-exercise activity thermogenesis (NEAT). EXEE mainly depends on body size, and exercise intensity and duration. In addition, excess post-exercise oxygen consumption following exercise is thought to have a significant impact on total EXEE. Based on a review of published studies, however, it is clear that in most individuals, EXEE is not a large contributor to TDEE. On the other hand, NEAT has the greatest impact on variation in TDEE, which varies by up to 2000 kcal per day between people of similar body size. In summary, there are several factors involved in the contribution of each component of TDEE. Although each factor contributes to small changes in TDEE, the sum of these influences may induce a large energy imbalance.
Over the last decade, extensive progress has been made with regard to our understanding of the molecules that regulate skeletal muscle regeneration. Satellite cells are muscle-specific stem cells located under the basal lamina of muscle fibers, which are responsible for muscle regeneration. This precise coordination of complex stem cell responses throughout adult life is regulated by evolutionarily conserved signaling networks that cooperatively direct and control. This process includes the activation, proliferation, and differentiation of stem cells. This highly regulated process of tissue regeneration recapitulates embryonic organogenesis with respect to the involvement of interactive signal transduction networks. Indeed, various modulators such as insulin-like growth factor-I (IGF-I), hepatocyte growth factor (HGF), and leukemia inhibitory factor (LIF) have been shown to stimulate the activation and proliferation of satellite cells. PI3K (phosphatidylinositol 3-kinase)/Akt/mTOR (mammalian target of rapamycin), calcineurin, and serum response factor (SRF) seem to contribute to muscle regeneration by regulating differentiation of satellite cells. In contrast, myostatin inhibits these processes through forkhead box O (FOXO) and/or SMAD 2/3-dependent signaling. In this review, the recent findings for muscle regeneration are described.
While urate is an important anti-oxidant molecule in the body, high plasma levels of urate cause morbidity including urate crystal deposition in joints (gout) and stone formation in the urinary tract. Because urate is an end product of purine metabolism, it must be excreted from the body via the kidneys or intestinal tract. Despite its low water solubility, this negatively charged molecule cannot permeate the cell membrane without specific proteins called transporters. In the kidney proximal tubule, the relatively urate-specific transporters, URAT1 and URATv1, serve as a urate reabsorptive path, while the broad specific transporters, OAT1/3 and NPT1/4, are utilized for urate secretion. For sports medicine audiences, renal hypouricemia and exercise-induced acute renal failure resulting from URAT1 or URATv1 mutation may be of interest. URATv1 seems to play a role in urate transport into blood from the liver, a major organ for urate production, and ABCG2 is critical for urate excretion into the intestine. Many of these transporters have been identified by genome-wide association studies (GWASs) linking high plasma urate levels and/or gout to single nucleotide polymorphisms (SNPs) in these transporter genes. While GWASs are a very powerful approach in searching for genes associated with disease, cell biological and physiological characterization of candidate gene products is critical for elucidation of (patho) physiology.
Multipotent stem cells, other than satellite cells, that can give rise to primary myoblasts postnatally, are present in the interstitial spaces of skeletal muscle. These stem cells show differentiation potential into mesodermal and ectodermal cell lineages, and, thus, are called skeletal muscle interstitium-derived multipotent stem cells (Sk-MSCs). They are Pax7- at initial isolation; and colony-forming units of these cells typically include non-adherent type myogenic cells, while satellite cells are known to be adherent in cell culture. In these colonies, both Pax7- and Pax7+ myogenic cells are produced depending on asymmetric cell division. A large number of myotubes are also formed in each colony associated with putative Pax7+ satellite cells. Interestingly, Pax7-/non-adherent myogenic cells showed basal lamina (BL) formation during cell culture, whereas Px7+ myogenic cells did not. In in vivo analysis, interstitial myogenic cells showing BL formation were detected at early stages of myogenesis in the compensatory enlarged muscle, while myogenic cells in the parent fiber BL cylinder, probably satellite cells, did not form BL. Production of BL, associated with satellite cells, is essential for the in vivo establishment of new muscle fiber formation in the interstitium with, of course, innervation and capillary supply. Thus, the multipotency of Sk-MSCs that can give rise to peripheral nerve and vascular-related cells, such as Schwann cells, perineurial cells, endothelial cells, pericyte, and vascular smooth muscle cells, may have advantages over satellite cells. Therefore, the physiological role of Sk-MSCs, as a source for postnatal new muscle fiber formation (hyperplasia) and extension of nerve-vascular networks following growth and/or severe heavy resistance exercise, needs to be further investigated.
Static and dynamic exercise is accompanied by increases in arterial blood pressure, heart rate and sympathetic nerve activity. It has been hypothesized that these cardiovascular responses are mediated by central command as well as by feedback mechanisms operating via afferent nerves (group III and IV fibers) that arise from skeletal muscles, are sensitive to mechanical (the so-called muscle mechanoreflex) and metabolic changes (the so-called muscle metaboreflex), and are modulated by arterial and cardiopulmonary baroreflexes. In this review, discussion is focused on the roles of the arterial baroreflex and muscle metaboreflex in cardiovascular regulation during exercise. In the first part of the review, brief discussion is made of the functions of these two reflexes during exercise; in the second part, their interactions are looked at in more detail. It is thought that during heavy exercise, the arterial baroreflex and the muscle metaboreflex are both activated, and interact in ways that lead to modulation of the primary cardiovascular reflex responses. Two types of interaction have been demonstrated. In the first, the arterial baroreflex acts to oppose pressor responses induced via the muscle metaboreflex. The second type of interaction involves the modulation of arterial baroreflex function during muscle metaboreflex activation. The authors offer commentary on these two types of interaction, including recent knowledge.
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.
Japan is one of the most rapidly aging countries in the world. “Healthy Japan 21” is a Japanese government initiative promoting lifestyle-related disease prevention, health promotion, and successful aging. Increasing physical activity participation among older Japanese, the least physically active of any age group, is especially important for preventing frailty and chronic disease, and the associated health care expenditure. Informed by the research we have to date, the following evidence-based conclusions can be drawn relative to exercise and physical activity for the obese population. A combination of aerobic exercise, resistance exercise and physical activities, in addition to proper diet (mostly caloric restriction: 1200 kcal for women and 1680 kcal for men for a certain period of time), is more effective than either form of intervention alone for reducing body weight, visceral fat, blood pressure, and many other negative health-related variables. Exercise habituation in conjunction with proper diet is also most effective for improving vital age. Incorporating and adhering to these lifestyle factors, coupled with adherence to other known health modifiers (reduced stress, improved sleep, etc) will help reduce individual and population obesity and improve national health.
The mean number of steps taken by a person, per day in Japan, has decreased significantly over the past 10 years to approximately 1000 steps a day; and the number of people that exercise regularly, among the working population between 20 and 60 years of age, is also decreasing. Such reductions in physical activity and regular exercise are of great concern regarding the health of the Japanese. Healthy Japan 21 (2nd series), a new measure being launched in 2013, will set goals for individuals, such as “increase the number of steps taken,” and “increase the percentage of people that exercise regularly”, as well as goals for regions and municipalities, such as “increase the number of cities facilitating physical activities” and “support municipalities working to improve an active environment”. At present, to enhance physical activity among the Japanese population, the Exercise and Physical Activity Reference (EPAR) for Health Promotion 2006 is being revised to include directions for setting new references of physical activity (including exercise) in leisure time for the elderly, expressed in an easy to understand manner, such as by number of steps or duration of activity, e.g., “let's move our body 10 min more a day”. Healthy Japan 21 (2nd series) and the new EPAR for health promotion should be utilized to involve a variety of social resources for improving physical activity and exercise habits of the Japanese.
Skeletal muscles have defensive and regenerative systems to protect them from severe injury and/or fiber degeneration. Several stresses, including muscle-contraction during exercise and heat stress, induce the specific proteins named heat shock proteins (HSPs) or stress proteins. Many studies have shown that HSPs protect muscle from injury or stimulate repair of injured muscles. Injured or degenerated skeletal muscle fibers have the potential to recover to normal size and function. This regenerative ability of muscle fibers largely depends on a specific cell known as the satellite cell, which is located between the basal lamina and plasma membrane of the muscle fibers. Satellite cells are well known as muscle-specific stem cells and play crucial roles in muscle hypertrophy and fiber regeneration by activation, proliferation, differentiation, and fusion to the existing fibers, or by forming new myotubes in new growing fibers. This review focuses on the functional roles of heat shock proteins and also on the fiber regeneration process with activation of satellite cells in skeletal muscles.
The thermoregulatory system interacts vitally with the body fluid regulatory system. Thermoregulatory response during heat stress, such as sweating and cutaneous vasodilation, stimulates body fluid regulatory response by elevating plasma osmolality and reducing central blood volume. Isotonic hypovolemia, or baroreceptor unloading, and plasma hyperosmolality, in turn, inhibit thermoregulatory response to heat stress, suggesting that body fluid regulation is given priority over thermoregulation. On the other hand, osmoregulatory vasopressin secretion and thirst are augmented by elevated body core temperature. Heat acclimation enhances thermoregulatory response to heat stress. Adaptation of the body fluid regulatory system, such as increased plasma volume and reduced osmotic inhibition of thermoregulatory response, is possibly involved in the mechanism for the enhancement of thermoregulatory response to heat stress by heat acclimation. In this review, we discuss the interaction between body fluid regulation, especially osmoregulation, and thermoregulation mainly in humans.
Physical activity surveillance at a population level is important. The National Health and Nutrition Survey of Japan has been carried out annually, and two kinds of assessments for physical activity are included in the survey: total step counts per day, measured by a pedometer, and questions on exercise habits. From peak values seen in 1998 - 2000, time trends display a decline of age-adjusted mean steps per day, and the average percentage of regular exercisers has increased only in the age group of 50 years old or higher. As for standard or target values of physical activity, the Dietary Reference Intakes (DRIs) for Japanese presents standard values of physical activity levels (total energy expenditure divided by basal metabolic rate) for each gender and age group. The moderate value of physical activity level for adults is 1.75. Furthermore, the Exercise and Physical Activity Guide for Health Promotion 2006 (Exercise Guide 2006) was released based on the “Exercise and Physical Activity Reference for Health Promotion 2006” (EPAR2006). The reference values were set as 23 MET-hours/week for physical activity and 4 MET-hours/week for exercise. The former value is equivalent to 8000 to 10000 daily steps. Thus, Japan has established target values for physical activity and exercise habits, and daily steps have been investigated in the Japanese population. However, the target or standard values of physical activity are not sufficiently linked to the nationwide surveillance of actual levels of physical activity. Therefore, development of physical activity evaluation methods for Japanese is necessary.
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.
Contraction-induced compromise of muscle function and, in the extreme, muscle damage has been linked to loss of Ca2+ homeostasis and resultant sustained elevation of intracellular Ca2+ ([Ca2+]i). Against a background of in vitro approaches, a novel in vivo model permits investigation of the impact of different contraction types (e.g., isometric, ISO; eccentric, ECC) on [Ca2+]i accumulation profiles. [Ca2+]i elevation of ECC-contracted muscle is more rapid and greater in magnitude compared to ISO. Stretch-activated channels (SAC) are responsible, in large part, for this ECC contractions-induced [Ca2+]i elevation. Transient Ca2+ accumulation in the cytosol incurs loss of force production, whereas continuous high levels of [Ca2+]i, especially following ECC contractions, lead to muscle damage, including disrupted sarcomeres and membranes, and proceed, subsequently, to muscle regeneration via apoptosis and necrosis.
This review provides evidence for the task-, intensity-, and duration-specific modulation of twitch, spinal, corticospinal and cortical responses recorded up to ~18 min after the end of a muscle contraction produced by artificial and voluntary muscle activation in animal and human experimental models. Animal data revealed facilitation in spinal excitability after tetanic contraction; a phenomenon confirmed by human experiments using artificial, as well as voluntary, activation of muscle. There is evidence for a strong task-specific potentiation of spinal excitability associated with shortening and high intensity isometric contractions in contrast to depression after lengthening contractions. Contraction duration-specific effects suggest that when a contraction is performed to fatigue, post-exercise spinal excitability tends to decrease. Data from a limited number of transcranial magnetic brain stimulation studies suggest that, akin to spinal excitability, voluntary muscle contraction produces corticospinal and cortical excitability-associated changes. Of possible functional relevance, concerning these data, is that potentiation and depression in neural excitability can shape the mechanisms of how acute responses to exercise accumulate and convert to chronic adaptations. Of clinical relevance is that an even better understanding of the post-contraction effects would provide the opportunity for therapists to set exercise parameters according to the goals of therapy and need of patients and athletes to up/ down-regulate spinal, corticospinal, and cortical activity.
This is a brief review of recent evidence concerning the influences of respiratory muscle fatigue on the circulatory response to exercise, endurance exercise performance and associated peripheral locomotor muscle fatigue. Inspiratory muscle fatigue enhances muscle sympathetic vasomotor outflow and blood pressure during exercise. As a consequence, blood flow and oxygen transport to the working limbs are reduced, and this exacerbates the development of peripheral muscle fatigue and compromises endurance performance. These effects are relevant for healthy humans performing high intensity endurance, and, even at mild intensities, for patients with pulmonary disease and heart failure.
Adipose tissue is an important site for energy storage and energy homeostasis. In addition, it has been recognized as an endocrine organ that produces and secretes a number of bioactive peptides or proteins called “adipokines”. These molecules are directly and indirectly involved in the pathogenesis of metabolic disorders, such as obesity, type 2 diabetes, cardiovascular diseases, and metabolic syndrome. Until now, a number of adipokines (e.g. adiponectin, leptin, tumor necrosis factor-α interleukin-6, and retinol-binding protein-4) have been identified and their functions have been elucidated. Among these, adiponectin is known to be involved in improvement in insulin sensitivity and endothelial function, and promotion of fat oxidation. Aerobic exercise also has the same effects. The benefits of aerobic exercise could be induced through changes in adiponectin levels. In this short-review, focus is given to the effects of aerobic exercise on circulating adiponectin levels in humans.
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.
Cardiovascular disease is a major cause of death in many developed countries. Impaired clearance of postprandial triacylglycerol has been associated with an increase in cardiovascular disease risk. Physical activity can reduce many cardiovascular disease risk factors including postprandial triacylglycerol concentrations. Public health guidelines suggest that physical activity can be accumulated in several short bouts throughout the day, with a minimum duration of 10 minutes per activity bout. Until recently, limited evidence was available to support the effect of accumulating physical activity on postprandial lipaemia. Thus, the authors conducted a series of investigations to examine the influence of accumulated physical activity on postprandial lipaemia. The implications of the research findings are discussed in keeping with practical guidance for those wishing to engage in exercise that will lower postprandial triacylglycerol concentrations.
Humans sequentially perceive spatial information surrounding them when performing intended motor movements. Precise spatial information is constructed in the brain by integrating sensory information such as visual, vestibular, and somatosensory inputs. Visual input is considered an essential source of stable spatial perception in our daily lives. In addition, and in parallel with visual function, vestibular and somatosensory systems have important roles in spatial perception, particularly when unconscious. Although the vestibular system is not considered one of the “five senses” of human sensation, this system serves a couple of important functions. One important function is the prompt stabilization of the head and body against outer disturbances. In addition, vestibular signals are utilized in the higher order of the brain for construction of three-dimensional spatial perception. In this review, the functional properties, as well as the neural system, of the vestibular system are introduced in relation to spatial perception.