The acute and chronic effects of static stretching (SS) on joint range of motion (ROM) and stiffness of muscle-tendon unit (MTU) and/or muscle was reviewed. Previous studies have provided evidence that SS is effective in increasing ROM, both immediately and chronically. Moreover, 75 seconds (75s) SS is sufficient for eliciting an immediate, acute effect. In contrast, the recent trend is to evaluate the effect of stretching not by measuring ROM, but by measuring stiffness in order to eliminate the effect of psychological factors. However, the findings of studies measuring stiffness are conflicting, with some results indicating a decrease in stiffness and others indicating no change in stiffness despite changes in joint ROM. Our study results support that stiffness decrease with SS, and that >2 min of SS is effective in eliciting the effect. The retention time taken to achieve the effect of SS is also under discussion, and the retention time may differ for ROM and muscle stiffness. Concerning the chronic effect of SS, many studies have indicated that a routine SS program decreases passive torque or MTU and muscle stiffness. However, the underlying mechanism for this decrease remains to be clarified.

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Biological rhythms can be entrained by internal oscillatory processes and often become synchronized with each other. For integrated physiological systems, there is evidence to show that coupling can exist between cardiorespiratory and locomotor systems. Phase synchronization, which has been well documented in articles describing cardiac and locomotor rhythms for individuals engaged in rhythmic activity such as walking, running, or cycling, is called “cardiolocomotor synchronization” or “cardiolocomotor coupling”. Although this coupling has been hypothesized to play a functional role during exercise, the nature of this interaction, its physiological relevance, and the underlying mechanism behind this phenomenon are not fully understood. This review summarizes research findings to date on cardiolocomotor synchronization, and aims to provide the method for identification of phase synchronization between cardiac and locomotor rhythms. In addition, the mechanisms responsible for the synchronization and possible physiological function of this interaction are discussed.

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Microglia are one of the major glial cells in the brain implicated in the immune reactions in the central nervous system. Although the other major types of glial cells, astrocytes, oligodendrocytes and NG2 glia (or oligodendrocyte progenitor cells: OPCs) are all neuroectodermal cells, microglia are mesodermal macrophage-like cells. Because microglial cells have long been believed to be in the quiescent state in a normal mature brain, and to play no significant role, they have historically been called resting cells. However, it is currently accepted that such “resting” microglial cells with characteristic ramified morphology move their processes actively while surveying the microenvironment in the brain parenchyma. Still, the most prominent feature of microglial cells is their rapid activation in response to pathologic events including infection, inflammation, ischemia, trauma and neoplasms. Although microglia are normally neuroprotective cells, activated microglia in certain pathologic conditions are said to be a threat to neuronal survival by releasing potentially neurotoxic factors, such as glutamate, proinflammatory cytokines and reactive oxygen/nitrogen species, which aggravate neurological disorders by causing neuronal death. Microglial functions are affected by many kinds of endogenous substances such as neurotransmitters and corticosteroid hormones. Physical exercise may have the potential to suppress unfavorable activation of microglia in degenerative neurological disorders including Alzheimer’s disease and Parkinson’s disease by affecting neurotransmitters in the brain and serum level of the hormones.

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Mixed venous and arterial oxygen content (CvO₂ and CaO₂) are fundamental factors to connect cardiac output and oxygen uptake by the Fick principle. Direct measurements of CaO₂ and CvO₂ require blood samplings and quantifications of the oxygen contents. Arterial blood can be sampled from a peripheral artery, but a right cardiac catheter is necessary for mixed venous blood sampling. Moreover, quantifications of the blood oxygen contents are complicated compared with those of blood oxygen partial pressures. Accordingly, indirect methods to estimate CaO₂ and CvO₂ have been developed. CaO₂ can be evaluated as the sum of chemically and physically dissolved oxygen in arterial blood. If mixed venous blood is sampled, CvO₂ can be obtained from mixed venous oxygen saturation and partial pressure as well. As for noninvasive methods without blood samplings, arteriovenous oxygen difference (CaO₂ – CvO₂) was obtained from a relationship between respiratory exchange ratio and carbon dioxide partial pressure during rebreathing. Recently, we developed another noninvasive method to estimate CvO₂ from SpO₂ and heart rate with a pulse oximeter, and obtained an equation CaO₂ – CvO₂ (vol%) = –0.265×10^-6h² + 0.289×10^-3h + 7.74 with altitude h in meters. In this review, these two noninvasive methods, rebreathing and pulse oximeter, are discussed.

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In subjects with frailty syndrome, aging-related loss of muscle (sarcopenia) might progress to the extent that an older person loses his or her ability to live independently. Metabolic syndrome is a set of risk factors (abdominal obesity, insulin resistance, hypertension, and dyslipidemia) which markedly increases the risk of arteriosclerotic vascular disease. Due to the ongoing obesity pandemic and growing elderly population, frailty and metabolic syndromes are major emerging concerns in the healthcare system. Recent studies show that resistance training has remarkable beneficial effects on the musculoskeletal system including the prevention and treatment of these syndromes. Resistance training is probably the most effective measure to prevent and treat sarcopenia. With regard to the effect of resistance training on the muscular strength of elderly persons, the rate of improvement increases with intensity. Resistance training also has a favorable effect on metabolic syndrome since it decreases fat mass including abdominal fat, enhances insulin sensitivity, improves glucose tolerance, and reduces blood pressure values. Optimal nutrition enhances the anabolic effect of resistance training. Resistance training should be a central component of public health promotion programs along with aerobic exercise.

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Exercise has acute and chronic effects on fat burning. Concerning the acute effect, observed during and after a single exercise session, the enzymes responsible for burning fat increase. Carnitine palmitoyltransferase 1 (CPT1), which regulates the β-oxidation of fatty acids in mitochondria, is believed to play an important role in the acute effect. The activation of AMP-activated protein kinase (AMPK), which detects the energy state of muscles, may contribute to the exercise-induced activation of CPT1. In the chronic effect observed with ongoing exercise training, physiological changes in muscle function are seen. In particular, an increase in the number of mitochondria and enhancement of fatty acid metabolism are observed after endurance training. Peroxisome proliferator-activated receptor γ coactivator 1α (PGC-1α) plays an important role in adaptive thermogenesis and mitochondrial biogenesis. Exercise enhances the expression of PGC-1α, and the increase in PGC-1α mediates the physiological changes observed in skeletal muscle after endurance training. Recently, several isoforms of PGC-1α were identified. Different signaling pathways regulate the expression of each isoform. In this review, we discuss the regulation of lipid metabolism during physical activity. We also describe the PGC-1α isoforms and the signaling pathways that regulate their expression in relation to the effects of exercise training on skeletal muscle. Finally, we introduce two studies that may explain the systemic effect of endurance training.

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Skeletal muscle is the principal site of whole-body glucose, lipid, and energy metabolism, and several adaptive responses to physical exercise (muscle-contracting stimuli) by skeletal muscle contribute to whole-body health-promoting effects. Acute and/or repeated activation of skeletal muscle 5′AMP-activated protein kinase (AMPK) by physical exercise controls several metabolic adaptations. Thus, skeletal muscle AMPK is likely to be a “central molecule” that mediates anti-obesity/antidiabetes effects in response to physical exercise. Meanwhile, recent reports suggest that functional foods and their natural components (so-called phytochemicals) have anti-obesity/antidiabetes properties that stimulate skeletal muscle AMPK activity in a similar manner to physical exercise. For example, caffeine is a plant alkaloid that activates skeletal muscle AMPK and the activation mechanisms are exercise-like in terms of the association between α isoform-specific AMPK activation and the energy status. Furthermore, berberine, a component of natural medicines, resveratrol, a polyphenol found in red wine and other plant products, and caffeic acid, a coffee polyphenol, all stimulate AMPK activation in skeletal muscle accompanied by energy deprivation. In this study, we review our recent findings and related studies of the activation of AMPK by physical exercise and phytochemicals.

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In mammals, the circadian clock organizes physiological processes, including sleep/wake patterns, hormonal secretion, and metabolism, and regulates athletic performance. The circadian system is responsive to environmental changes such as light/dark cycles, food intake, and exercise. In this review, we will focus on the central and peripheral circadian molecular clock system, discussing how circadian rhythm affects athletic performance and muscle metabolism, and how exercise entrains the circadian rhythm. Importance of exercise training in rescuing circadian deficit–induced metabolic disorder is also discussed. The interaction of the circadian clock and exercise, called “chrono-exercise,” is poised to become an important research field of chronobiology.

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Quickness of response and movement speed are required for achieving athletic success in a variety of sports, and are often lost in various movement disorders. Because cognitive processes such as anticipation, attention, and planning are required for preparation of a quick motor response, we first introduce recent neurophysiological studies that have revealed brain activities underlying the preparation for movement, with some neurophysiological applications to improve motor quickness. Moreover, recent developments in the dynamical analysis of complex movements allow us to understand precise mechanisms and principles underlying fast multi-joint and multi-limb movements. We introduce our current theories on the mathematical analysis of complex movement coordination called induced acceleration analysis. We propose that movements are subject to both instantaneous and cumulative effects, which combine to integrate the torque and acceleratory forces on multiple joints. We also discuss evidence that movement rate has important effects on the coordination patterns, acting as a control parameter that determines organization of movement patterns. These findings underscore the necessity of conducting research on the science of movement that is highly interdisciplinary, including the fields of physiology, biomechanics, neurosciences, and behavioral sciences not only for the enhancement of sports performance, but also for the facilitation of motor recovery and rehabilitation from neurological damage.

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The present review aims to summarize current evidence regarding the intensity and amount of habitual physical activity required to obtain health benefits, in particular among middle-aged and older Japanese adults. In association with current technological advances, it has now become possible to assess the degree of habitual physical activity objectively using small activity monitors, such as pedometers and/or accelerometers. Three metabolic equivalents (METs) is widely accepted to be the appropriate intensity of habitual physical activity, and 30 to 60 minutes of daily physical activity at an intensity above three METs is considered to reduce the risk of lifestyle-related diseases in adults. Although interindividual variability in the appropriate number of steps is not small, these target levels generally correspond to 6,500-11,000 steps per day, and several studies have reported the clinical significance of 7,000-10,000 steps/day with respect to benefits on the immune function, muscle mass and prevention of metabolic syndrome. However, these target levels for the amount and intensity of habitual physical activity may be inadequate to maintain physical fitness, because the intensity of >3 METs is not guaranteed to induce exercise adaptability in all adults. Future research should therefore focus on the relative intensity identified according to the consensus intensity for safety and effectiveness, including the lactate threshold and/or percentage of maximal oxygen uptake under the free-living conditions, as well as fixed intensity exercise, such as that involving three or six METs.

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This review summarizes the regulation of cerebral blood flow (CBF) during stimulus-induced brain activation, mainly in functional near infrared spectroscopy (fNIRS) studies. fNIRS is less restrictive than other techniques for measuring brain activation, as it requires only a light burden to participants during measurements. Hence, fNIRS is used in multiple fields. On the other hand, fNIRS results are questionable due to the influence of various artifacts. Thus, we report the influence and countermeasures for important artifacts. Furthermore, we discuss about CBF regulation based on mechanisms at the cellular level, hemodynamic models suggested by functional magnetic resonance imaging (fMRI), and previous studies using simultaneous measurement with fNIRS and fMRI.

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The prevalence of diabetes in the population continues to increase worldwide. The complications of diabetes cause morbidity and mortality, and the cost of managing diabetes has become an important social problem in health economics. Strategies for the prevention and treatment of diabetes are therefore very important, and along with pharmacological and diet approaches, exercise plays a fundamental role. This review outlines the biological and clinical aspects of exercise therapy in patients with diabetes, and highlights the recent advances in research on this topic. The mechanisms by which exercise can reduce insulin resistance are described, along with the effects of exercise on plasma insulin and glucose levels, as well as on changes in muscle fiber types that occur in diabetes. Regarding clinical aspects of exercise in patients with diabetes, recent Japanese practice and physical activity guidelines are discussed, and the latest research into diabetes and exercise, including the role of myokines and the effects of exercise on lifespan and cognition are described.

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Sarcopenia is an age-related decline of skeletal muscle mass and function, leading to reduced physical ability and difficulties in carrying out day-to-day tasks; it has become a major health concern in our aging society. The exact etiology of sarcopenia is not completely understood, but recent studies have focused on age-associated changes in the neuromuscular junction (NMJ). Using an animal model of myasthenia gravis with antibodies against muscle-specific kinase (MuSK), a disorder of the NMJ characterized by muscle weakness, we investigated the role of the NMJ in the pathogenesis of sarcopenia. Our studies indicate that the structure and function of the NMJ is important for maintaining muscle mass and strength, which suggests that the malfunction of the NMJ plays a role, at least in part, in the onset of sarcopenia. These findings suggest that the NMJ will become an important therapeutic target for sarcopenia in the future.

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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.

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Previous studies have indicated that dynamic stretching acutely improves explosive performance, and dynamic stretching is now incorporated into warm-up protocols prior to sports activities that require explosive performance. The optimal protocol for dynamic stretching, however, has not been clarified. The purpose of this review is to clarify the optimal protocols for velocity and volume (i.e., repetition or distance x set) in dynamic stretching to improve explosive performance by systematic investigation. For velocity, the rate of change in explosive performance when dynamic stretching was performed “as fast as possible” (7.6 ± 3.8%) was significantly (P < 0.01) greater compared to when dynamic stretching was performed “without setting the velocity” (1.1 ± 5.3%). This finding suggested that dynamic stretching should be performed “as fast as possible”. As for volume, the repetition of dynamic stretching was significantly (P < 0.01) negatively correlated with the rate of change in explosive performance only when dynamic stretching was performed without setting the velocity. The distance of dynamic stretching was also significantly (P < 0.05) negatively correlated with the rate of change in explosive performance. These findings suggest that explosive performance might become impaired as the volume of dynamic stretching increases. By combining simple regression analysis of the repetition or the distance of dynamic stretching and the rate of change in explosive performance with a systematic investigation, it was found that the optimal “repetition” or “distance” x “set” of dynamic stretching was “10-15 repetitions” or “10 yards-20 meters” x “1-2 sets”, respectively.

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Cut-off values of habitual physical activity to determine mobility limitation (ML) would be useful for recommending modifications to life activities for community-dwelling older Japanese women. Accordingly, the aim of this study was to determine the levels of habitual physical activity (step counts: SC, moderate-vigorous physical activity: MVPA) capable of predicting ML in older women. This study included 630 community-dwelling older Japanese women (72.3 ± 5.9 years). ML was assessed in two consecutive self-reports, and defined as having some difficulty or being unable to walk one-quarter of a mile or climb 10 steps without resting. A uniaxial accelerometer continuously measured SC and MVPA for over 10 h/day for 7 days. Receiver operating characteristic analysis was conducted to determine the cut-off values of SC and MVPA that could predict ML. Results show that the prevalence of ML in this study was 28.3% (n = 178). The optimal cut-off values of SC and MVPA for predicting ML were 5,773 steps/day (sensitivity: 66.3%, specificity: 70.8%) and 107.4 min/week (sensitivity: 84.8%, specificity: 55.3%). It was concluded that the levels of SC and MVPA capable of predicting ML were 5,773 steps/day or 107.4 min/week for older Japanese women. Although these levels of habitual physical activity would be useful as an indicator in modifying the life activities in older Japanese women, the validity of the cut-off values for predicting ML will need to be confirmed in longitudinal studies.

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In the present study, the aim was to determine whether a history of ankle sprain during the junior (JUN; age < 12 years) playing years of soccer players could predict the occurrence of ankle sprain in their junior youth (JY; age < 13, 14, and 15 years) playing years. Therefore, we administered a questionnaire survey to 1,361 players belonging to 28 JY soccer teams. Analyses of the participants’ answers indicated that 57.0% of the players sustained ankle sprains during their JUN playing years and 64.0% of the players sustained ankle sprains during their JUN and JY playing years. Players with a history of ≥5 ankle sprains had a higher occurrence rate of sprains in their JY years as compared to players with no history of ankle sprains. The odds ratio (OR), calculated using logistic regression analysis based on the number of ankle sprains sustained during the JUN playing years, was highest for players with ≥5 sprains compared to those with 2 or 3 sprains during the JUN playing years. To reduce the occurrence rate of ankle sprains for players in the JY category, effective screening processes, prevention measures, and rehabilitation programs for ankle sprains during the JUN playing years should be established.

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This cross-sectional study was performed to determine the relationship between the intensity of daily physical activity (PA) assessed by triaxial accelerometer (ACCtri) and muscle strength or gait speed. We measured the hand grip strength (HGS) and knee extension strength (KES) as well as preferred gait speed (PGS) and maximal gait speed (MGS) of a total of 178 community-dwelling elderly men aged 70-79 years. The duration and intensity of PA were evaluated by ACCtri on eight consecutive days, and the total duration of each level of activity intensity (Inactivity, Light PA: LPA, Moderate PA: MPA, and Vigorous PA: VPA) and daily step count were also measured. After adjustment for age, body mass index (BMI) and body fat percentage, KES and MGS were significantly correlated with step count. The duration of MPA was correlated with KES (r = 0.208, P < 0.01) and MGS (r = 0.213, P < 0.05). PGS and HGS were not significantly correlated with any PA parameters. MPA and step counts were significantly, but weakly, related to KES and MGS. The results suggest that a longer time spent on either daily ambulatory activity or MPA may be associated with age-associated loss of muscle strength (dynapenia) and gait decline in older men.

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