Vertebrate skeleton consists of numerous pieces of bone and cartilage, each placed at the appropriate anatomical site by an elaborate regulatory process in developmental patterning. In this process, mesenchymal cells initially form aggregates at the respective anatomical sites. These aggregates later generate chondrocytes that form a cartilage anlagen and further differentiate into hypertrophic chondrocytes in the growth plate cartilage that is replaced by bone through endochondral bone formation. In an alternative pathway, skeletogenic mesenchymal progenitor cells directly generate osteoblasts through an intramembranous bone formation process. In recent decades, considerable studies have been performed to understand the molecular mechanisms of these processes. By reviewing recent studies, the author attempts to address how the critical transcription factors and secreted factors regulate skeletal tissue formation. Emphasis is placed mainly on the in vivo functions of transcription factors Sox9, Runx2, and Osterix, and signaling exerted by secreted molecules such as Bone morphogenetic proteins (BMPs), Transforming growth factor β (TGF-β), Wnts, Fibroblast growth factors (FGFs), Indian hedgehog (Ihh), and Parathyroid hormone-related protein (PTHrP). Each of these factors is essential for the proper progression of skeletal tissue formation. Elucidation of the mechanisms that govern differentiation of skeletal cells would further contribute to our understanding of maintenance and diseases of skeletal tissue.
Oxygen (O2) transport from air to mitochondria depends on both the mechanisms of convection and diffusion. In the final step of the O2 cascade, from the capillary to myocyte, O2 is transported into cells via diffusion according to the potential differences in PO2 across plasma membranes. Myoglobin (Mb), an important cellular O2 binding protein that is expressed in skeletal and cardiac muscle cells, has been known as an O2 store or O2 transporter for more than half a century. However during the last decade, Mb functions have been re-assessed as a result of further knowledge gained from Mb-deficient mice that suggest other functions beyond its function as an O2 store. At first glance, Mb-deficient mice do not show any superficial physiological deficits. However, homeostatic mechanisms, including increased capillary density that tends to steepen the PO2 gradient to the mitochondria, effectively shorten the diffusion path for O2. Recent research demonstrated that Mb is releasing its binding O2 at onset of muscle contraction to manipulate intracellular O2 content. The O2 gradient Mb substantially contributes to nitric oxide homeostasis, and could interact with substrates such as fatty acid. This recent experimental evidence will help us to refine our understanding of Mb physiological function and establish a basis for further research.
A number of familial and twin studies have assessed the relative contribution of genetic and environmental factors to physical performance or its-related traits and have estimated that there is a significant genetic component to their phenotypes. In addition, aerobic capacity has been found to have stronger maternal inheritance than paternal. This finding implies that functional differences in maternally inherited mtDNA-encoded proteins involved in oxidative phosphorylation affect aerobic performance. In this article, therefore, we focus on associations between mtDNA polymorphisms/haplogroups and elite Japanese athlete status. From sequencing analysis of the control region in the mtDNA, certain mtDNA polymorphisms and haplogroups were shown to be associated with elite Japanese endurance athlete status, probably due to enhanced ATP production by mitochondria in the cardiac and skeletal muscles or both. This phenomenon is in agreement with several previous reports on Caucasian and African populations. It should be noted that certain mtDNA polymorphisms or haplogroups are also associated with elite Japanese sprint athlete/power status, probably due to enhanced calcium dynamics in the skeletal muscle. Thus, mtDNA polymorphisms/haplogroups influence not only aerobic performance but also anaerobic performance.
To maintain an erect posture, sensory information must be integrated from the vestibular, visual, and somatosensory systems. Additional somatosensory cues from the fingertips have been proposed to be able to improve postural stability during quiet standing. The present review paper focuses on the beneficial effect of light fingertip touch on postural control during quiet standing as follows: 1) First, the fundamental light touch procedure for the improvement of postural stability is introduced. 2) The effects of light touch on postural stability in instable persons, including elderly adults, infants, and patients with bilateral vestibular loss, congenital blindness, and somatosensory loss by diabetic neuropathy, are described, indicating that postural stability improves due to multisensory reweighting when a light touch stimulus is applied. 3) The relation between muscle activity and postural sway by light touch are described, demonstrating that the cross-correlation function between velocity information on the center of mass and the activity of the gastrocnemius muscle is stronger with somatosensory input by light touch than without it. 4) The effects of noise-like mechanical stimulation to the fingertips on postural stability are described based on the concept of stochastic resonance, which further enhances postural stability. The literature emphasizes that the effects of light touch on postural stability are purely caused by somatosensory information and not due to the mechanical support provided by the fingers. 5) In contrast to active touch, the efficacy of passive touch is summarized with respect to negligible friction between the skin and a touch device, leading to a decline in postural sway. 6) Finally, the effects of light touch in temporal relation to light touch, muscle activity, and postural sway, are interpreted, taking into consideration that light touch is effective for postural stability in many individuals, including patients with neuropathy, visual disorders, and diabetes.
Global warming is now recognized worldwide. Thermoregulation is critical for human survival when exposed to a severely hot environment. Thermoregulation is closely related to physical fitness, but fitness decreases with advancing age. Thus, thermoregulatory functions also decline with age. In fact, several major heat waves have occurred around the world in the last 10 years, and the mortality ratio was further elevated in elderly people. We encourage exercise training in the elderly to maintain physical fitness, but we should also recognize how human thermoregulation alters with aging. The primary role of thermoregulatory functions is to maintain the internal body temperature within a narrow range. Internal body temperature is regulated by the thermal balance between heat production and heat dissipation. Older individuals have relatively low heat production, impaired thermal perception, and reduced autonomic and behavioral thermoregulatory responses. However, these diminished thermoregulatory functions can be improved, although the gain is lower or limited relative to their younger counterparts. We summarize thermoregulatory functioning in elderly people based on recent publications and our findings.
Cells sense mechanical force and their physical environment to change their fate and behavior through mechanotransduction. The mechanotransduction is, by translating mechanical forces and deformations into biochemical intracellular signaling, changing gene expressions and adjusting cellular and extracellular structure. Given that mechanosensitive signaling modulates cellular functions as diverse as proliferation and differentiation, such signaling is crucial for normal tissue development and homeostasis. Here we review current evidence for the mechanical regulation of cell differentiation, specifically in musculoskeletal tissues, such as skeletal muscle, fat, bone, and cartilage.
In the present review, we include a series of recent experiments in order to update and summarize the characteristics of ball spin in baseball pitching. The motion of a ball thrown by a pitcher is influenced by three forces: gravity, the drag force due to air resistance, and the lift force which deflects a ball vertically or laterally due to the Magnus effect (Magnus force). The forces acting on a baseball are influenced by the ball's translational speed and spin rate as well as the orientation of the spin axis. The lift force acting on the ball becomes greater with increases in the “spin parameter” (proportion of the spin rate and the movement speed) when the spin axis of the ball is orthogonal to the direction of movement. On the other hand, when the spin axis is located in line with the direction of the movement (so-called “gyro ball”), the drag force becomes smaller and the lift force decreases to nearly zero regardless of the spin parameter. The orientation of the spin axis also affects the direction of the lift force on the ball; that is, the lift force acts perpendicular to the cross product of the spin axis and the direction of motion. There are great variations in the spin of fastballs; both spin rate and orientation of the spin axis vary widely across individual pitchers. When the spin rate is extremely low, such as with a knuckle ball, the amount and direction of lift force changes irregularly during flight. This is caused by seams on the ball surface, which cause an unpredictable “fluttering” trajectory. The reason for the success of pitchers that can produce abnormal or unique ball spins is discussed.
The gastrointestinal tract secretes several peptide hormones that regulate food intake by transmitting signals to the central nervous system related to energy homeostasis. Abnormalities in the regulation of food intake are manifested as overeating or refusal of food (apastia) that can cause obesity, leanness, and other metabolic disorders. Obesity, in particular, is the root cause of various lifestyle diseases, and, therefore, is a major health problem that should be overcome. Eating disorders are considered to be caused by a breakdown in the food intake regulatory system of the central nervous system and the peripheral nervous system; much is still unknown about signal transmission, and the secretion of gastrointestinal peptides and their receptor mechanisms. However, studies have shown that amylin, glucagon, insulin, pancreatic polypeptide, and enterostatin secreted by the pancreas function as food intake suppressors in peripheral tissues. In addition, leptin excreted by adipocytes is also known to function as a food intake suppressor. This review focuses on the gastrointestinal peptides that are related to food intake. This issue introduces anorexic peptides, cholecystokinin, peptide YY, glucagon-like peptide-1 (GLP-1), bombesin/gastrin-releasing peptide (BN/GRP), or oxyntomodulin (OXM), and orexigenic peptide ghrelin. Moreover, it also summarizes how these peptides function to maintain homeostasis in an organism.
The ability of the respiratory motor system to adapt to various functional demands is very important for maintaining human lifestyles. Age-related changes in the system have been studied in several animals. Furthermore, many kinds of models of altered use have been developed to examine activity-related changes in the system. In this review, the plasticity of the respiratory motor system, including spinal phrenic motoneurons and endplates on muscle fibers are discussed, mainly relating to inactivity and over-activity models in rat diaphragm muscle.
Lactate is a dynamic substrate that has great potential as an energy source. During exercise, lactate is transported out of contracting muscle cells and is oxidized by the heart and oxidative types of muscles. The diffusion of monocarboxylates, such as lactate and pyruvate, across the plasma membranes of mammalian cells is facilitated by a family of integral membrane transport proteins called monocarboxylate transporters (MCTs). Currently, 14 unique members of the MCT family have been identified. In skeletal muscle, 2 isoforms with different kinetic properties, MCT1 and MCT4, are expressed and have been identified as key transporters regulating lactate flux across the plasma membrane. MCT1 is primarily expressed in oxidative fibers, in which lactate can be used as fuel for mitochondrial oxidation, and is closely associated with the rate of lactate uptake. MCT4 is highly expressed in glycolytic fibers and may be responsible for the removal of lactate produced by glycolysis. Rapid changes in the expression of MCT1 and MCT4 can occur in response to acute exercise, the regulation of which may involve transcriptional and post-transcriptional mechanisms. Increased MCT expression may be the primary factor enhancing the rate of lactate flux. However, the molecular regulatory mechanisms by which exercise upregulates MCT expression in muscle are not yet fully understood. It is important to understand how exercise regulates MCT expression so that training programs can be designed to increase the muscle oxidative disposal of lactate.
Respiratory chambers are the current gold standard for assessing human energy expenditure and substrate utilization over a long period of time (several hours to several days), based on oxygen consumption, carbon dioxide production, and urinary nitrogen excretion. Analysis of human energy metabolism using a respiratory chamber provides information about the total energy expenditure (TEE), sleeping metabolic rate (SMR), resting metabolic rate, diet-induced thermogenesis (DIT), activity-induced thermogenesis (AIT), and substrate oxidation. In this review, we describe the theoretical underpinnings of the respiratory chamber, as well as the measurement reproducibility and applications as study endpoints for indirect calorimetry. In humans, the coefficients of variation in energy expenditure and substrate utilization were estimated by 24-h repeatability studies. Under the appropriate conditions, the coefficients of variation for TEE were 1% to 5%, SMR was around 1%, DIT was around 40%, AIT was around 10%, and substrate oxidation was around 5%. Factors that impact energy expenditure and substrate oxidation have been reported, and future weight changes can be predicted based on the 24-h respiratory quotient and substrate oxidation. As the 24-h energy expenditure and substrate oxidation are affected by the 24-h energy balance, it is important to consider the subject's energy balance prior to and during calorimetry. Accurate measurements of energy and substrate balance (intake minus utilization) will contribute to a better understanding of the conditions that lead to changes in body weight. Properly obtaining measurements using a respiratory chamber requires a thorough understanding of the measurement principles and calculation methods, as well as an appropriate protocol.
Pituitary growth hormone (GH) and insulin-like growth factor-1 (IGF-1) play a critical role in the regulation of postnatal organ growth and overall body size. IGF-1 has been indicated as a very effective anabolic agent, and thus considered a critical regulator of skeletal muscle hypertrophy in response to increased workload such as resistance exercise. In contrast, recent studies using a genetic model of IGF-1/IGF-1 receptor have indicated that functional IGF-1-dependent mechanisms are not an absolute requirement for growth/hypertrophy in mature skeletal muscle. In this brief review, classic and recent aspects in hormonal/growth factor-dependent regulation of skeletal muscle mass are discussed. This review will particularly focus on 1) functional requirements of IGF-1 regulation in skeletal muscle hypertrophy and 2) cellular mechanisms in the regulation of protein synthesis in skeletal muscle.
Reduction of carotid arterial compliance and endothelial dysfunction are associated with advancing age and cardiovascular diseases. From the viewpoint of exercise physiology, exercise can be divided into that with aerobic components and that with resistance components. It is widely accepted that arterial compliance and endothelial function are improved by aerobic exercise training. On the other hand, it has been reported that resistance training decreases arterial compliance, but has no effect on endothelial function. In addition, according to research, combined aerobic and resistance training did not affect arterial compliance, which suggests that simultaneously performed aerobic training may negate and prevent the reduction in arterial compliance induced by resistance training. Considering the favorable effects of aerobic and resistance training on cardiorespiratory fitness and muscular strength, the author concludes it is necessary to perform both aerobic and resistance training to maintain and improve vascular and whole-body health.
In 2006, Rankinen et al. reported 127 candidate obesity-related genes, and since then more have been identified (http://www.genome.gov/gwastudies/). A lot of mutations in more than 7 genes, especially in the MC4-R gene, were reported as monogenic obesity (primarily related to the regulation of appetite). Many candidate genes related to polygenic obesity were reported in genome-wide association studies (GWAS) that compared the frequency of single-nucleotide polymorphisms (SNPs) between normal and obese individuals. There are numerous genes related to appetite control, glucose and lipid metabolism, as well as energy metabolism. Recently, it was reported that obesity and lifestyle-related diseases may be induced epigenetically. Specifically, the food intake and degree of exercise in childhood, together with the food intake of both parents, affect whether the offspring is likely to become obese in adulthood. Although the interplay between specific genes and molecules that are linked to obesity is gradually being elucidated, there is little evidence to suggest they are suitable targets for therapeutic intervention. Understanding obesity and lifestyle-related diseases at the molecular level will undoubtedly be helpful. Nonetheless, it is also important to confirm the nature of the disease for each individual. Adequate and timely intervention, by giving sound advice, will improve the health of individuals regardless of genetic risk factors.
Studies on exercise-induced stimulation of glucose uptake into skeletal muscle have indicated that components of the insulin signal transduction system, such as insulin receptor, IRS-1, and PI 3-kinase, are not involved in the mechanism of glucose uptake elicited by an acute bout of exercise, suggesting that the underlying molecular mechanism, by which an acute bout of exercise increases glucose uptake, is distinct from that of insulin. Sedentarism, maturation and dietary factors such as high-fat feeding cause insulin resistance, which is a result of defective signal transduction. On the other hand, exercise training and calorie restriction improve and prevent insulin resistance. The exercise training effects represented by improved insulin action in vivo are chiefly attributed to changes in body composition factors such as increased muscle volume and decreased body fat, and changes in post-insulin receptor mechanisms.
The aim of this study was to investigate the effects of one night of sleep deprivation on maximal fat oxidation during a graded exercise test. Ten healthy young males underwent two 2-day control and sleep deprivation trials. Participants were allowed normal sleep from 2300 to 0700 for the control trial, whereas they were required to stay awake for 34 h during the sleep deprivation trial. At 1700 on day 2, participants performed a graded exercise test to exhaustion on a treadmill; this allowed us to determine maximal oxygen uptake and maximal fat oxidation. Before and immediately after the graded exercise test, blood samples were collected in order to measure glucose, insulin, free fatty acid, and triglyceride concentrations. Plasma glucose concentrations were significantly higher in the sleep deprivation trial than in the control trial before the graded exercise test. Serum insulin and free fatty acid concentrations were not significantly different between the two trials. Serum triglyceride concentrations were significantly lower in the sleep deprivation trial than in the control trial. The maximal fat oxidation rate, oxygen uptake, and heart rate at maximal fat oxidation intensity, during the graded exercise test, were not significantly different between the two trials. These findings suggest that maximal fat oxidation during graded exercise is unaffected by one night of sleep deprivation.
Few exercises that encourage elderly persons to be physically active have been proved to exhibit both method-effectiveness (efficacy) and use-effectiveness (effectiveness) in a long-term setting. We recently developed a square-stepping exercise (SSE) for elderly persons and assessed its effects on adherence and functional fitness in a long-term, observational setting following a randomized controlled trial (RCT). Sixty-eight people (SSE group, n = 32; walking group, n = 36) participated in a 3-month RCT. At the end of the RCT period, they were encouraged to continue the assigned exercise autonomously. We measured adherence to the assigned exercise for a total of 4 years and their functional fitness after 1 and 4 years. Functional fitness measurements at each follow-up point and at the 3-month intervention entry were compared in terms of method-effectiveness (per-protocol based [PPB]) and use-effectiveness (intention-to-treat [ITT]). At the 1-year and 4-year follow-ups, 69% and 63%, respectively, of the SSE group had continued performing the assigned exercise. These values were comparable to those of the walking group (65% and 65%). From the PPB and ITT analyses, we found that SSE was as effective—or more effective—than walking with regard to functional fitness. In conclusion, SSE is a good exercise choice that is recommended for the elderly on a long-term basis.
The purpose of this study was to assess the effectiveness of five-toed socks with multiple rubber bits on the foot sole in influencing static postural control among healthy young adults. Twenty six healthy young adults were asked to complete three testing sessions to measure static postural control under three sock conditions: wearing five-toed socks with multiple rubber bits on the foot sole (FS), wearing regular socks (RS), and wearing no socks (NS). For each sock condition, static postural control was assessed on a force plate with the subject in a single-limb stance with eyes open (EO) and eyes closed (EC). The subjects were instructed to stand on the dominant limb as still as possible for 15 seconds. Center of Pressure Velocity (COPV) was calculated in anteroposterior (AP) and mediolateral (ML) directions. The dependent COPV variables were calculated in AP and ML separately for EO and EC trials. The independent variable was sock condition (FS, RS and NS). For each dependent variable, a one-way repeated measures ANOVA was performed, with Sidak post hoc analyses. During EO trials in AP direction, the FS condition (0.53±0.15 cm/second) had a significantly slower COPV value than the RS condition (0.59±0.21 cm/second). During EO trials in ML direction, there was a trend that the FS condition (0.60±0.16 cm/second) had a slower COPV value than the RS (0.67±0.21 cm/second) condition. No significant relationship was observed during EC trials in either AP or ML directions. These results indicate that, during EO trials, the FS condition was associated with increased static postural stability when compared to the RS condition.
The purpose of this study was to determine the effect of cross-country skiing training on dominant leg strength. The study included fifteen junior and twelve youth cross country skiers, and fourteen sedentary male volunteers. Test data were obtained from Cybex II Norm isokinetic strength measurement equipment. Statistical analysis was conducted using the Wilcoxon matched pairs test. Strength was determined at the 60°/sec (Isokinetic Speed 60°/sec Reps 5) and the 180°/sec (Isokinetic Speed 180°/sec Reps 20). Junior cross-country skiers did not have any significant difference for peak torque and ratio between legs (p<0.05). However, youth athletes and the control group had significant side differences in both quadriceps and hamstring muscle strength. Only the junior group did not have any significant ratio difference at 60°/sec, whereas only the control group had a significant ratio difference at 180°/sec between sides (p<0.05). According to the results of this study, there was no significant difference between right and left leg strength of the quadriceps (Q) and hamstrings (H), and Q/H ratios of junior cross country skiers (p<0.05).