More than a hundred years ago, it was first reported that increases in body temperature stimulate minute ventilation. Since then, the characteristics, mechanisms and physiological meaning of this ventilatory response to increasing body temperature, so-called hyperthermia-induced hyperventilation, have gradually been uncovered. For example, it is now known that hyperthermia-induced hyperventilation has a core temperature threshold, like heat-dissipating responses (sweating and cutaneous vasodilation); but several factors affecting heat-dissipating responses do not influence the ventilatory response to increasing body temperature. On the other hand, evidence from several studies suggests there may be some relation between hyperthermia-induced hyperventilation and heat-dissipating responses. In addition, more recent evidence indicates that hyperthermia-induced hyperventilation may be related to central fatigue, which is considered to be one of the reasons exercise performance is diminished in heat. In fact, it has been suggested that hyperthermia-induced hyperventilation causes cerebral blood perfusion to be reduced, which decreases cerebral oxygenation and heat removal. This review presents an overview of the characteristics of the ventilatory response to increasing body temperature and its effect on central fatigue.
A reflex originating in exercising skeletal muscle contributes to sympathoexcitation during exercise. This muscle-based reflex is termed the exercise pressor reflex (EPR). In this review, mechanisms underlying activation of the EPR are examined based on findings mainly obtained from cat studies. Specifically, roles played by chemical and mechanical stimuli due to contraction in increasing discharges of muscle afferent fibers are discussed. Roles metabolic byproducts play in stimulating and sensitizing muscle afferents are also examined. Central cardiovascular sites involved in activation of the EPR are investigated. In this review, moreover, mechanisms by which the EPR function becomes abnormal in heart failure and hypertension are discussed on the basis of experimental data mainly provided by rat studies. In heart failure, the muscle metaboreflex is attenuated while the mechanoreflex is enhanced. In hypertension, both the muscle metabo- and mechano- reflexes are enhanced. Peripheral factors leading to EPR dysfunction in these pathological conditions are examined.
In everyday life, attention is adaptively directed to a stimulus and action in multisensory environments. Recent studies have demonstrated that the functionality of attention and related brain activities are improved by exercise and sports activities. We herein reviewed our previous studies on the neural mechanisms of attention using magnetoencephalography (MEG) and electroencephalography (EEG) (MEEG). MEEG non-invasively records the synchronous activation of neuronal populations from the whole brain of a human as a magnetic field or electric potential with high temporal resolution to the order of milliseconds; and, thus, is a powerful tool for investigating the spatio-temporal dynamics underlying the modulation of real neuronal activities. We presented MEEG data on the neural representations of within-modal, intermodal, cross-modal spatial attention as well as somatic-motor interactions; these were discussed in terms of the effects of attention directed to a stimulus and action on early sensory processing. We also discussed a recent study on attention using a relatively new analysis technique (graph-theoretical or complex network analysis) in human neuroimaging to demonstrate the spatio-temporal dynamics of the functional properties of the human brain network underlying attentional control. These findings support the hypothesis that early sensory processing in modality-specific cortices is regulated, irrespective of the sensory modality, by attentional control signals from the lateral prefrontal cortex, which operates as an important center controlling the flow of information in the human brain.
Skeletal muscle maintains an adequate volume that is commensurate with its surrounding environment. Although intracellular signaling molecules and pathways underlying the regulation of protein synthesis/degradation and subsequent muscle hypertrophy/atrophy are well studied, upstream regulators are largely unknown. In this review, we summarize the recent advances relating to the role of Ca2+ signaling as an upstream regulator of intracellular signaling pathways that regulate muscle plasticity, suggesting a new therapeutic target to control muscle mass.
This review focuses on the suppression of physical performance in a cold environment and the underlying physiological mechanisms. There are many situations where humans have to perform physical activities in a cold environment. Cold environments often limit exercise and working performance by impairing functions such as force production, velocity, power and manual dexterity. A muscle temperature of around 27°C is assumed to be a critical temperature below which maximal voluntary isometric force starts to decrease. The endurance time of submaximal isometric contractions peak at muscle temperatures of 27 to 28°C and decrease rapidly above and below these temperatures. Dynamic exercise performance, especially fast velocity movement, is generally more disturbed by cooling than isometric contractions. Additionally, the effect of cold adaptation on exercise performance, and the potential related mechanisms are summarized here based on a limited number of studies. Since the involuntary muscle contraction of shivering disturbs fine motor control, habituation of shivering, which is an example of cold adaptation, potentially improves exercise performance. Higher hand skin temperatures, induced by greater cold induced vasodilatation after local cold adaptation, could improve manual dexterity. Since there have been few studies testing the effect of cold adaptation on exercise performance in a cold environment, further studies seem warranted.
This review summarizes recent findings regarding the status of physical activity and introduces effective methods of intervention. Data from our serial cross-sectional study between 2003 and 2012 suggested that the decline in step counts over the last decade is mainly related to a reduction in non-exercise activity associated with the increased use of cell phones or computers and with playing video games. We then examined the effects of lifestyle interventions using an activity monitor with computerized game functions or an activity monitor and Twitter on physical activity and body composition. These findings suggested that lifestyle interventions using both of these strategies increases daily physical activity and reduces body fat more effectively than using an activity monitor alone. In addition, changes in physical activity and in body fat were significantly correlated. We also applied a randomized intervention to examine an effective method of increasing physical activity levels among college physical education students using a pedometer. We found that using a pedometer and inducing friendly competition or encouragement from peers increased step counts more effectively during soccer classes. These findings therefore have important implications for ensuring compliance with the Physical Activity Reference for Health Promotion 2013 and Active Guide.
Neural output from the locomotor system for each arm and leg influences the spinal motoneuronal pools directly and indirectly through interneuronal (IN) reflex networks. This review article mainly describes the recent findings concerning the existence, features and functions of common IN systems on spinal reflex pathways induced by multisensory inputs during human locomotion. In particular, we focus on regulation of polysynaptic cutaneous reflex pathways assessed by spatial facilitation. Furthermore, we provide evidence for activation of common presynaptic inhibitory INs that integrate locomotor-related commands and antagonist group Ia inputs. The experimental results are discussed in light of recent advances in motor control in humans and other animals with implications for locomotor rehabilitation.
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.
Concurrent training, which is a combination of resistance exercise (RE) and endurance exercise (EE) performed in succession, is used to improve both muscle strength and cardiovascular function. Although numerous studies have investigated the effects of concurrent training on muscle adaptation, no consensus has been reached. Skeletal muscle adaptation is induced by the cumulative effects of the repeated cellular and molecular responses to an acute bout of exercise. Divergent exercise modes induce different molecular signaling responses depending on the muscle contraction type. It is well known that RE induces the mammalian target of the rapamycin complex 1 (mTORC1) signaling pathway while EE activates AMP-activated protein kinase (AMPK) signaling, and the signaling pathways stimulated by each exercise could interfere with each other. Thus, the inconsistencies in the effects of concurrent training on muscle adaptation may be explained by the different signaling interactions occurring in response to RE and EE. This review article describes the signaling pathways induced by RE, EE, and concurrent training.
In this study, we investigated the retention of technetium-99m sestamibi (MIBI), a radiopharmaceutical that accumulates in mitochondria, in patients with type 2 diabetes. We hypothesized that patients with type 2 diabetes had lower MIBI counts in their legs than non-diabetic volunteers, and that these abnormalities reflected a low anaerobic threshold (AT) during cardiopulmonary exercise testing (CPX). Eight non-diabetic volunteers (Group N) and 11 patients with type 2 diabetes (Group D) underwent CPX. Mitochondrial function was assessed using MIBI imaging of both legs. The MIBI counts in the legs were significantly lower in Group D than in Group N (D vs. N: 74.1 vs. 94.1 counts/pixel, p < 0.05). Similarly, peak oxygen uptake (peakVO2) and AT were lower in Group D than in Group N (peakVO2: 19.8 vs. 26.5 ml/kg/min, p < 0.05; AT: 13.1 vs. 17.2 ml/kg/min, p < 0.05). A strong correlation was observed between MIBI counts and the peakVO2 and AT (peakVO2: r = 0.62, p < 0.01; AT: r = 0.76, p < 0.01). After the exclusion of an outlying subject, the correlation between peakVO2 and MIBI count in the legs was lost (r = 0.28, p = 0.26); however, the AT correlation was maintained (r = 0.59, p = 0.01). Patients with type 2 diabetes had reduced skeletal muscle MIBI counts, indicating reduced mitochondrial function. This abnormality may be linked to a low AT.
Heat shock protein 25 (Hsp25) phosphorylation plays a protective role following mechanical stress in skeletal muscle fibers. We previously reported that phosphorylation at serine 15 of Hsp25 (p-Ser15) was enhanced during regrowth of muscle fibers in rats with muscle atrophy due to tail suspension. However, it is still unclear how p-Ser15 contributes to myogenesis and regeneration of skeletal muscle fibers. We performed the present study to investigate p-Ser15 levels at different stages of myogenic differentiation in regenerating soleus muscle fibers of adult rats. Muscle regeneration was induced by muscle injury with intramuscular injection of cardiotoxin into the soleus. On day 14 after injury, p-Ser15-positive cells were noted in the regenerating soleus. The nuclei in small p-Ser15-positive cells contained myogenin, but not Pax7. Most of these cells did not exhibit peripheral localization of dystrophin, indicating that these cells were myotubes or immature fibers. Desmin and actinin were present in all cells and fibers regardless of p-Ser15 expression. Forced contraction by nerve stimulation led to increased phosphorylation at Ser15 in the regenerating soleus, as determined by western blot. Furthermore, elevated p-Ser15 was noted particularly in small cells with cross sectional areas less than 300 µm2. These results suggest that small immature fibers are responsive to muscle contraction, and subsequently induce a protective response through the phosphorylation of Hsp25.
In mountain climbing, short pre-exposure to hypoxia at the midway point of a high mountain is often carried out before heading to a higher altitude. However, the effects of such exposure have not been examined experimentally. This study aimed at investigating the effects of short pre-exposure to hypoxia on physiological responses to subsequent hypoxic exercise. Thirteen male sea-level residents participated in 2 tests. Both tests consisted of 60-min normobaric exposure followed by 15-min stepwise incremental ergocycle exercise (five workloads) under hypoxic conditions (fractional inspired oxygen concentration [FiO2] = 0.167). Conditions during normobaric exposure were hypoxic (FiO2 = 0.167) or normoxic (FiO2 = 0.209). Results of the two-way analysis of variance (oxygen concentration × exercise intensity) showed significant oxygen concentration effects on heart rate (HR), carbon dioxide production (VCO2), and rating of perceived exertion during hypoxic exercise. Significant interaction effects were found in minute ventilation and VCO2. Post hoc tests compared these parameters after hypoxic exposure with those after normoxic exposure at each workload, and only showed a significant difference in HR at workload 2. A significant negative correlation was observed between peak oxygen uptake (VO2) measured in normoxia and ratio of arterial oxygen saturation (SpO2) after hypoxic exposure to that after normoxic exposure at workload 5. The present study could not clearly show through post hoc tests the significant effects of short hypoxic pre-exposure on physiological responses to subsequent hypoxic exercise, while it indicated that those with relatively higher peak VO2 showed a greater decrease in SpO2 during hypoxic exercise after hypoxic exposure than after normoxic exposure.
In the present study, a tandem-bicycle ergometer was developed, because it is believed that such an ergometer can be used to eliminate differences in signaling between single- and tandem-exercise in cardiorespiratory responses, and is able to quantify interdependence in one load. It is necessary to verify whether cardiorespiratory responses to submaximal exercise are the same between single and tandem-bicycle ergometers. Accordingly, we compared cardiorespiratory variables during exercise in three conditions: 1) with a general bicycle single saddle using a general bicycle ergometer, 2) with a tandem bicycle front saddle using a tandem ergometer, and 3) with a tandem bicycle rear saddle using a tandem ergometer. Eleven healthy males participated in this study. The subjects exercised for 15 min at three intensities (1.5, 2.0 and 2.5 kp) in each condition. The pedaling rate was constantly kept at 60 rpm. Heart rate (HR), oxygen uptake (VO2), and the rating of perceived exertion (RPE) were measured during the last minute of each intensity. There were no significant differences in the variables HR, VO2, and RPE at each load among the three conditions. The ranges of coefficient of variation (CV) values were 3.0 - 4.8%: HR and 4.2 - 5.1%: VO2. It was reported that between-day CV for HR and VO2 during treadmill running was 1.0 - 10.7% and 1.9 - 11.6%. Given these CV values of present and previous studies, it can be seen that physiological response is stable during developed tandem-bicycle ergometer exercise. These results suggest that cardiorespiratory responses to exercise are at comparable levels between a normal bicycle ergometer and the newly developed tandem-bicycle ergometer.