Human movement is a consequence of joint torque or muscle force produced by muscle or muscle groups. Therefore, motor performance in human movements can be determined by the accuracy of joint torque or force produced by muscle/muscle groups. Since motor unit (MU) activity contributes to the force exerted by muscle, the ability to accurately perform steady contractions should be attributed to MU discharge patterns and MU contractile properties. Force fluctuations, which reflect accuracy in fine motor output, can thus affect an individual’s motor control abilities, for example, using chopsticks or going for a walk. Accordingly, mechanistic investigations into the characterization of force fluctuations will provide valuable information concerning the modalities needed to improve or regain motor control in healthy and clinical populations. This paper describes the physiological mechanisms responsible for the adaptation of force fluctuations to various environments. Methodologies for analyzing force fluctuations, particularly in multiple muscle systems, are also addressed to provide additional insights into the mechanisms of fine motor control.
There has been a growing interest in dog ownership and walking as a unique and potential resource to provide physical activity for many individuals in the community. The present study reviewed current trends regarding the studies on dog ownership, dog walking, and human health, and clarified the future direction of research on the topic. There is evidence to suggest that it is not dog ownership itself, but rather dog-walking that contributes to increased physical activity and the likelihood of meeting public health guidelines for physical activity. Also, a growing body of literature indicates that dogs appear to provide an important form of social support, motivation, and obligation that encourages dog owners to walk. Regarding the environmental and policy-related factors associated with dog walking, some literature showed that access to a dog-supportive park/area or living in a walkable neighborhood seems to positively affect dog owners walking with their dog. The evidence is still limited on interventions for promoting dog owners walking with their dog. With the high level of dog ownership in many industrialized countries, further evaluation of physical activity, including dog walking and use of an accelerometer, identification of factors related to dog owners’ regular/irregular dog walking by means of a longitudinal study, and implementation of an intervention study related to the promotion of physical activity among dog owners with a focus on dog walking are needed.
In primates, unilateral voluntary movements are preferentially controlled by the primary motor cortex (M1) contralateral to the side performing the movement. However, it has been reported that the M1 ipsilateral to the side performing the movement (ipsi-M1) is also activated during unilateral voluntary movements. Recently, studies involving transcranial magnetic stimulation (TMS) or functional magnetic resonance imaging (fMRI) techniques have gradually elucidated the neural mechanisms responsible for modulating ipsi-M1 activity. In particular, the modulation of ipsi-M1 activity is likely to occur in a task-dependent manner, and is also closely associated with advancing age. In addition, ipsi-M1 excitability is suppressed during the acquisition phase of motor learning. Previous studies have suggested that the modulation of ipsi-M1 activity occurs via changes in the activation of the corpus callosum pathways linking the bilateral M1. In this article, we will broadly review the features of ipsi-M1 activity, observed during the execution of unilateral movements, as well as the detailed neural mechanisms underlying the modulation of ipsi-M1 activity. Understanding the role played by ipsi-M1 activity during voluntary movements would improve our knowledge of human motor control systems.
This review introduces a variety of human circadian rhythms including physiological processes and mental and physical performances, with reference to real-life situations. Circadian rhythms play a role in physiological processes, such as core body temperature and plasma melatonin, which are recognized as the body clock. As humans are diurnal organisms, mental performance declines primarily at night, secondarily in the early afternoon; this is consistent with risks of traffic and industrial accidents. Physical performance is composed of various fitness components and generally reaches its peak and nadir at around evening and early morning, respectively. Exceptions to this are body balance control and accuracy, both of which require brain function. Although maximal oxygen consumption (VO2 max) measured in the laboratory shows a constant value independent of the time of day, actual endurance capacity might be determined by core body temperature at the beginning of exercise, thermoregulatory response, and environmental temperature and humidity, all of which vary with the time of day. As the most powerful factor affecting the human circadian clock is bright light, physical exercise may be one factor entraining the human circadian pacemaker. However, experimental evidence has suggested that exercise itself has little or no influence on shifting the human master clock. Although further studies are required, recent studies have demonstrated that physical exercise at a certain time of day specifically improves physical performance at the same time, which might be independent of the master clock.
Neurogenic hypertension, the primary form of essential hypertension, is one of the most common diseases worldwide. Hypertension is a risk factor for many cardiovascular diseases such as heart attacks and stroke; therefore, it is crucial to maintain arterial blood pressure (BP) within the normal range. Regular aerobic exercise at moderate intensities can lower basal BP, and is a recommended therapy to prevent or improve primary hypertension. However, the mechanisms underlying the anti-hypertensive effects of exercise remain unknown. In this review, we discuss the mechanisms for the anti-hypertensive effects of exercise training/therapy that are hypothesised from recent findings, including our own. In particular, we discuss the nucleus of the solitary tract (NTS) of the brainstem, which is involved in mechanisms underlying the manifestation of neurogenic hypertension. Moreover, the NTS may also be involved in the anti-hypertensive effects of exercise training. However, exercise training does not seem to improve causative genetic factors for neurogenic hypertension in the NTS. Nevertheless, exercise training may affect other mechanisms responsible for neuroactive ligand-receptor interactions within the NTS, which also regulate BP homeostasis. We hope this review will further enhance research in this and promote exercise habits that help delay or even prevent the progression of essential hypertension.
Cortical bone is porous in infants but compacts with growth. In that process, circumferential lamellae are formed on the endosteum (inner) side of cortical bone first, and also the periosteum (exterior) side, after that. A mature rat shows higher bone strength per unit area of the cortical bone, and this means that not only an increase in the bone mass, but also improvement of the bone structure contributes to enhancing the bone strength. External morphology of the bone hardly changes by immobilization, but the thickness of the cortical bone decreases, and disorder of the running direction of the blood vessels in the cortical bone also occurs. Bone formation and resorption are caused simultaneously at the early stage of an exercise period, and it is supposed that factors embedded in the bone matrix beforehand are released into bone marrow by exercise, differentiating and activating the osteoblasts. Thus, it is thought that bone adapted to mechanical stress is formed by repeating active remodeling in the growing period.
Today, a large proportion of persons with spinal cord injury (SCI) can return to society thanks to advances in biomedical care. Various sports activities are recommended, especially for wheelchair-bound disabled persons with SCI, in order to maintain proper physical fitness. It is important to know sports activities-induced physiological specificity in persons with SCI before recommending sports activities. Natural killer cell activity (NKCA) is commonly used to study immune response during exercise. Interleukin (IL)-6 is produced by contracting skeletal muscles and then released into the circulation; and is considered to mediate the health benefits of exercise against chronic diseases. We investigated the responses of NKCA and IL-6 in SCI persons during arm exercise and a wheelchair marathon race. Similar NKCA and IL-6 responses were found in thoracolumbar SCI persons and able-bodied (AB) persons. On the other hand, changes in NKCA and IL-6 in cervical SCI persons elicited different characteristic patterns compared to thoracolumbar SCI and AB persons.
Wingless-related MMTV integration site (Wnt) family members are secreted glycoproteins with a molecular weight of approximately 40kDa, and are categorized as cytokines involved in various phases of life phenomena, such as ontogenesis, morphogenesis, and carcinogenesis. The glycoproteins are conserved in various species from C. (Caenorhabditis) elegans to mammals, and 19 types of Wnt homologs have been identified in humans. The Wnt signaling pathway is broadly classified as either a canonical or noncanonical pathway. The Wnt canonical signaling pathway stimulates bone formation, and this pathway is inhibited by Sclerostin, which is known to be produced by osteocytes and to inhibit bone formation. Because mechanical loading is reported to inhibit the production of Sclerostin in osteocytes and to enhance bone formation, osteocytes are recognized as mechanosensors in the hard tissue. Recently, clinical administration of anti-Sclerostin antibody was begun for osteoporosis. Here we outline the roles of Wnt signaling in bone formation and describe the current status of use of anti-Sclerostin antibody.
The occurrence of sarcopenia and muscular dystrophy with aging has attracted attention. Many factors are reported as causes of sarcopenia, such as the functional decline of a digestive organ occurring with aging and malnutrition due to a decrease in food intake. Also, a decrease in growth hormone and an increase in cytokines are also considered to be causes of sarcopenia. Meanwhile, the differentiation between sarcopenia and disuse muscle atrophy is not clear. It will be important in future studies to clearly define the differences between sarcopenia and disuse muscle atrophy. Recently, the diagnostic criteria of sarcopenia have been defined according to a large-scale investigation. In the future, an easier sarcopenia diagnostic method should be developed. It is necessary to design specific treatment strategies more closely correlated to the clinical condition of individual patients, because the causes of sarcopenia vary widely. In this review, we summarize the characteristics of the clinical condition, diagnosis, and treatment of sarcopenia.
The effects of the intermittent incorporation of high-intensity downhill running sessions into long-term endurance training were assessed by examination of the plantaris muscle of rats. First, the intrinsic effects of a single session were evaluated in otherwise sedentary rats. The experimental group showed histological injuries in 2–3 days after the session. In addition, compared with the sedentary control, the experimental group showed a sevenfold increase in the fraction of type IIc fibers, and deceases of 74 and 88% in tetanic force evoked indirectly and directly, respectively, by electric stimulation. The injured muscle fibers showed regeneration within 21 days as evidenced by centrally located nuclei. Next, the effects of intermittently incorporated downhill-running sessions into a 9-week endurance training regimen were tested using two experimental groups: Training and Training + Downhill. On the first day of the 1st, 3rd, 5th, and 7th weeks of the training period, the rats in the Training + Downhill group experienced downhill-running sessions. After the endurance training period, the plantaris muscle of the two experimental groups demonstrated higher fatigue resistance with an increase in the type IIa fiber fraction, at an expense of the type IIb fiber fraction. Compared with the Training group, the Training + Downhill group had a higher type IIa fiber fraction, with clusters of 70–100 type IIa fibers. These results indicate that intermittent high-intensity sessions promote the fiber type transition induced by daily endurance training. However, the potentially adverse effect of fiber type cluster formation suggests that there is an optimum intensity and frequency of the high-intensity exercise sessions for better enhancing the effects of long-term endurance training.