Anatomical studies reported that human rectus femoris (RF) muscle is comprised of two different muscle-tendon units or neuromuscular compartments. Based on these anatomical characteristics, it can be assumed that the two regions within the RF muscle are controlled via different strategies by the central nervous system and play different functional roles. We are applying multi-channel surface electromyography technique to investigate regionspecific neuromuscular activation within the RF muscle. First, our study demonstrated that the proximal regions selectively activate during hip flexion while whole regions activate during knee extension (Watanabe et al. J Electromyogr Kinesiol 2012, Muscle Nerve 2014). This region-specific functional role was found during walking (Watanabe et al. J Biomech 2014) and pedaling (Watanabe et al. Muscle Nerve 2015). We also reported that regional neuromuscular regulation during walking is influenced by aging (Watanabe et al. J Biomech 2016). These studies suggest that regional neuromuscular regulation plays key role in human movements. Moreover, we showed that proximal regions are more fatigable than other regions (Watanabe et al. Muscle Nerve 2013). This may be explained by the potential of non-uniform arrangements of different types of motor units or muscle fibers along the muscle which was tested by electrical nerve stimulation (Watanabe et al. Eur J Appl Physiol 2014). From these studies, we concluded that the RF muscle is regulated by different strategies during human movements.

The existence of bi-articular muscles greatly contributes to hybrid position and force control, and compliance control of the end point of extremities. In electromyography, the coordinated activity pattern of three pairs of antagonistic muscles, consisting of mono- and bi- articular muscles, contributed to control of the output force direction, and the output distribution at maximum effort was a hexagonal shape with the muscular strength for each pair of antagonistic muscles. In mechanical human leg model experiments, we demonstrated that the parallel link mechanism of a bi- articular muscle along the posterior crus was involved in stabilizing a jumping motion, and that the coordinated contraction mechanism of three pairs of antagonistic muscles in the femoral region contributed to absorbing the force generated during the landing motion. The results obtained from the mechanical leg model experiments strongly suggest that coordinated muscular functions could provide rapid and precise human like movements without a feedback control system.

Injured and dysfunctional tissue often demonstrates abnormal mechanical properties including muscle stiffness. Muscle stiffness can be evaluated via methods such as simple palpation, myotonometry, and standard ultrasonography. Using models based on ultrasound B-mode imaging, changes in the viscoelastic properties of an individual muscle after intervention in clinical practice have been inferred, but more direct quantification of the changes would provide objective insights into these inferences and advance more detailed assessment of rehabilitation efficacy. Recently, developed ultrasound elastography has an advantage in that it is simple to use, virtually real time, mobile, does not require vibrators, and is more affordable. This new ultrasound technology has opened the possibility for objectively quantifying the stiffness of muscle belly in vivo. This technology serves as a foundation for exploring the use of muscle shear modulus as clinically relevant information for assessing the severity of musculoskeletal disorders and potential improvements due to various treatments. In this review, we describe the basic principles of ultrasound elastography techniques and review the current muscle research, including the strengths and limitations of their measurement capabilities.

Human achieves complex and redundant movements, such as standing and walking. Central nervous system (CNS) coordinates huge degree of freedom of the musculoskeletal system. To this end, muscle activities were accounted for with low-dimensional sets of muscle synergies. Present review focused on the muscle synergies to comprehend human movements from the simplification of the redundant degree of freedom. The muscle synergies during human movements were extracted from the data matrix of recorded EMGs of lower limb muscles using non-negative matrix factorization. During postural maintenance in horizontal plane, the CNS flexibly changed patterns of the muscle synergy recruitment to achieve effectively postural control. During gait transition between walking and running, the muscle synergies and their activation profiles dramatically changed when a gait transition was observed. To examine the functional role for existing muscle synergy, learning speed of neural network model with and without muscle synergy layer was calculated. As a result, the learning speed was higher with muscle synergy layer than without it, because the muscle synergy reduces the bias in the mechanical direction of the muscles. From these investigations, present review concluded that complex and redundant human activities are enabled under existence of low-dimensional sets of muscle synergies.

Purpose: We examined the effect of chest wall restriction（ CWR） using an elastic chest band on cardiorespiratory function and autonomic nerve function during steady-state exercise. Methods: Twenty-one healthy subjects performed 9 min of steady-state exercise at a work rate of 80% of ventilatory threshold on a cycle ergometer under CWR and non-CWR. Borg scale ratings of dyspnea, respiratory rate, heart rate, blood pressure, low-frequency （LF） power and highfrequency （HF） power of RR intervals, and the LF/HF ratio were measured during exercise. Blood pressure was measured at rest and at the final 1 min at the end of exercise. Results: Borg scale ratings, the respiratory rate, and heart rate under CWR were significantly higher than those under non-CWR. There was no significant difference in blood pressure at the final 1 min at the end of exercise between CWR and non-CWR. The HF component under CWR was significantly lower than that under non-CWR, whereas the LF/HF ratio under CWR was significantly higher than that under non-CWR. Conclusion: These results indicate that chest pressure fixation by an elastic chest band facilitates sympathetic nerve activity and constricts parasympathetic activity during steady-state exercise.

The purpose of this study was to examine the effect of intermittent heat stress on muscle dysfunction in adjuvant-induced arthritis（AIA） rat. Rats were divided into four groups（n= 6 in each group）: a control（C）, heat stress（C+H）, AIA（A）, and AIA with heat stress（A+H） group. AIA was induced by an injection of complete Freund’s adjuvant to the knee joint cavity. Rats in the C+H and A+H groups were exposed to heated water at 42℃ for 30 min every other day. After 21 days of injection, extensor digitorum longus（EDL） muscles were removed and analyzed for force production and immunobloting. Compared with C group, the maximum specific force was decreased in the EDL muscles from the A and A+H groups. Moreover, the reduction in force production was accompanied by increased expression of TNF-α, 3-nitrotyrosine content, and actin aggregates in these groups. The levels of HSP72 were markedly increased in the C+H and A+H groups. There was no difference in the expression levels of HSP25, αB-crystallin, superoxide dismutase 2, and catalase between the groups. These results suggest that the increased HSP72 expression by intermittent heat stress does not ameliorate muscle dysfunction and inflammatory redox stress in AIA EDL muscles.

Severe cognitive impairment is an established risk factor of falls in the older adults. However, it is unclear whether mild cognitive impairment has an impact for falls and which subtypes of mild cognitive impairment have the greatest association with falls. The purpose of the study was to evaluate the epidemiological evidence linking cognitive impairment and falls. A total of 7712 older adults aged 65 years and older（average age: 73.2 years）participated in the study. Each participant underwent detailed cognitive testing to assess MCI. Screening for MCI included a standardized personal interview, the Mini-Mental State Examination, and the National Center for Geriatrics and Gerontology-Functional Assessment Tool（NCGG-FAT）, which included the tests of memory, attention and executive function, processing speed, and visuospatial skill. The fall rate, single fall during previous year, of cognitively normal, amnestic MCI single domain, amnestic MCI multiple domain, nonamnestic MCI single domain, and non-amnestic MCI multiple domain was 16.7%, 20.1%, 22.6%, 17.5%, and 19.9%, respectively（χ ² = 11.95，p = 0.018）. We found significant relationships between single fall and amnestic MCI multiple domain, the odds ratio was 1.40（95% confidence interval 1.06 to 1.84, p = 0.017）. Future investigation is necessary to determine whether this population is at increased risk for incidence of fall-related disability.

The purpose of this study was to examine the effect of heat stress on diaphragm function in rat with pulmonary hypertension (PH). Male Wistar rats were randomly assigned to control (C), control with heat stress (C+H), monocrotaline-induced PH (M), monocrotalineinduced PH with heat stress (M+H) group. PH was induced in rats by a single injection of monocrotaline (60 mg/kg). C+H and M+H group were exposed to heated water at 42 degree for 30 min every other day for 4 weeks. After 4 weeks of injection, diaphragm muscle was removed and analyzed for force production. To assess mechanisms underlying the effects of heat stress, we measured expression of myofibrillar proteins, heat shock proteins (HSP), antioxidative enzymes, and redox modifications. Compared with C group, there was a decreased tetanic force per cross-sectional area in the M group. The levels of HSP72 were increased in the CH and MH groups, but there was no difference in the expression levels of myosin and troponin T between the groups. The levels of superoxide dismutase (SOD) 2 and catalase were increased in M+H group. The levels of redox modification, including 3-nitrotyrosin, malondialdehyde, S-Nitroso-Cysteine, and methionine sulfoxide, did not differ between the groups. The present study suggests that heat stress can ameliorate PH-induced diaphragm dysfunction. These protective effects could result from increased antioxidative capacities through upregulation of SOD2 and catalase.

The purpose of this study was to determine the relationship between the neuromuscular activation patterns of hip adductor longus (AL), adductor magnus (AM) and hip joint angle during isokinetic hip flexion and extension. For 9 healthy men, surface electromyography was recorded at adductor longus, adductor magnus, rectus femoris, biceps femoris, semitendinosus muscles during isokinetic hip flexion and extension by three different velocities: 60 deg/sec, 90 deg/sec and 120 deg/sec, respectively. The normalized root mean square (RMS) of AL during hip flexion was significantly higher than that of the AL during hip extension. The normalized RMS of AL during hip flexion in 10°to 40°was significantly higher than that in 60° to 70° . The normalized RMS of AM during hip extension was significantly higher than that of the AM during hip flexion. These results suggest that AL is specifically recruited at the hip shallow flexed position of hip flexion and AM is recruited during hip extension.

The purpose of this study was to compare the cerebral blood flow changes during several motor imagery tasks. Nine right-handed healthy volunteers participated in this study. The oxygenated hemoglobin concentrations (oxy-Hb) in the right premotor area (PM), supplementary motor area (SMA), and the primary motor cortex (M1) were measured using a 24-channel near-infrared spectroscopy system in the following 4 conditions: a ball rotation task performed with the subject's left hand (LH), motor imagery induced by watching the video footage of a ball rotation task with otherʼs left hand (MIOLH), a task performed with the subject's right hand (RH), and motor imagery induced by mirror visual feedback of the task performed by the right hand (MIMVFRH). The increase in oxy-Hb over baseline levels during MIMVFRH was larger than that during MIOLH (p < 0.01) and RH (p < 0.05) in the SMA. In the PM and M1, oxy-Hb during LH and MIMVFRH showed no significant changes over baseline values. MIOLH showed no significant changes in oxy-Hb in the motor related areas. We conclude that motor imagery induced by mirror visual feedback increases cerebral blood flow in the SMA and PM, in contrast to a task performed without mirror visual feedback.