Our body has more elements such as joints and muscles than needed to perform any activities of daily living, including gait. As an approach to the problem of motor redundancy, the principle of abundance was suggested. The principle views the apparently redundant design of the body as a useful and crucial mechanism stabilizing different performance variables in a task-specific way. There are many papers based on this idea using the framework of the uncontrolled manifold (UCM) hypothesis. The UCM hypothesis assumes that the central nervous system acts in an abundant space of elemental variables and organizes in that space a subspace corresponding to a stable value of a performance variable. The UCM method has been developed for various actions, including multi-joint reaching, standing, and gait, and used for different subjects (e.g., younger adults, older adults, patients with neurological impairment). Using the method, we explored if segment configurations contributing to the stability of swing foot and center of mass are related to falling risk in older adults. With this paper, we introduce our previous studies as well as the basic concept of motor redundancy and the principle of abundance.

Transcranial alternating current stimulation (tACS) is a noninvasive method of brain stimulation that can modulate oscillatory brain activity in the cortical region. By applying alternating current through two electrodes attached to a subject’s head, it is possible to entrain the oscillation of the cortex directly under one electrode to a specific frequency. In this review, we described our recent findings that tACS to the primary motor cortex and cerebellar hemisphere improves motor performance. We also described the effect of tACS on the supplementary motor cortex to modulate the maintenance and updating of motor plans in a bimanual motor task. These recent findings show that individualized tACS interventions can be tailored by selecting the stimulation area and frequency depending on the subject’s performance level and exercise task. By further investigating the effects of tACS on motor performance, we believe that tACS can be applied to rehabilitation.

The vestibular system and the cerebellum contribute to postural control and ocular movements. Gaze stabilization exercise (GSE) is often conducted to improve postural balance and dynamic gaze ability. We found that GSE reduces body sway while standing upright with modulation of the vestibulospinal reflex. Additionally, the sensory contribution of the vestibular system over postural control increases after GSE. GSE increases the oculomotor range with respect to head movements, thereby improving the dynamic gaze ability. However, this modulation was absent after low-frequency repetitive transcranial magnetic stimulation over the cerebellum (crTMS). These findings indicate that GSE improves eye-head coordination, and the cerebellum contributes to this modulation. Noisy galvanic vestibular stimulation (nGVS) after crTMS modulates vestibulospinal excitability, but no modulation was observed without combining these stimuli. These findings indicate that nGVS can modulate the vestibulospinal reflex, thereby improving postural stability, and the cerebellum contributes to this modulation. The effect of single-pulse cerebellar TMS on spinal reflex excitability can be modulated by cerebellar transcranial direct current stimulation. This indicates that the cerebellum modulates spinal reflexes over postural control, and we can modify this effect by using a neuromodulation montage. In this review, we report the above findings on neuromodulation of the cerebellum and the vestibular system.

Intra-foot kinematics during walking have often been documented using multi-segment foot models. However, the intra-foot kinematics during running remain unclear. Firstly, we investigated changes in kinematic coupling among rearfoot, midfoot, and forefoot during running and walking in normal foot. Strong coupling was observed both tasks between rearfoot eversion/ inversion and midfoot eversion/ inversion, between midfoot eversion/ inversion and forefoot eversion/ inversion. Secondly, we investigated to quantify coordination among rearfoot, midfoot, and forefoot during running in normal foot. Coordination was calculated by using the modified vector coding technique. During the absorption phase, rearfoot–midfoot coordination in the frontal planes was mostly in-phase (rearfoot and midfoot eversion with similar amplitudes). Lastly, we investigated sex differences associated with rearfoot, midfoot, and forefoot kinematics during running. In the rearfoot angle and midfoot angle, females showed a significantly greater range of motion in the sagittal plane as compared with males. Furthermore, anti-phase with proximal dominancy in proportion of frontal rearfoot-shank vs. midfoot-rearfoot couple and midfoot-rearfoot vs. forefoot-midfoot couple in females was significantly increased compared to that in males. In the future, we will verify the intra-foot biomechanics running for patients with flatfoot and pes cavus.

Skeletal muscle oxygen consumption explosively must increase in response to exercise for the generation of adenosine triphosphate. Skeletal muscle arterioles have a crucial role in regulating vascular resistance, contributing to exercise-induced hyperemia. Endothelial cell, which is lining the inner layer of blood vessels, senses and responds to physical stimuli including shear stress and stretch. Muscle stretching is widely performed in patients who undergo physical therapy. Recent clinical studies showed a favorable vascular adaptation after muscle stretching. However, the mechanism underlying stretch-induced vascular adaptation still remains unclear. The aim of this review is to outline the effect of muscle stretching on vascular endothelial function of human. We also aimed to explain the stretch-induced alteration in skeletal muscle microcirculation from mechanistic point of view. Skeletal muscle blood flow acutely decreased by approximately 50% when muscle was stretched. After a 1-month of daily muscle stretching, exercise-induced hyperemia was significantly enhanced in accordance with improvement of endothelium-dependent vasodilation of arterioles, capillarity, and endothelial nitric oxide synthase and vascular endothelial growth factor expression in stretch-treated muscle. In the elderly patients who had limited walking capacity due to symptomatic peripheral artery disease, muscle stretching improved walking distance and augmented flow-mediated dilation of popliteal artery. Therefore, the enhanced arteriolar responsibility, angiogenesis, and increased exercising blood flow could be possible mechanisms underlying stretching-induced improvement of walking capacity.

The central nervous system injury such as stroke can severely cause the motor paralysis. Although the approach of the rehabilitative training is developed, many patients still face the restrictions in their daily living after rehabilitation. Thereby, a new compound with strong potential to enhance motor function recovery with rehabilitation is an unmet medical needs. We focus on the one of glutamate receptors, AMPA (α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid) receptor, which plays an important role in learning and memory. Here, we found a novel small low molecular compound, edonerpic-maleic acid edonerpic MA), facilitated experience-dependent synaptic AMPA receptor delivery in barrel cortex and dramatically accelerated motor function recovery after brain damage in rodent model. Furthermore, edonerpic MA enhanced the upper limb function recovery of macaque monkeys with the internal capsule hemorrhage. Currently, a phase 2 clinical trial is being conducted to verify the efficacy of edonerpic MA in stroke patients and has attracted global attention.

The purpose of this study was to examine the influence of exercise intervention and load difference on age-related lung tissue. Specifically, the morphological changes of the alveolar and the effects of tumor necrosis factor-alpha (TNF-α), interferon-gamma (IFN-γ), and vascular endothelial growth factor (VEGF) on the alveoli were observed. Four months old male Wistar rats were used as the control group (n = 7), the normal rearing group (n = 7) in the following 3 months, the low load exercise group (n = 7), and the high load exercise group (n = 7). The alveolar tissue was visualized using hematoxylin-eosin staining and immunohistochemical staining. Type II epithelial cells were more common in the normal rearing group, and blood cells and pulmonary capillaries were more frequently observed in the high-load exercise group. TNF-α was present in the interstitial tissue while the appearance of alveolar macrophages was negative in the low-load and high-load exercise groups compared to the normal group. On the other hand, VEGF was positive for stromal tissue in the control and high-load exercise group, but negative in the normal rearing and low-load exercise groups. It was suggested that exercise intervention, especially high load exercises, affects epithelial cell distribution and TNF-α and VEGF expression.

Background and aim：In our hospital, we initiated an physical therapy exercise program during dialysis to maintain gait function and exercise tolerance in hemodialysis outpatients. Here, we evaluated the efficacy of this exercise program. Methods：Eight men and women (mean age: 68±8.9 years, range 50-82) functionally independent with regard to gait and activities of daily living engaged in an aerobic exercise program for 30 minutes once daily, 3 times a week for 5 months during dialysis. Before and after each exercise period, the anaerobic threshold value (AT), 6-minute walking distance (6MWD), and 10-m fast walking time (10MFWT) were measured. In addition, knee extension muscle strength (KEMS), 5 times sit to stand test (TST-5), grip strength, fat-free mass index, and body mass index were measured, and self-reported exercise habits were recorded. Results：There were no significant difference in walking function or exercise tolerance before and after implementing the exercise program. In men, the TST-5 became shorter, and the 6MWD became longer after the exercise program. In women, the 10MFWT was significant reduced. KEMS correlated with gait function in all subjects. Conclusion：Aerobic exercise during dialysis maintained walking function and exercise tolerance over 5 months. Daily exercise activities may also maintain leg muscle strength and walking function.

[Purpose] The purpose of this study was to clarify changes in superficial femoral artery blood flow during upper limb cranking exercise. [Methods] Cranking exercise was performed using both upper limbs by 12 healthy adults (age, 20.8 ± 0.4 years). Cardiopulmonary exercise test was performed to determine anaerobic threshold (AT) in advance. After 4 minutes of pre-exercise rest, steady load exercise was performed at the intensity of AT for 9 minutes, followed by 4 minutes of rest after the exercise. Superficial femoral artery blood flow and shear rate were calculated from the blood flow velocity and vessel diameter obtained by using a Doppler imaging system. The heart rate (HR) and cardiac output (CO) were non-invasively measured at rest and during exercise. [Results] Superficial femoral artery blood flow was significantly higher from 6 minutes after the beginning of exercise compared to that obtained at pre-exercise rest (147±8 vs. 226±21 mL/min, 1-min of rest vs. 6-min of exercise, p<0.05). The shear rate was significantly higher from 5 minutes after the beginning of exercise (14±1 vs. 19±1 s\sl185\slmult0 -1, 1-min of rest vs. 5-min of exercise, p<0.05). The HR and CO were significantly higher from 1 minute after the beginning of exercise (HR: 75±2 vs. 98±2 bpm, CO: 5.3±0.3 vs. 7.2±0.4 L/min, 1-min of rest vs. 1-min of exercise, p<0.05, respectively). [Conclusion] In healthy male adults, superficial femoral artery blood flow increased during middle intensity of arm cranking exercise as compared to that obtained at rest. The increase in blood flow was observed after 6 minutes of the beginning of exercise.

The change in the femoral artery blood flow in the non-exercising leg during single-leg pedaling exercise is unclear. Subjects was 12 healthy young adult males (age: 21.2±0.2, height: 173.4±2.0 cm, Weight: 64.3±2.1 kg). We measured the femoral artery blood flow in the non-exercising leg using ultrasound imaging device during single-leg pedaling exercise by a bicycle ergometer. Exercise intensity was set to 50% of Peak V, as determined by cardiopulmonary exercise testing during the one-leg pedaling exercise. Subjects were performed the single-leg exercise for 10 minutes after rest of 4 minutes and warming up of 4 minutes. Superficial femoral artery blood vessel diameter and velocity were measured in the non-exercising leg, to calculate blood flow volume in the superficial femoral artery. The superficial femoral artery blood flow in the non-exercising leg during an exercise was significantly higher than that at rest and prior to the exercise (1min of rest to 10 min of exercise: 197.8±53.2 to 385.2±108.5mL/min, P<0.01). These results suggest that a superficial femoral artery blood flow increases in the non-exercising leg during a single-leg pedaling exercise in healthy adult males.

The movability of ankle joints is a motor function essential to doing lunges, a basic movement in all kinds of sports. In this study, we examined the effect of ankle dorsiflexion angle on the biomechanics of motion during forward lunges.The limbs of 40 healthy participants,80 limbs in total, were examined, and the forward lunge movements were analyzed using a three-dimensional motion analysis unit and floor reaction force gauge. The analysis focused on when the ankle dorsiflexion reached the maximal degree in performing a lunge. In order to clarify the relation between ankle dorsiflexion angle and each of the analytical items, an optimal model was examined using covariance structure analysis.The ankle dorsiflexion angle was significantly related to the forward movement distance of center of foot pressure and the angle of the sagittal floor reaction force.In a forward lunge, the anterior inclination of the lower leg increases when the ankle dorsiflexion angle is wide. Subsequently, it makes it easier for the weight to be vertically loaded on the front leg and thereby the angle of the sagittal floor reaction force becomes more vertical.

Purpose: This study aimed at measuring the knee joint angle on the sagittal plane during walking using two-dimensional motion analysis 2DMA) and three-dimensional motion analysis 3DMA) in patients with stroke, as well as investigate the reliability of both systems, the validity of 2DMA related to criteria, and the similarity of the waveforms for knee kinematic pattern between both systems. Methods: Thirteen patients participated in the study. The knee joint and lower leg rotation angles were measured during walking using 2DMA and 3DMA. The inter-day reliability and validity of the maximum and minimum angles of knee flexion were investigated using the intra-class correlation coefficient and Bland-Altman plots. Also confirmed was the similarity of the waveforms for knee kinematic pattern between both systems. Results: The inter-day reliability was high for both systems. A systematic error was found between 2DMA and 3DMA, whereas a high degree of waveform similarity in the knee joint angle for both systems was observed. Conclusions: The results of this study suggest that 2DMA can be a clinically useful tool for knee kinematic analysis during walking, even in patients with stroke.

The human action of standing up is regarded as a key aspect of maintaining a basic standard of daily life. At clinical sites, a different phenomenon that departs from the standard theory for this action has been observed, suggesting that a distinctive biarticular muscle function is involved. We have previously showed by dynamic electromyographic analysis of the action of moving the trunk to the vertical that the main agonists are the knee joint monoarticular extensor and the rectus femoris. In the present study, we focused on the function of the biarticular muscle acting in a parallel linkage to direct the floor reaction force toward the center of gravity, by constructing a model with the rectus femoris linked in parallel and measuring these changes to clarify the contribution of the rectus femoris to trunk stability during standing up.

The purpose of the present study was to examine the effect of changes in the trunk position on the H-wave and motor evoked potential MEP) of the tibialis posterior TP) muscle in healthy subjects, and clarify the necessity of postural control for the treatment of spastic clubfoot in stroke patients. The participants were 13 healthy people 6 men, mean age 21.6±1.3 years). The following measurements were obtained with the participants in trunk flexion or trunk extension in the sitting position. The electromyography reaction time of ankle dorsiflexion as well as the H-wave and MEP of the TP were measured. The effect of the trunk position on each measured value was determined. When the tibialis anterior TA) muscle was at 5% and 20% of the maximum voluntary contraction MVC), the H wave of the TP was significantly lower in the trunk extended position than in the trunk flexed position. There was no significant difference in the MEP during the different trunk positions at 5% and 20%MVC of the TA. However, under the condition of imaging 20%MVC of the TA, the MEP was significantly higher in the trunk extension position. It was revealed that the spinal reflex of the TP was suppressed by maintaining trunk extension. Moreover, it was suggested that excitability changes in the primary motor cortex of the TP might be involved in this process.

The possibility of estimating muscle passive force from shear modulus using shear wave elastography (SWE) has been reported. However, the relationship between the elastic modulus and the passive force of human skeletal muscles, which is necessary for applications to the human body, has not been elucidated. This study investigates the elastic–passive force relationship in human skeletal muscles at multiple sites. One rectus femoris (RF) muscle was dissected from a Thiel embalmed cadaver. The proximal origin and distal quadriceps tendon were each immobilized with clamps of a pulley device. Calibration weights (0–450 g in 90 g increments) were applied to the distal tendon via a pulley system, and elasticity was simultaneously measured using SWE. The elasticity of the RF was measured at the proximal, central, and distal parts. The results demonstrated that the relationships between the SWE elasticity and the passive muscle force were linear for all the tested sites with coefficients of determination ranging between 0.973 and 0.999. Our study demonstrated that SWE may be used as an indirect method to measure passive muscle force at any site within a muscle in humans.