Bending Angle Sensor Based on Double-Layer Capacitance Suitable for Human Joint.

Goal: To develop bending angle sensors based on double-layer capacitance for monitoring joint angles during cycling exercises. Methods: We develop a bending angle sensor based on double-layer capacitive and conducted three stretching, bending, and cycling tests to evaluate its validity. Results: We demonstrate that the bending angle sensor based on double-layer capacitance minimizes the change in the capacitance difference in the stretching test. The hysteresis and root mean square error (RMSE) compared with the optical motion capture show hysteresis: 8.0% RMSE and 3.1° in the bending test. Moreover, a cycling experiment for human joint angle measurements confirm the changes in accuracy. The RMSEs ranged from 4.7° to 7.0°, even when a human wears leggings fixed with the developed bending-angle sensor in the cycling test. Conclusion: The developed bending angle sensor provides a practical application of the quantitative and observational evaluation tool for knee joint angles.

Postural sway reduction by weak electrical noise into the wrist median nerve using portable stimulator.

Stochastic resonance (SR) is a weak noise stimulation that improves the function of standing balance by increasing sensitivity to somatosensory information. SR implemented in the lower limbs may increase the standing balance function, but the effect of noise stimulation on upper limbs has not been investigated to date. This study aims to investigate the effect of weak electrical noise stimulation of the median nerve at the wrist on the balance control system function using a portable stimulator. Ten healthy individuals participated in the study. Each subject maintained quiet standing with their eyes closed for 40 s while receiving white noise electrical stimulation to the median nerve at the wrist. Center of pressure (COP) displacement and change in the joint position (left and right waist) were measured and compared between a no-stimulus trial (control trial) and a stimulus intensity trial that maximized the effect of SR (optimal trial). Experimental results show that weak electrical noise stimulation of the median nerve at the wrist stabilized the COP and joint position. The anteroposterior (AP) standard deviation of the optimal trial were significantly reduced compared to the control trial in terms of COP and left and right waist, and AP low-frequency range power of the optimal trial were significantly reduced compared to the control trial in terms of COP and left waist. AP mean velocity and AP high-frequency range power at the left waist were significantly reduced in the optimal trial. It was concluded that weak electrical noise stimulation applied to the median nerve can reduce static postural sway.

Effects of subthreshold electrical stimulation with white noise, pink noise, and chaotic signals on postural control during quiet standing.

BACKGROUND: The stochastic resonance (SR) phenomenon has been used to improve postural control through the application of imperceptible noise to the somatosensory system. White noise signals have been applied in numerous SR studies on postural control. However, because the SR effect depends on the noise structure, the stimulation effects of signals with different structures, such as pink noise and chaotic signals, on postural control, must be determined to achieve better clinical applications of SR technology. RESEARCH QUESTION: During quiet standing, how is postural control affected by subthreshold electrical stimulation to the knee joints when signals with different structures (white noise, pink noise, and chaotic signals) are used? METHODS: Sixteen healthy young adults stood quietly for 40 s with their eyes closed. To evaluate postural sway, we calculated the mean velocity, root mean square (CoPRMS), and range (CoPRange) values for the center of pressure (CoP) in the anteroposterior direction. The standing task was conducted under subthreshold electrical stimulation with white noise, pink noise, and chaotic signals based on the Lorenz system, in addition to the no-stimulation condition. The four stimulation conditions were randomized within each set and repeated seven times. RESULTS: Significant effects of stimulation were observed in the CoPRMS and CoPRange values. The CoPRMS value under the pink noise signal was significantly lower than that under the no-stimulation condition. The CoPRange value also tended to decrease under the pink noise signal compared with the no-stimulation condition; however, the differences were not statistically significant. No significant changes were found with the white noise and chaotic signals compared with the no-stimulation condition. SIGNIFICANCE: We demonstrated that the pink noise signal was more effective in reducing postural sway than the white noise and chaotic signals based on the Lorenz system during quiet standing.

Movement Coordination during Forward and Backward Rope Jumping: A Relative Phase Study.

Rope jumping is a popular training method in athletic programs, fitness, and physical education. Forward and backward rope jumping has been used for evaluating athlete's performance. Both of these two jumps require coordination in the upper and lower limbs. However, no study has focused on movement coordination during forward and backward rope jumping. Relative phase (RP) analysis was widely known as an innovative method for evaluating human movement coordination. Thus we aimed to investigate the movement coordination during forward and backward rope jumping by using RP analysis. 78 elementary and junior high school students participated in this study. 30 seconds rope jumping was recorded for both forward and backward by using iPhone video. Pose estimation software was used for jump motion tacking. Movement coordination was analyzed through RP analysis, absolute maximum value, mean absolute RP, and deviation phase were calculated for evaluating movement coordination, the trend of in or out-of-phase, as well as movement stability. As a result, 3994 forward and 3961 backward jumps were analyzed. There was a significant difference in movement coordination between forward and backward rope jumping. Compared to forward, backward jumps showed worse movement coordination, a trend to be out-of-phase, and less stability. It was the first time that movement coordination during rope jumping was studied. We considered that further research on coordination during rope jumping can provide new insight into athlete performance management, fitness guidance, and physical education.

Design and Evaluation of an Online Squat Fitness System: Lessons Learned During the Early COVID-19 Pandemic in Japan.

COVID-19 has changed our lives and limited our ability to have adequate physical activity (PA). It is necessary to replace outdoor PA with home-based fitness. However, people lack access, skills, and even motivation for home-based fitness. To address these issues, we designed a free access self-monitoring and coaching and music-based interactive online squat fitness system. Body weight squat was utilized for fitness exercise and evaluated based on three indices: knee width, hip depth, and rhythm. An online survey on changes in exercise due to the COVID-19 pandemic and exercise habits was conducted to investigate the effect of the COVID-19 pandemic on PA. We collected data from 557 respondents 5 months after the system first released and analyzed 200 visitors' performance on squat exercise and the other relevant parameters. Visitors were divided into three groups according to their age: younger, middle, and older groups. Results showed that the younger group had better squat performance than the middle and older groups in terms of hip depth and rhythm. We highlighted the lessons learned about the system design, fitness performance evaluation, and social aspects, for future study of the design and development of similar home-based fitness systems. We provided first-hand results on the relation between the COVID-19 pandemic and physical exercise among different age groups in Japan, which was valuable for policy making in the post-COVID-19 era.

Cross-correlated fractal components of H-wave amplitude fluctuations in medial gastrocnemius and soleus muscles.

The time series of the H-wave amplitude in soleus muscle (SOL) shows fractal (long-range) correlation, which is attributed to input from supraspinal centers. However, whether such long-range power-law correlated input also contributes to the synergistic muscles remains unclear. The purpose of this study was therefore to examine the correlation in the fractal components of H-wave amplitude fluctuations between the synergistic muscles used for plantar flexion, i.e., the medial head of the gastrocnemius muscle (MG) and SOL. In eight young male participants, consecutive H-reflexes were recorded almost simultaneously from the MG and SOL at a stimulation frequency of 0.5 Hz for 30 min. We performed detrending moving-average cross-correlation analysis (DMCA) for each of the H- and M-wave amplitude time series between MG and SOL to assess the existence of a common noise input contributing to these long-range correlations. The cross-correlation coefficient ρDMCA (-1 to 1) was calculated to quantify the strength of the correlation between two different time series. The results indicated a significant long-range power-law correlation between H-wave amplitudes in MG and SOL (ρDMCA: 0.50 (0.22) and 0.22 (0.17), mean (standard deviation) for the original and randomly shuffled surrogate data, respectively, P < 0.05). This was not the case for M-wave amplitudes (ρDMCA: 0.29 (0.23) and 0.20 (0.15), P > 0.05). We conclude that there is a common noise input governing these synergistic muscles, possibly due to supraspinal origin, causing long-range power-law correlations in monosynaptic reflexes.

Attenuated spontaneous postural sway enhances diastolic blood pressure during quiet standing.

PURPOSE: Spontaneous postural sway during quiet standing has been considered a simple output error of postural control. However, as postural sway and inherent body orientation evoke compensatory activity of the plantar flexors, they might contribute to blood circulation under gravitational stress via the muscle pump. Hence, the present study employed an external support device to attenuate the plantar flexor activity in supported standing (SS), to experimentally identify its physiological impact on blood circulation. METHODS: Eight healthy young subjects performed two 5-min quiet standing trials (i.e., normal standing (NS) and SS), and the beat-to-beat interval (RRI) and blood pressure (BP) were compared between trials. We confirmed that postural sway and corresponding plantar flexor activity, quantified by the anteroposterior displacement of the foot center of pressure and lower back position with respect to the wall, and by the amplitude of electromyography and mechanomyography, respectively, were attenuated in SS, while mean body orientation angle and relative position of the BP sensor were comparable to NS. RESULTS: The 5-min averages of diastolic BP and mean arterial pressure during SS were significantly higher than during NS, while RRI and systolic BP did not change. These could be interpreted as an increase in peripheral vascular resistance; meanwhile, in NS, this effect was replaced by the muscle pump of the plantar flexors. CONCLUSION: The muscle contractions related to spontaneous postural sway and body orientation produce substantial physiological impact on blood circulation during quiet standing.

The Estimation of Circadian Rhythm Using Smart Wear.

In this study, we have developed a new practical system for estimating circadian rhythm by using smart wear that can measure electrocardiogram (ECG) during sleep. This system can estimate the time and heart rate (HR) value to reach the lowest point in circadian rhythm. We show the system in detail. And for further application, we conducted the experiment for showing the effects of jet lag on the circadian rhythm by using the developed system. The results showed that the time of the lowest HR shifted earlier and the lowest HR was higher in case of traveling in a westward direction.

Development of wearable muscle fatigue detection system using capacitance coupling electrodes.

Bio-information is important to confirm the body condition. Especially, the muscle fatigue is related to injury or decrease of concentration. Therefore, it is required to evaluate muscle fatigue to make subject enjoy sports. In previous study, muscle fatigue is evaluated by using electromyogram (EMG). However, the electrode for EMG measurement is generally used for contact manor. The electrodes are disposable and it might cause the irritation of skin. Therefore, it isn't fitted for measurement of muscle fatigue. We developed wearable muscle fatigue detection system using capacitance coupling electrodes. Developed system isn't caused the irritation by electrodes and can reuse it. We compared the conventional system using disposable electrode system and our system to evaluate performance. We evaluated muscle fatigue from electromyogram before and after futsal. An integrated electromyogram and an intermediate frequency were used for the evaluation of muscle fatigue. As a result, half of subjects showed tendency of muscle fatigue. Therefore, we showed the possibility as muscle fatigue detection system using the capacity coupling electrodes.

Panaxatriol derived from ginseng augments resistance exercised-induced protein synthesis via mTORC1 signaling in rat skeletal muscle.

Resistance exercise activates muscle protein synthesis via the mammalian target of rapamycin complex 1 (mTORC1) pathway and subsequent muscle hypertrophy. Upstream components of the mTORC1 pathway are widely known to be involved in Akt and extracellular signal-regulated kinase 1/2 (ERK1/2) signaling. Previous studies have shown that ginseng stimulated Akt and ERK1/2 signaling. Therefore, we hypothesized that panaxatriol (PT) derived from ginseng triggers mTORC1 signaling and muscle protein synthesis by activating both the Akt and ERK1/2 signaling pathways, and that PT additively stimulates muscle protein synthesis when combined with resistance exercise. The study included male Sprague-Dawley rats. The legs of the rats were divided into control, PT-only, exercise-only, and exercise + PT groups. The right legs were subjected to isometric resistance exercise using percutaneous electrical stimulation, whereas the left legs were used as controls. PT (0.2 g/kg) was administered immediately after exercise. The Akt and ERK1/2 phosphorylation levels were significantly higher in the exercise + PT group than in the exercise-only group 0.5 hour after exercise. The phosphorylation of p70S6K was significantly increased at both 0.5 and 3 hours after exercise, and it was higher in the exercise + PT group than in the exercise-only group at both 0.5 and 3 hours after exercise. Muscle protein synthesis was significantly increased 3 hours after exercise, and it was higher in the exercise + PT group than in the exercise-only group 3 hours after exercise. Our results suggest that PT derived from ginseng enhances resistance exercise-induced protein synthesis via mTORC1 signaling in rat skeletal muscle.

Acute bout of resistance exercise increases vitamin D receptor protein expression in rat skeletal muscle.

NEW FINDINGS: What is the central question of this study? Does an acute bout of exercise alter vitamin D receptor expression in rat skeletal muscle? What is the main finding and its importance? Resistance exercise but not endurance exercise increased intramuscular vitamin D receptor expression. Thus, resistance exercise may be an effective way to increase muscle vitamin D receptor expression. Vitamin D and vitamin D receptor (VDR) are involved in the maintenance of skeletal muscle mass and function. Although resistance exercise is well known to enhance muscle growth and improve muscle function, the effect of resistance exercise on VDR has been unclear. We investigated intramuscular VDR expression in response to an acute bout of resistance exercise or endurance exercise. Male adult Sprague-Dawley rats were subjected to either resistance exercise (isometrically exercised via percutaneous electrical stimulation for five sets of ten 3 s contractions, with a 7 s interval between contractions and 3 min rest intervals between sets) or endurance exercise (treadmill at 25 m min(-1) for 60 min). Rats were killed immediately or 1, 3, 6 or 24 h after completion of the resistance or endurance exercise, and gastrocnemius muscles were removed. Non-exercised control animals were killed in a basal state (control group). Intramuscular VDR expression was significantly higher immediately after resistance exercise and elevated for 3 h after exercise compared with the control group (P < 0.05), and the resistance exercise significantly increased phosphorylated ERK1/2 and Mnk1 expression (P < 0.05), which may be associated with VDR expression, immediately after exercise. Additionally, intramuscular expression of cytochrome P450 27B1, an enzyme related to vitamin D metabolism, was significantly higher at 1 and 3 h after exercise (P < 0.05) compared with the control group. In contrast, endurance exercise had no effect on any of the measured proteins. Our results indicate that resistance exercise may be an efficient way to increase intramuscular VDR and related enzyme expression.

Reentrant excitation in an analog-digital hybrid circuit model of cardiac tissue.

We propose an analog-digital hybrid circuit model of one-dimensional cardiac tissue with hardware implementation that allows us to perform real-time simulations of spatially conducting cardiac action potentials. Each active nodal compartment of the tissue model is designed using analog circuits and a dsPIC microcontroller, by which the time-dependent and time-independent nonlinear current-voltage relationships of six types of ion channel currents employed in the Luo-Rudy phase I (LR-I) model for a single mammalian cardiac ventricular cell can be reproduced quantitatively. Here, we perform real-time simulations of reentrant excitation conduction in a ring-shaped tissue model that includes eighty nodal compartments. In particular, we show that the hybrid tissue model can exhibit real-time dynamics for initiation of reentries induced by uni-directional block, as well as those for phase resetting that leads to annihilation of the reentry in response to impulsive current stimulations at appropriate nodes and timings. The dynamics of the hybrid model are comparable to those of a spatially distributed tissue model with LR-I compartments. Thus, it is conceivable that the hybrid model might be a useful tool for large scale simulations of cardiac tissue dynamics, as an alternative to numerical simulations, leading toward further understanding of the reentrant mechanisms.

Hyperthermia system with thermoseed set in abdominal cavity and AC-magnetic-field.

We propose a hyperthermia system for cancer developed in abdominal cavity. Local/deep spot heating and its less invasion feature are expected to be realized by thermoseed. This thermoseed is made of ferromagnetic material and it changes AC magnetic field power from outside of body to heat. AC magnetic field frequency is set on the value not to be absorbed to organs or tissues. We made a heat model of thermoseed and in vivo environment. The amount of heat and heat conduction were calculated from the characteristic values of materials and AC magnetic field. Effective shape of thermoseed for hyperthermia can be designed easily from this calculation. Results showed possibility of effective hyperthermia using this system through evaluation experiments.

Electrocardiogram measurement during sleep with wearing clothes using capacitively-coupled electrodes.

The electrocardiogram (ECG) was measured by non-contact, non-restraint and unconscious method using capacitively-coupled electrodes made of electro-conductive cloth while subjects lay on bed wearing their clothes. These electrodes are very sensitive so measure not only signals but noise. The seat grounded, which arranged under the electrode could suppress noise. Two types of electrode different in length were used, that is long type and short type. Results showed that both electrodes could sense ECG. Noise generated from e.g. commercial power source was almost the same for both electrodes though the length of electrode was longer than the subject for the long type electrode. Setting position was rather serious and noise component changed greatly by the part of body that touches the electrode. Next, ECG was measured on these condition participants lay with supine position, prone position, right lateral position and left lateral position. The ECG was measured on each condition.

Measurement of human gastric motility by near-infrared light for the assessment of chronic mental stress.

In this study, we focused on the relationship between mental stress and gastric motility and have tried to develop a measurement system of human gastric motility for the quantification of mental stress. A mental stress measurement system should be used easily in daily life. However, general measurement system as electrogastrography, endoscopy, CT, ultrasonic echogram isn't suitable for the home use. Then, we have developed non-invasive and compact measurement system of gastric motility using near-infrared (NIR) light. This system consists of NIR LEDs and an avalanche photodiode (APD). APD receives the NIR light transmitting outside the body from NIR LEDs and reflecting on the gastric wall. In the experiment, an ultrasonic echogram was used simultaneously to confirm our new method. The result showed that the waveform got by our method coincides with the cycle of contractile activity of stomach, and it was proved that our measurement system using NIR light could measure gastric motility. In addition, we performed chronic mental stress measurement intended for students to examine relationship between chronic mental stress and gastric motility. Experimental period was from two weeks before graduation examination to two weeks after graduation examination. The result showed that chronic mental stress may invoke gastric dysrhythmia, and chronic mental stress could be evaluated by long term monitoring of gastric motility using our NIR measurement system.