Electrical Stimulation Intensity to Induce Sensory Reweighting Dynamics While Standing on Balance Board.

In human postural control, maladaptation of sensory reweighting to sudden environmental changes is one of the main causes of postural instability. Providing sensory cues for body motion by means of stimulation could induce the sensory reweighting dynamics. In this paper, we aimed to investigate the intensity level of electrical stimulation to induce sensory reweighting dynamics while standing on a balance board under three conditions: no stimulation (control), electrotactile stimulation (ETS) at a low-intensity level, and electrical muscle stimulation (EMS) at a high-intensity level. A total of 30 participants (ten for each condition) controlled their posture to keep the board horizontal in a balance-board task, which included a pre-test without stimulation, a stimulation test, and a post-test without stimulation. The EMS and ETS groups received electrical stimulation to the tibialis anterior or soleus muscles based on the board tilt. Before and after the balance-board task, participants performed static standing with their eyes open and also with their eyes closed to evaluate the visual reweighting. In the EMS group, the visual reweighting showed a strong negative correlation with the balance-board sway ratio between the pre- and stimulation tests, indicating that EMS induced a tendency that requires visual up-weighting to improve postural balance. However, there were no significant correlations between either parameter in the control and ETS groups. These results suggest that high-intensity electrical stimulation at the level of directly contracting muscles may be effective in reliably inducing sensory reweighting dynamics, while low-intensity electrical stimulation may be insufficient.Clinical relevance- These findings will be helpful for designing stimulus conditions to reliably induce the reweighting during balance training, and for establishing a new balance training method utilizing EMS to induce visual up-weighting.

Induced effects of electrical muscle stimulation and visual stimulation on visual sensory reweighting dynamics during standing on a balance board.

Providing instruction cues on body motions using stimulations has the potential to induce sensory reweighting dynamics. However, there are currently very few quantitative investigations on the difference in the induced effects on the sensory reweighting dynamics between stimulation methods. We therefore investigated the difference in the induced effects of electrical muscle stimulation (EMS) and visual sensory augmentation (visual SA) on sensory reweighting dynamics during standing on a balance board. Twenty healthy participants controlled their posture to maintain the board horizontally in the balance-board task, which included a pre-test without stimulation, a stimulation test, and a post-test without stimulation. The EMS group (n = 10) received EMS to the tibialis anterior or soleus muscle based on the board tilt. The visual SA group (n = 10) received visual stimuli via a front monitor based on the board tilt. We measured the height of the board marker and calculated the board sway. Before and after the balance-board task, the participants performed static standing with their eyes open and closed. We measured postural sway and calculated the visual reweighting. The visual reweighting showed a strong negative correlation with the balance board sway ratio between the pre- and stimulation tests in the EMS group and a strong positive correlation with that in the visual SA group. Moreover, for those who reduced the balance board sway in the stimulation test, the visual reweighting was significantly different between the stimulation methods, demonstrating that the induced effect on sensory reweighting dynamics is quantitatively different depending on which method is used. Our findings suggest that there is an appropriate stimulation method to change to the targeted sensory weights. Future investigations on the relationship between sensory reweighting dynamics and stimulation methods could contribute to the proposal and implementation of new training methods for learning to control the target weights.

Force Control on Fingertip Using EMS to Maintain Light Touch.

Light touch on a rigid surface with minimal force below a specific threshold reduces postural sway by providing additional sensory cues from the fingertips. The feasibility of maintaining light touch depends on subject characteristics and task difficulty. Therefore, we introduce a method of maintaining light touch by using electrical muscle stimulation (EMS). We applied it in a single-leg standing task involving healthy adult subjects. The subjects stood upright in a single-leg stance on a firm surface and on foam rubber (FR), respectively, under three conditions: no touch (NT, NT-FR), light touch without EMS (LT, LT-FR), and light touch in which EMS was applied based on the contact force (LT-EMS, LT-EMS-FR). The results showed that the force control by EMS helped maintain light touch and reduce postural sway compared with the no-touch condition. The amplitude of postural sway under the touch condition with EMS was equivalent to that under the touch condition without EMS.

Correction of Electrode ID Configuration based on Distribution of Surface EMG Features.

Surface EMG (sEMG) signals are useful for estimating the motion or exercise of users. Wireless-type sensor electrodes, which are placed on multiple parts of the body and send the measured signals to a server, have recently become commercially available. With many estimation algorithms, the relationships between the sensor IDs and the body parts they are placed on (ID configuration) are expected to be fixed between the calibration and estimation phases. If the ID configuration is changed after the calibration phase, the estimation accuracy tends to dramatically decrease. Since it is inconvenient for users to check the ID configuration every time, we developed a method to correct the electrode ID configuration on the basis of the distribution of sEMG features. Using open data, we investigated the feasibility of our method by shuffling the order of sEMG signals. The results showed that the method was able to correct the ID configuration and restore the estimation accuracy to close to that of the calibration.

Sock-Type Wearable Sensor for Estimating Lower Leg Muscle Activity Using Distal EMG Signals.

Lower leg muscle activity contributes to body control; thus, monitoring lower leg muscle activity is beneficial to understand the body condition and prevent accidents such as falls. Amplitude features such as the mean absolute values of electromyography (EMG) are used widely for monitoring muscle activity. Garment-type EMG measurement systems use electrodes and they enable us to monitor muscle activity in daily life without any specific knowledge and the installation for electrode placement. However, garment-type measurement systems require a high compression area around the electrodes to prevent electrode displacement. This makes it difficult for users to wear such measurement systems. A less restraining wearable system, wherein the electrodes are placed around the ankle, is realized for target muscles widely distributed around the shank. The signals obtained from around the ankle are propagated biosignals from several muscles, and are referred to as distal EMG signals. Our objective is to develop a sock-type wearable sensor for estimating lower leg muscle activity using distal EMG signals. We propose a signal processing method based on multiple bandpass filters from the perspectives of noise separation and feature augmentation. We conducted an experiment for designing the hardware configuration, and three other experiments for evaluating the estimation accuracy and dependability of muscle activity analysis. Compared to the baseline based on a 20-500 Hz bandpass filter, the results indicated that the proposed system estimates muscle activity with higher accuracy. Experimental results suggest that lower leg muscle activity can be estimated using distal EMG signals.

Lower Limb Muscle Activity Control by using Jamming Footwear.

To change the lower limb muscle activities while walking, we propose a muscle activity controlling system that dynamically changes shoe insoles. We conducted a preliminary experiment on a prototype system to determine the system's validity. In this experiment, we analyzed how tibialis anterior and gastrocnemius muscle might change their activities depending on each insole condition. The results lead us to conclude that our system may affect changes in the duration percentage of tibialis anterior muscle activation when we change the heel part shape, and that it may change the maximum amplitude of gastrocnemius muscle activation when we change the arch part shape and hardness.

Estimating the lower leg muscle activity from distal biosignals around the ankles.

Electromyogram signals (EMG) can be used not only to measure motions, but also to control devices such as exoskeleton robots. Sensor electrodes need to be placed on each muscle based on kinematics and anatomical characteristics. Wearable EMG measurement approach is also investigated in recent years. Electrodes are fixed to the clothes. In this paper, we propose a motion measurement method based on propagation characteristics of biopotential signal. An experiment with walking and plantar flexion motion as tasks. The results showed that the signals calculated from proposed method were comparable with that of conventional method. We confirmed that there were few individual differences for calculating the signals of tibialis anterior, gastrocnemius and peroneal muscles.

Robot assisted physiotherapy to support rehabilitation of facial paralysis.

We have been developing the Robot Mask with shape memory alloy based actuators that follows an approach of manipulating the skin through a minimally obtrusive wires, transparent strips and tapes based pulling mechanism to enhance the expressiveness of the face. For achieving natural looking facial expressions by taking the advantage of specific characteristics of the skin, the Robot Mask follows a human anatomy based criteria in selecting these manipulation points and directions. In this paper, we describe a case study of using the Robot Mask to assist physiotherapy of a hemifacial paralyzed patient. The significant differences in shape and size of the human head between different individuals demands proper customizations of the Robot Mask. This paper briefly describes the adjusting and customizing stages employed from the design level to the implementation level of the Robot Mask. We will also introduce a depth image sensor data based analysis, which can remotely evaluate dynamic characteristics of facial expressions in a continuous manner. We then investigate the effectiveness of the Robot Mask by analyzing the range sensor data. From the case study, we found that the Robot Mask could automate the physiotherapy tasks of rehabilitation of facial paralysis. We also verify that, while providing quick responses, the Robot Mask can reduce the asymmetry of a smiling face and manipulate the facial skin to formations similar to natural facial expressions.