Use of induced acceleration to quantify the (de)stabilization effect of external and internal forces on postural responses

Due to the mechanical coupling between the body segments, it is impossible to see with the naked eye the causes of body movements and understand the interaction between movements of different body parts. The goal of this paper is to investigate the use of induced acceleration analysis to reveal the causes of body movements. We derive the analytical equations to calculate induced accelerations and evaluate its potential to study human postural responses to support-surface translations. We measured the kinematic and kinetic responses of a subject to sudden forward and backward translations of a moving platform. The kinematic and kinetics served as input to the induced acceleration analyses. The induced accelerations showed explicitly that the platform acceleration and deceleration contributed to the destabilization and restabilization of standing balance, respectively. Furthermore, the joint torques, coriolis and centrifugal forces caused by swinging of the arms, contributed positively to stabilization of the center of mass. It is concluded that induced acceleration analyses is a valuable tool in understanding balance responses to different kinds of perturbations and may help to identify the causes of movement in different pathologies

Design and Evaluation of the LOPES Exoskeleton Robot for Interactive Gait Rehabilitation

This paper introduces a newly developed gait rehabilitation device. The device, called LOPES, combines a freely translatable and 2-D-actuated pelvis segment with a leg exoskeleton containing three actuated rotational joints: two at the hip and one at the knee. The joints are impedance controlled to allow bidirectional mechanical interaction between the robot and the training subject. Evaluation measurements show that the device allows both a "pa- tient-in-charge" and "robot-in-charge" mode, in which the robot is controlled either to follow or to guide a patient, respectively. Electromyography (EMG) measurements (one subject) on eight important leg muscles, show that free walking in the device strongly resembles free treadmill walking; an indication that the device can offer task-specific gait training. The possibilities and limitations to using the device as gait measurement tool are also shown at the moment position measurements are not accurate enough for inverse-dynamical gait analysis

Effect of tsDCS applied with different electrode configurations on the lumbar spinal circuits

Spinal Cord Injury (SCI) is a severe injury to the central nervous system (CNS) which, despite a heavy post injury rehabilitation regime, often leaves patients bound to a wheelchair or with other impairments diminishing their quality of life. Trans-spinal direct current stimulation (tsDCS) is a promising new technique for the treatment of SCI. During tsDCS a small direct current is applied to the spinal cord via two or more stimulation electrodes, placed over the backbone of a subject. The technique aims to alter the response of the neural pathways in the spinal cord, which is hypothesized to have a positive effect on the recovery of the damaged spinal cord neuronal networks. The objective of this study, is to assess how tsDCS modulates the excitability of the spinal cord and whether this modulation is dependent on the electrode placement configurations. The primary goal is to compare a new electrode placement configuration with one that is commonly used in previous tsDCS studies. This is assessed using the H- Reflex, whereby the novel configuration is hypothesized to have a larger modulatory effect on the spinal circuits. The two different configurations are: 1) cathode and anode placed on the T11 vertebra and the left shoulder blade respectively (commonly used) and 2) the two electrodes placed over the spinal cord, 7 centimeters apart and centered around the 11 thoracic vertebra. TsDCS is applied on the lumbar spinal cord for a period of 15 minutes with a current of 2,5mA. The ascending part of the H-reflex recruitment curve is measured before, during and after tsDCS. We hereby present the outcome of the aforementioned study as well as the current progress of our laboratory with respect to the effect of tsDCS on the spinal circuits. We hope that our work will be able to contribute to the effectivity of tsDCS, which could possibly be applied in the rehabilitation of spinal cord injured subjects in the future

Technical validation of a body-weight controlled clutch for ankle-foot orthoses of children with cerebral palsy

[Abstract] Ankle-foot orthoses (AFOs) greatly improve gait in patients with Cerebral Palsy (CP). Some AFO designs allow for passive push-off support, however, these often limit the ankle’s ROM during the swing phase of gait. This contribution presents the technical validation of a body-weight controlled clutch (BWC) designed for children with CP, to passively engage and disengage the push-off support without restricting ankle kinematics. We determined the friction coefficient (μ) of different BWC prototypes, and used it as an indicator for the amount off force that can be exerted on the mechanism before slippage occurs. Four clutch configurations were tested, containing a rigid or flexible spacer and a nylon strapping webbing or neoprene rubber slider. The best tested configuration was the one composed by the rigid spacer–nylon slider combination, which yielded a μ as high as 0.98. We envision that a lightweight solution like the BWC presented here can benefit new AFO designs to support push-off on children with gait deficiencies.Royal Netherlands Academy of Arts & Sciences; KNAWWF/1327/TMB202101Dutch Research Council; 1807

Comparación de dos principios de diseño de órtesis de tobillo no actuadas para asistir en la fase de propulsión: un estudio de caso

[Resumen] La propulsión que ejerce el tobillo es esencial para la ejecuci´on de una marcha humana eficiente. En los últimos años, se han venido aplicando diversos principios de funcionamiento a las ortesis de tobillo y pie (AFO), con el fin de mejorar el trabajo de los músculos flexores plantares y lograr así una propulsión adecuada durante la marcha. Es difícil comparar la ejecución y eficacia de los diferentes diseños debido a que los investigadores no siguen un conjunto estandarizado de criterios y procedimientos comunes. Esto lleva a la realización de una amplia gama de pruebas, con variaciones en factores importantes como la velocidad de marcha y la asistencia proporcionada, lo que afecta en gran medida a la cinemática y la cinética de los usuarios. Este trabajo está enfocado a comprender las posibilidades y los potenciales beneficios de dos importantes principios de diseño para asistir la propulsión del tobillo con una AFO no actuada. Para ello, presentamos y evaluamos dos prototipos de AFO con resorte paralelo al tendón de Aquiles, basados en: (i) un resorte de compresión lineal, y (ii) una transmisión no lineal y personalizada de leva con resorte de ballesta. Se presentan los efectos de ambas AFOs para un estudio de caso con un usuario sano usando ambos prototipos a dos velocidades de marcha bajo las mismas condiciones experimentales. Se encontraron grandes reducciones en la actividad muscular cuando el usuario recibió asistencia, y la cinemática del tobillo estuvo influenciada por los diferentes principios de dicha asistencia. Este estudio de caso fue pensado como un primer intento para proporcionar información sobre cómo dos principios prometedores pueden asistir de forma pasiva la propulsión de tobillo durante la marcha.[Abstract] Ankle propulsion is essential for efficient human walking. In recent years, several working principles have been investigated and applied to ankle-foot orthoses (AFOs) to enhance the work of the plantarflexor muscles and achieve proper propulsion during gait. Comparing the performance and effectiveness of different designs is difficult because researchers do not have a standardized set of criteria and procedures to follow. This leads to a wide range of tests being conducted, with variations in important factors such as walking speed and assistance provided, which greatly affect users’ kinematics and kinetics. In this work, we try to better understand the possibilities and potential benefits of two of the most important design principles for supporting ankle propulsion with unpowered AFOs. To do so, we present and evaluate two AFO prototypes with springs parallel to the Achilles tendon based on: (i) a linear compression spring, and (ii) a customized leaf spring-cam transmission with a nonlinear ankle torque–angle curve. The effects of both AFOs are reported for a case study with one healthy user using both prototypes at two walking speeds under the same experimental conditions. Large reductions in muscular activity were found when the user received assistance, and ankle kinematics were influenced by the different assistance principles. This case study was intended as a first attempt to provide insights on how two promising principles can passively support push-off during gait.Países Bajos. Dutch Research Council NWO; Veni-TTW- 2020 18079Países Bajos. Royal Netherlands Academy of Arts & Sciences; KNAWWF/1327/TMB20210

Effects of a neuromuscular controller on a powered ankle exoskeleton during human walking

Wearable devices to assist abnormal gaits require controllers that interact with the user in an intuitive and unobtrusive manner. To design such a controller, we investigated a bio-inspired walking controller for orthoses and prostheses. We present (i) a Simulink neuromuscular control library derived from a computational model of reflexive neuromuscular control of human gait with a central pattern generator (CPG) extension, (ii) an ankle reflex controller for the Achilles exoskeleton derived from the library, and (iii) the mechanics and energetics of healthy subjects walking with an actuated ankle orthosis using the proposed controller. As this controller was designed to mimic human reflex patterns during locomotion, we hypothesize that walking with this controller would lead to lower energetic costs, compared to walking with the added mass of the device only, and allow for walking at different speeds without explicit control. Preliminary results suggest that the neuromuscular controller does not disturb walking dynamics in both slow and normal walking cases and can also reduce the net metabolic cost compared to transparent mode of the device. Reductions in tibialis anterior and soleus activity were observed, suggesting the controller could be suitable, in future work, for augmenting or replacing normal walking functions. We also investigated the impedance patterns generated by the neuromuscular controller. The validity of the equivalent variable impedance controller, particularly in stance phase, can facilitate serving subject-specific features by linking impedance measurement and neuromuscular controller