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[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.

Series elastic actuators (SEA) with their inherent compliance offer a safe torque source for robots that are interacting with various environments, including humans. These applications have high requirements for the SEA torque controllers, both in the torque response as well as interaction behavior with its environment. To differentiate state of the art torque controllers, this work introduces a unifying theoretical and experimental framework that compares controllers based on their torque transfer behavior, their apparent impedance behavior, and especially the passivity of the apparent impedance (i.e., their interaction stability) as well as their sensitivity to sensor noise. We compare classical SEA control approaches such as cascaded PID controllers and full state feedback controllers with advanced controllers using disturbance observers, acceleration feedback and adaptation rules. Simulations and experiments demonstrate the trade-off between stable interactions, high bandwidths and low noise levels. Based on these trade-offs, an application-specific controller can be designed and tuned, based on desired interaction with the respective environment., Support Biomechanical Engineering

Background: Spasticity, i.e. stretch hyperreflexia, increases joint resistance similar to symptoms like hypertonia and contractures. Botulinum neurotoxin-A (BoNT-A) injections are a widely used intervention to reduce spasticity. BoNT-A effects on spasticity are poorly understood, because clinical measures, e.g. modified Ashworth scale (MAS), cannot differentiate between the symptoms affecting joint resistance. This paper distinguishes the contributions of the reflexive and intrinsic pathways to ankle joint hyper-resistance for participants treated with BoNT-A injections. We hypothesized that the overall joint resistance and reflexive contribution decrease 6 weeks after injection, while returning close to baseline after 12 weeks. Methods: Nine participants with spasticity after spinal cord injury or after stroke were evaluated across three sessions: 0, 6 and 12 weeks after BoNT-A injection in the calf muscles. Evaluation included clinical measures (MAS, Tardieu Scale) and motorized instrumented assessment using the instrumented spasticity test (SPAT) and parallel-cascade (PC) system identification. Assessments included measures for: (1) overall resistance from MAS and fast velocity SPAT; (2) reflexive resistance contribution from Tardieu Scale, difference between fast and slow velocity SPAT and PC reflexive gain; and (3) intrinsic resistance contribution from slow velocity SPAT and PC intrinsic stiffness/damping. Results: Individually, the hypothesized BoNT-A effect, the combination of a reduced resistance (week 6) and return towards baseline (week 12), was observed in the MAS (5 participants), fast velocity SPAT (2 participants), Tardieu Scale (2 participants), SPAT (1 participant) and reflexive gain (4 participants). On group-level, the hypothesis was only confirmed for the MAS, which showed a significant resistance reduction at week 6. All instrumented measures were strongly correlated when quantifying the same resistance contribution. Conclusion: At group-leve, Biomechanical Engineering, Support Biomechanical Engineering

Increasing knowledge on human balance recovery strategies is important for the development of balance assistance strategies using assistive devices like a powered lower-limb exoskeleton. One of the postures which is relevant for this scenario, but underexposed in research, is staggered stance, a posture with one foot in front. We therefore aimed to gain a better understanding of balance recovery in staggered stance. We studied balance responses at joint- and muscle levels to pelvis perturbations in various directions while standing in this posture. Ten healthy individuals participated in this study. We used one actuator beside and one behind the participant to apply 150 ms perturbations in mediolateral (ML), anteroposterior (AP) and diagonal directions, with a magnitude of 3, 6, 9 and 12% of the participant’s body weight (BW). Meanwhile, motion capture, ground reaction forces and moments, and electromyography of the muscles around the ankles and hips were recorded. The perturbations caused movements of the centre of mass (CoM) and centre of pressure (CoP) in the direction of the perturbation. These were often accompanied by motions in a direction different from the perturbation direction. After perturbations perpendicular to the line between both feet, large and significant AP deviations were present of the CoM (-0.27 till 0.40 cm/%BW, p < 0.029) and CoP (-0.99 till 0.80 cm/%BW, p < 0.001). Also, stronger responses on joint and muscle level were present after these perturbations, compared to AP and diagonal perturbations collinear with the line between both feet. The hip, knee and ankle joints contributed differently to the balance responses after the different perturbation directions. To conclude, standing in a staggered stance posture makes individuals more vulnerable to perturbations perpendicular to the line between both feet, requiring larger responses on joint level as well as contributions in the sagittal plane, Support Biomechanical Engineering