# Development and Preliminary Evaluation of a Lower Body Exosuit to Support Ankle Dorsiflexion
Due to the stiffness of the material, often plastic or carbon [18; 19], the user has to preload the material, in order to release the energy afterwards. In the case of a passive ankle orthosis for assisting the foot lifting, the user needs additional muscle force to deform the material and increase strain that is used in the other direction to support the dorsiflexion. Consequently, patients with a lack of neuromuscular activity may be hindered in generating an adequate propulsion impulse. Although passive orthosis should improve ankle mobility, the stiff structure could lead to a converse effect with immobilization of the ankle joint following muscle atrophy. Regarding the development process, different structural analyses and design methods with various material thickness and shapes have been tested [20] to fit wearers' ankles and feet. Nevertheless, [PERSON] et al. [13] found no difference between bespoke versus off-the-shelf orthosis for gait impairment parameters or satisfaction of stroke survivors. Especially for wearing the orthosis in daily life, wearing comfort is an important requirement, but due to the material of passive AFOs, they often induce pressure points on the body [21]. Consequently, patients might refuse wearing the aids because of uncomfortable usage. Besides passive orthosis, active exoskeletal devices have the potential to provide immediate assistance during gait. These active devices with incorporated control (e.g., [PERSON] et al. [22], [PERSON] et al. [23]) allow changes in their impedance and therefore offer gait-adapted assistance. In contrast to passive orthosis, the active performance could help with re-educating the neuromotor system and facilitate the rehabilitation process [24]. Nevertheless, many of these devices are characterized by a rigid, heavyweight and overhanging design with parallel acting system joints, where a majority of the weight is located on distal joints [25], which might inhibit the natural freedom of movement [26]. Currently, more novel, lightweight and soft wearable designs, so called exosuits, are demonstrated to overcome the disadvantages of passive orthosis and heavy active devices by combining innovative textiles with lightweight actuators. By the use of soft structures and tensile forces, it is feasible to overcome the limitation of reproducing the complex kinematic structure of the ankle as a parallel-acting kinematic mechanism with the risk of misalignment of mechanical axis and human joint [27]. Thus, exosuits often introduce minimal changes to wearers' natural gait because of a biomimetic design comprising of flexible textiles. [PERSON] et al. [28] present a soft, non-restrictive and active exosuit with the possibility to use in everyday life. It combines support of dorsiflexion and plantarflexion and therefore improves the ankle's swing phase, forward propulsion interlimb asymmetry and energy cost of walking. [PERSON] et al. [29] shows an exosuit with multi-joint assistance, which provides synchronized force to the hip and ankle joint during walking. Besides the usage in rehabilitation, other fields of applications may be considered, as this system can reduce metabolic cost and improve walking efficiency when carrying load. An important feature of active gait support devices for training or daily use is the ability to adapt to different walking conditions, such as level walking or stair ascent and descent. A lot of existing devices are characterized by a complicated design using many sensors, which requires complex control algorithms [30]. Different control strategies can be found in the literature, such as fuzzy logic control [31], PID (position) control [32], adaptive control [33] and inverse dynamics control [34]. Unfortunately, an increase in complexity of control systems through multiple sensors and impedances does not ensure the best solution for orthotic devices, because they are becoming cost-intensive and not suitable for daily use [35].