# Lower- Limb Exosuits for Rehabilitation or Assistance of Human Movement: A Systematic Review
## 1 Introduction  
A wide range of respiratory, cardiovascular, musculoskeletal and neurological diseases can affect mobility [1], impeding various activities of daily living and productive tasks. It has been shown that the ability to walk is likely the mobility factor that influences the physical and mental health-related quality of life the most [1]. An epidemiology study in the USA showed that in 2016 an estimated 61.4 million noninstitutionalized adults reported a disability, with mobility leading as the most prevalent type (13.7%) [2]. In Europe, about one third (32.3%) of adults aged 75 years or older and 10.5% of adults aged 65-74 years reported severe difficulties in walking [3]. With the increase in the older population, the problem of mobility will become more prevalent. In Europe, for example, in 2050 the number of people aged 75-84 years is expected to increase by 56.1% and people aged 65-74 years by 16.6%, compared to 2019 [4]. Given the prevalence of mobility disorders, the foreseen increase in cases due to an aging population and their impact on quality of life, it is of highest interest to rehabilitate orassist walking to restore mobility. In recent years, the field of robotics has advanced significantly to assist the recovery of lower-limb motor function [5]. Compared to conventional therapies, rehabilitation robotics allows the alleviation of the work of health care personnel, permits longer rehabilitation sessions for the patient, can be monitored, controlled and quantified reliantly and can provide an increased motivation by use of gamification. Of special interest are robotic lower-limb exoskeletons, which are worn by a user, fit externally to the body and work in coordination with the user's movement [6]. Powered exoskeletons generally have a rigid supporting structure and actuators that assist movement in users who might have little to no remaining motor function in their lower limbs. The nature of their rigid structures and the necessity for a power supply make robotic rigid exoskeletons cumbersome, decreasing their overall functionality and movement range. To overcome the restrictions of rigid systems, soft exoskeletons (or \"exosuits\") have been developed, where weight-bearing relies on the user's skeletal structure alone. Exosuits reduce weight and minimize limitations in movement by the use of fabric harnesses and low-profile actuation systems. Their greater flexibility provides a larger tolerance for misalignment with the user's skeletal system compared to rigid exoskeletons [7]. As a result, exosuits may facilitate a more natural interaction with the dynamics of walking [8]. Several exosuit models have been developed and published, e.g., Body Braid [9], Superflex [10] or \"ReStore(tm) Soft Exo-Suit\" [11]. To gather evidence about the functionality and benefits of exosuits, it is important to provide peer-reviewed studies that show the effects on the impaired user. General reviews about exoskeletons have been published, mentioning the research in exosuits, but without going into further details on their technological aspects and clinical outcomes [12; 13]. Several reviews have recently been published that specifically analyze exosuits. For example, [PERSON] et al. [14] show an overview of different technological aspects of exosuits, [PERSON] et al. [15] review the design challenges for exosuits, [PERSON] et al. [16] provide an in-depth explanation of construction and control schemes of soft assistive robots, while [PERSON] et al. [17] compare different sensor technologies for exosuits. However, thus far none of the published reviews shows the clinical outcomes of lower-limb exosuits, which are an important indicator for the state of development and foreseeable impact on the health sector.