Latin American Applied Research 52(2):89-99 (2022) https://doi.org/10.52292/j.laar.2022.626 89 LOWER LIMB ASSISTANCE SYSTEMS: A STATE OF THE ART M.A. GARCÍA, W.M. ALCOCER, A. BLANCO, A. ABÚNDEZ, C. CORTÉS and J. COLÍN Centro Nacional de Investigación y Desarrollo Tecnológico, Cuernavaca, Mexico. miguel.garcia17me@cenidet.edu.mx Abstract−− In this paper, we present a state of the art regarding lower limb assistance systems. That is, exoskeletons, exosuits, actuated orthoses and smart walkers intended to assist users with or without walk- ing difficulties in such task. We emphasize on those systems headed towards motion intention prediction, especially those that implement myosignals in order to control the system. However, there are some using cortical or encephaloelectric signals. We make clear the importance of developing this technology for the sake of the user’s health, when regarding people with reduced motor capacity. After the reviewed systems, we bring forward our own system intended to assist hemiplegic/hemiparetic patients walking by predict- ing motion intention. The main differentiator of our design shall be energy saving as it is being designed to actuate the hip only during swing phase. Thus, hypo- thetically allowing the system to save ≥60% energy, compared to the same system actuated during the whole walking cycle. Keywords−− Lower limb exoskeleton, motion in- tention prediction, myosignal, walking assistance, en- ergy saving. I. INTRODUCTION Each year the number of people suffering from a lower limb (LL) mobility impairing disease increases. It is know from various medical reports that for people to keep good health it is very important that they to walk correctly (Organización Mundial de la Salud and Banco Mundial, 2011; Westerterp, 2013). Mobility loss affects the patient’s economy, social status and yields negative effects that strike both the pa- tient’s physical and mental health. Such negative effects can derive not from the disease itself but from a poor medical care. Accessing assistance devices that would al- low patients going through a proper rehabilitation pro- cess and/or doing activities of daily living (ADL) inde- pendently would avoid such effects and, in some cases, recover in some grade. Nevertheless, in developing na- tions, only between 5 to 15% of the world population has access to the required attention (World Health Organization, 2013; Chen et al., 2016, 2017). According to the WHO’s 2011 world report on disa- bility (Organización Mundial de la Salud and Banco Mundial, 2011), jointly with The World Bank, disabili- ties have a social and economic negative impact, not only to those suffering from some disability but also their fam- ilies and even their nations. On the same report, and also claimed by the UN, it is estimated that in 2050 22% of the world population will be over 60 years old and 2 bil- lion would be adults with mobility issues affecting their ADL. Furthermore, this rate increases exponentially. There are many reasons leading to lower limb mobil- ity loss: an accident, disease or surgery aftermath. These people, as said before, face not only motor difficulties but a series of social and health problems. Namely, exclusion and discrimination, which, together with motor disability and realizing they need someone else’s assistance, leads them to depression. Moreover, they are also prone to suf- fering back disorders, obesity, cardiovascular diseases, muscle damage, to name a few, due to lack of motion or to unnatural motion (World Health Organization, 2013; Chen et al., 2016, 2017). People suffering from motor disability require reha- bilitation. Such process represents a great burden to the physiotherapist since it takes a large number of repeti- tions. Besides, it is not as effective as desired. That is one reason why experts are proposing mechatronic rehabili- tation devices. This would relieve physiotherapist from the burden and provide the patient with a reliable and ef- ficient rehabilitation (Ai et al., 2018). Even though there are LL orthoses, they still have shortcomes that do not allow the user a natural motion. Moreover, some patients do not have enough strength to seize an orthosis, so it has become necessary to develop more advanced devices that would allow them perform- ing ADL: exoskeletons (World Health Organization, 2013; Chen et al., 2016, 2017). An exoskeleton is a type of assistance/rehabilitation robot that can be worn by a human, as in Fig. 1. It is used to assist motion, whether in rehabilitation process or through ADL or to augment human force (Marcheschi et al., 2011; Lee et al., 2014). Lower limb exoskeletons (LLE) have been devel- oped in late years. Even though there has been great pro- gress, and the use of assistance and rehabilitation robots has been increasing, there are still challenges to over- come: many do not allow performing many tasks, or al- low just a few, they use control strategies based on mo- tion intention prediction (MIP) via myosignals, to offer the patient a more natural motion and control it implicitly with his bare intention, which implies a hard work on cal- ibrating the biosensors and factors that easily induce in- terference on the myosignals. With patients with im- paired motion, it is often complicated, if not impossible in some cases, to obtain a reliable signal. Nonetheless, the use of myosignals to control an LLE is considered one of the most powerful techniques (Harvard, 2017; Farris et al., 2011; Westerterp, 2013; World Health Organiza-