# Lower- Limb Exosuits for Rehabilitation or Assistance of Human Movement: A Systematic Review
## 3 Review
### Exosuit Technology  
Information of the technological features extracted from the studies is presented in Table 3. Lower-limb exosuits can address any combination of the articulations of hip, knee  
Figure 2: (**a**) Number of relevant publications per year, separated by impaired and healthy test subjects; (**b**) tree map chart of articulations addressed by the exosuits by number of publications; (**c**) actuator types used for force generation by number of publications; (**d**) techniques of force translation employed by number of publications; (**e**) sensor types used for measurement in the exosuits; (**f**) percentage of studies by impairment; and (**g**) percentage of users enrolled by different impairments. and ankle. Of the identified studies, 21% addressed two or more articulations. Single articulation studies were the most common ones (79%), with a focus on ankle (58%) and knee (21%). Figure 2b shows the number of studies addressing articulations and their combinations. The complexity of exosuits is influenced by the number of addressed joints and the technical implementation of their control architecture, including sensors and controllers. Examples of levels of complexity are shown in Figure 3. Reviewed studies are mostly focused on single-articulation exosuits, which is explained by the increasing complexity when creating multi-articulation setups. The control of multiple articulations during a movement is difficult to design and the interplay of the exosuit and the user is hard to predict. Considering the rise in interest of the topic and ongoing studies of exosuits, it is foreseeable that with the accumulation of study results, multi-articulation setups are going to become more common. Figure 3: Examples of lower-limb exosuit devices: (**a**) Passive knee sleeve with pneumatic chambers (reproduced from [26]), (**b**) passive elastic ankle brace (reproduced from [27]), (**c**) active ankle assistive exosuit (reproduced from [28]). \begin{table}
\begin{tabular}{c c c c c c c c c c c} \hline \hline
**ID** & **Year** & **Articulations** & **Power Type** & **Weight** & \ \begin{tabular}{c} **Tefined (r)/** \\ **Uattehered (t)** \\ \end{tabular}  & **Arctuators** & \begin{tabular}{c} **Type of Force** \\ **Transmission on** \\ **Body** \\ \end{tabular}  & **Sensor Types/Application** & **Control Scheme \({}^{*}\)** \\ \hline [PERSON] et al. [59] & 2020 & Ankle & Active & 5 kg & U & Electric & Bowden cables & Gyroscope, load cells/Identify & \\  & & & & & & & & & \\  & & & & & & & & & \\  & & & & & & & & & \\  & & & & & & & & & \\  & & & & & & & & & \\ \hline [PERSON] et al. [28] & 2020 & Ankle & Active & \textless{5 kg} & U & Electric & Bowden cables & Gyroscope, load cells/Identify & \\  & & & & & & & & & \\  & & & & & & & & & \\  & & & & & & & & & \\  & & & & & & & & & \\  & & & & & & & & & \\ \hline [PERSON] et al. [0] & 2017 & Ankle & Active & \textless{0.9 kg} & T & Electric & Bowden cables & Gyroscope, load cells/Identify & \\  & & & & & & & & & \\  & & & & & & & & & \\  & & & & & & & & & \\  & & & & & & & & \\  & & & & & & & & & \\  & & & & & & & & \\  & & & & & & & & & \\  & & & & & & & & \\  & & & & & & & & & \\  & & & & & & & & & \\  & & &  
Studies included in this review used active and passive exosuits (9 and 10 studies, respectively). Actuator types used in the active exosuits are electric motors (89%) and pneumatic actuators (11%) (see Figure 2c). None of the publications stated the amount of power consumed by the active exosuits. From all included studies, three used exosuits that had to be tethered to an external power source or air compressor, while 16 were untethered. All passive exosuits were untethered, compared with six out of nine active exosuits. Several types of force transmission were used to transmit displacements and forces from an actuator to the body. Bowden cables and elastic materials were the most frequently used type for force transmission (42% each), followed by pneumatic inflatable structures (11%) and springs (5%) (see Figure 2d).