## 2 Materials and Methods
### Soft Passive Exoskeleton  
A soft passive exoskeleton made of elastic (Lycra) fabric woven with carbon thread was used. The textile module of this exoskeleton has a specific tension and force direction that is useful in ensuring the patient's body alignment in three-dimensional space. These typically extend from the shoulders to the hips, creating a force that opposes trunk movements (Figure 1). The passive exospine designed to be accommodated in the patient's spine using optoelectronic methods [34] is attached to the textile module. Two different versions of the exospine, one more flexible (MFE) and one less flexible (LFE), were used and personalized to subjects' characteristics, fitting perfectly to the posterior surface of the trunk. Because these devices are typically made of shape memory material, they operate on the principle of energy restitution. The MFE and LFE exospines are made up of a sequence of plastic vertebrae and rubber discs (vulkoltan 65 shore and 90 shore, respectively) stacked with a pair of harmonic long steel wires with a thickness of 2 mm and 3 mm, respectively (Figures 2 and 3A). \begin{table}
\begin{tabular}{c|c c c c c} \hline
**Patients** & **Age** & **Gender** & **Diagnosis** & **SARA Tot** & **SARA Gait** \\ \hline P1 & 67 & F & SAOA & 18 & 4 \\ P2 & 57 & F & SAOA & 5 & 2 \\ P3 & 37 & M & SCA1 & 14 & 3 \\ P4 & 54 & M & SCA2 & 14 & 3 \\ P5 & 59 & M & SAOA & 12 & 3 \\ P6 & 51 & M & SAOA & 7 & 2 \\ P7 & 66 & M & SCA40 & 6 & 2 \\ P8 & 53 & F & SCA1 & 2 & 1 \\ P9 & 55 & M & SCA1 & 2 & 1 \\ \hline \end{tabular}
\end{table} 
Table 1: Patients’ characteristics. Figure 1: Textile module made of Lycra fabric woven with carbon thread; soft passive exoskeleton. Figure 3: Experimental setup with device position during measurement and corresponding axis of orientation (**A**). Relation between torque and position of topmost vertebrae for more flexible (**B**) and less flexible (**C**) exoskeleton. Figure 2: Exospine design with plastic vertebrae, rubber discs, and harmonic long stile wires. Energy storage allows the generation of moments for each element, plastic vertebrae–rubber discs–plastic vertebrae, represented in the figure with red circle (right side). Exospines Laboratory Tests  
Both exospines were firmly fixed to the table with a 3D printed clamp on their lowest vertebrae. Each vertebra (Figure 3) had a single Optotrak (NDI, Waterloo, ON, Canada) marker on it (3D Accuracy 0.1 mm, resolution 0.01 mm), and only the topmost vertebrae on both devices had an Optotrak marker rig which also enables rotation measurements of the topmost vertebrae. Optotrak camera was placed 2.2 m from the device in positive \(y\)-axis (Figure 3A). The force was measured with a beam loadcell TAL220 (SparkFun Electronics, China; 10 kg capacity rating). The loadcell was connected to the top vertebrae with a non-flexible 50 cm long steel wire. Each device has a maximum bend angle which should not be exceeded to prevent irreversible plastic deformation (20\({}^{\circ}\) for the MFE and 26\({}^{\circ}\) for the LFE from rest position). The loadcell was connected to a multichannel amplifier (Burster 9236, Burster Italia, Curno, Italy), and from there to a NI (Austin, TX, USA) USB 6008 DAC and PC via USB cable. Data were recorded using Simulink (version 7.10.0, MathWorks, Natick, MA, USA). Data from the loadcell and Optotrak were synchronized during measurements. Optotrak has a trigger signal output used, via the NI DAC, as a trigger in Simulink to start recording loadcell data at the same time as the Optotrak system does. The sampling frequency of the loadcell and Optotrak was 100 Hz. The loadcell was calibrated using known weights and, during all measurements, the steel wire was always parallel to the table. Recorded data were filtered using a low-pass 4 th order Butterworth filter with a 5 Hz cut-off frequency.