# Preliminary Biomechanical Evaluation of a Novel Exoskeleton Robotic System to Assist Stair Climbing
## 2 Materials and Methods
### Participants, Setup and Procedure  
There were three subjects (1 m; 2 f; 26.0 \(\pm\) 3.6 years; 24-31 years; 1.72 \(\pm\) 0.03 m; 70.2 \(\pm\) 6.0 kg) that participated in the preliminary biomechanical study. According to their own statements, each subject was healthy and had no orthopaedic impairments. The relevant anthropometric data of each subject were measured first and is shown in Table 1. The hip joint centres were estimated to determine the hip width [18; 19]. In order to investigate the biomechanical effectiveness of the novel exoskeleton system eBUS, all of the participants performed ascents and descents both without and with eBUS. \begin{table}
\begin{tabular}{c c c c c c c c c c c c} \hline \hline \multirow{2}{*}{**SID**} & \multirow{2}{*}{**A**} & \multirow{2}{*}{**S**} & \multirow{2}{*}{**bm**} & \multirow{2}{*}{**bh**} & \multirow{2}{*}{**hw**} & \multicolumn{4}{c}{**Right Leg**} & \multicolumn{4}{c}{**Left Leg**} \\ \cline{5-12}  & & & & & & & **mtl** & **sl** & **f** & **mtl** & **sl** & **fl** \\ \hline S1 & 31 & m & 76.5 & 1.76 & 0.171 & 0.486 & 0.426 & 0.257 & 0.494 & 0.412 & 0.260 \\ \hline S2 & 24 & f & 62.2 & 1.72 & 0.176 & 0.428 & 0.412 & 0.265 & 0.442 & 0.400 & 0.267 \\ \hline S3 & 23 & f & 71.8 & 1.69 & 0.186 & 0.458 & 0.386 & 0.248 & 0.445 & 0.387 & 0.248 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Relevant anthropometric data of the subjects with SID = subject identification, A = age in years, S = sex (m = male, f = female), bm = body mass [kg], bh = body height [m], hw = hip width [m], mtl = morphological thigh length [m], sl = shank length [m], fl = foot length [m]. Figure 2: Adjustment possibilities on the eBUS exemplary for the left side (**left**) with a detailed view in the frontal plane (**bottom right**) and the adjustable distances (**top right**) [4]: D-A-K (Distance-Ankle-Knee); D-G-A (Distance-Ground-Ankle); D-TS-TR (Distance-ThighSegment-ThighRail); D-SS-SUR (Distance-ShankSegment-ShankUpperRail); D-FS-FR-lat (Distance-FootSegment-FootRail-lateral). For this purpose, a four-step staircase (Figure 3) with a step height of 0.16 m, tread of 0.28 m, and a resulting inclination angle of 30\({}^{\circ}\) was used. In the second step of the staircase is a force plate (MiniDyn type 9119 AA2, Kistler Instrumente AG, Winterthur, Switzerland) is implemented to record the ground reaction force (GRF) at 1500 Hz. A marker-based motion capture system (Qualisys AB, Goteburg, Sweden) with twelve active infrared cameras recorded the kinematics at 100 Hz. For recording and synchronization, the software Qualisys Track Manager 2021 was used. The tensile assistive force in the Bowden cable was recorded through the tension force sensor, which is mentioned above. This force data, together with the data of the inertial measurement units for position determination and the pressure sensors for stands detection, were stored with a time stamp on the internal memories of the eBUS. Furthermore, sEMG signals of the m. vastus medialis (VAM) and m. vastus lateralis (VAL) were measured on both legs using dual electrodes and a wireless measurement system (Noraxon Inc., Scottsdale, AZ, USA). Firstly, the relevant body parameters such as body weight, body height, and segment lengths were measured. Subsequently, the electrodes for the sEMG measurement were placed on the subject according to the senium project [20]. After that, the subjects performed an isolated knee extension within a flexion angle of 90\({}^{\circ}\) to 70\({}^{\circ}\) to determine the maximum voluntary contraction (MVC) of the quadriceps femoris muscles according to [21]. Based on the CAST-model [22] and the placement of two markers on the shoulder, a total of 36 passive infrared markers were applied. Furthermore, eight additional markers were placed medially and laterally on the knee and ankle joints of both legs. The participants then performed six ascents and descents without the exoskeleton, barefoot, at a self-selected speed and climbing step-over-step.