## 2 Materials & Methods
### Experimental Protocol  
To verify the effectiveness of the KAEGO system for gait rehabilitation, a 6 min walking test was conducted on one paraplegic patient with incomplete SCI. For the subject's safety, the experiment was conducted based on guidelines (RERI-IRB-200318-2), pre-approved by the Rehabilitation Engineering Research Institute ethics committee. The patient consented to participate in the study, which was conducted under the guidance of a professional therapist. The patient who participated in the experiment had been training with the non-powered EGO (RGO) for many years, so he adapted quickly to the new KAEGO system. He was, therefore, a suitable subject for the comparative evaluation of KAEGO with the non-powered orthosis. The characteristics of the subject have been summarized in Table 3.  
KAEGO was manufactured by installing two knee actuation modules and a control module with a battery in the non-powered EGO that the subject had been using for training. Accordingly, the weight of KAEGO was 13.85 kg, which was approximately 5.5 kg higher than that of the non-powered orthosis. The 6 min walking test is widely used to evaluate the physical activity in patients by comparing their metabolic consumption [1; 19]. In this study, a walking test was conducted under three conditions: (i) wearing non-powered EGO vs. KAEGO; (ii) setting the knee-assisting torque to approximately 25% (5 Nm); and (iii) approximately 100% (20 Nm) of the rated torque. The detailed user customized torque data for the gait experiment are defined in Table 4. The changes in metabolic cost, walking speed, and the distance traveled in patients with these three EGOs were compared. Before the experiment, the participant trained for 60 min per session, three sessions a week, and for at least 10 sessions to adapt to each system. In addition, a preliminary test was conducted once on the day of the experiment so that the participant could fully understand the protocol. The equipment used in the experiment was K4b2 (Cosmed, Roma Italy) [20], which was used to calculate the metabolic cost by measuring the subject's oxygen consumption (VO2) and heart rate (HR), as shown in Figure 9a. Figure 9b shows the 60 m track around which the patient walked at a comfortable speed for 6 min and measured the walking energy efficiency. Each experiment was conducted three times. \begin{table}
\begin{tabular}{c c c c c c} \hline \hline  & **Rising** & **Peak** & **Falling** & **Max.** & **Min.** \\  & **Time (ms)** & **Time (ms)** & **Time (ms)** & **Torque (Nm)** & **Torque (Nm)** \\ \hline
25\% assist & 50 & 20 & 50 & 5 & 2.5 \\
100\% assist & 50 & 150 & 50 & 20 & 0.5 \\ \hline \hline \end{tabular}
\end{table} 
Table 4: The user customized torque profile definitions for the gait experiment. \begin{table}
\begin{tabular}{c c c c c} \hline \hline  & **Parameters** & **SWF** & **SWE** & **STF** & **STE** \\ \hline \(k\) & Nm/deg & 0 & 0 & 0.72 & 0.72 \\ \(d\) & Nms/deg & 0 & 0 & 0.143 & 0.143 \\ \(\theta_{e}\) & deg & 80 & 10 & 10 & 10 \\ \(\tau_{cu}\) & Nm(max.) & 20 & \(-5\) & 0 & 0 \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Impedance parameters for the four gait modes using the knee-actuated-exoskeletal-gait orthosis (KAEGO). \begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Gen.** & **Age** & **Height** & **Weight** & **Injury Level** & **ASIA** & **Onset** \\ \hline M & 45 & 163 cm & 66 kg & L1 & C & 2004 \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Characteristics of the patient with an incomplete spinal cord injury (SCI). The metabolic cost of transport (COT) while walking has been applied to quantitatively evaluate the walking efficiency of patients with incomplete SCI and wearing the proposed exoskeleton system [10]. This metabolic COT quantifies the energy required to move an individual or object from one place to another and is widely used as a method for evaluating human walking efficiency [21]. It is calculated by normalizing the total energy to the distance traveled and the total weight.