## 4 Discussion  
In this study, we hypothesized that the metabolic cost associated with walking would decrease and walking speed would increase based on the knee joint activation. To verify this hypothesis, a modular knee actuator installed in a non-powered EGO was developed. A walking metabolic cost test demonstrated the effectiveness of the proposed system in one SCI patient with incomplete paraplegia. We found that when the KAEGO was worn, VO\({}_{2}\) and HR showed a small increase, but the distance traveled and walking speed increased significantly. The COT, which indicates the overall energy consumption, decreased by up to 24.5% as the knee assist torque increased. As compare Tables 5 and 7, despite an increase in weight of 5.5 kg \begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Trial** & **COT** & \begin{tabular}{c} **Velocity** \\ **(m/s)** \\ \end{tabular} & \begin{tabular}{c} **VO\({}_{2}\)** \\ **(mL/min/Kg)** \\ \end{tabular} & \
\begin{tabular}{c} **HR** \\ **(bpm)** \\ \end{tabular} &
\begin{tabular}{c} **Distance** \\ **Traveled (m)** \\ \end{tabular} \\ \hline
1 & 9.5 & 0.48 & 15.8 & 130.5 & 170.3 \\
2 & 8.7 & 0.49 & 14.4 & 120.8 & 172.3 \\
3 & 8.5 & 0.50 & 14.3 & 119.1 & 178.0 \\ \hline Mean \(\pm\) SD & 8.9 \(\pm\) 0.4 & 0.49 \(\pm\) 0.01 & 14.8 \(\pm\) 0.7 & 123.5 \(\pm\) 5.0 & 173.5 \(\pm\) 3.3 \\ \hline \hline \end{tabular}
\end{table} 
Table 6: Metabolic cost estimation following the 6 min walking test wearing KAEGO with 25% rated power. \begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Trial** & **COT** & \begin{tabular}{c} **Velocity** \\ **(m/s)** \\ \end{tabular} & \begin{tabular}{c} **VO\({}_{2}\)** \\ **(mL/min/Kg)** \\ \end{tabular} & \
\begin{tabular}{c} **HR** \\ **(bpm)** \\ \end{tabular} &
\begin{tabular}{c} **Distance** \\ **Traveled (m)** \\ \end{tabular} \\ \hline
1 & 8.0 & 0.58 & 15.0 & 117.7 & 209 \\
2 & 8.3 & 0.58 & 16.0 & 124.8 & 213.3 \\
3 & 7.8 & 0.62 & 16.2 & 127.6 & 227 \\ \hline Mean \(\pm\) SD & 8.0 \(\pm\) 0.2 & 0.59 \(\pm\) 0.02 & 15.7 \(\pm\) 0.5 & 123.4 \(\pm\) 4.1 & 216.4 \(\pm\) 7.7 \\ \hline \hline \end{tabular}
\end{table} 
Table 7: Metabolic cost estimation following the 6 min walking test wearing KAEGO with 100% rated power. \begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Trial** & **COT** & \begin{tabular}{c} **Velocity** \\ **(m/s)** \\ \end{tabular} & \begin{tabular}{c} **VO\({}_{2}\)** \\ **(mL/min/Kg)** \\ \end{tabular} & \
\begin{tabular}{c} **HR** \\ **(bpm)** \\ \end{tabular} &
\begin{tabular}{c} **Distance** \\ **Traveled (m)** \\ \end{tabular} \\ \hline
1 & 10.6 & 0.44 & 14.9 & 115.9 & 159.4 \\
2 & 10.4 & 0.44 & 15.2 & 114.3 & 160.3 \\
3 & 11.0 & 0.41 & 14.8 & 113.3 & 154.4 \\ \hline Mean \(\pm\) SD & 10.6 \(\pm\) 0.2 & 0.43 \(\pm\) 0.01 & 15.0 \(\pm\) 0.2 & 114.5 \(\pm\) 1.1 & 158.0 \(\pm\) 2.6 \\ \hline \hline \end{tabular}
\end{table} 
Table 5: Metabolic cost estimation following the 6 min walking test wearing non-powered EGO. compared to the non-powered EGO, the user's COT decreased by up to 24%, and the travel distance increased by up to 37%. These findings confirm that the proposed KAEGO system improves the walking energy efficiency in patients with incomplete paraplegia. The increase in the patient's HR is presumed to be due to the increase in the weight of the exoskeleton system and the limited freedom of the knee joint due to incomplete synchronization [10]. In addition, because the knee assist torque generates a large motion, a higher level of concentration is required to maintain gait balance, which could be the cause for the increase in the patient's HR. The study participant was a 40-year-old man who could walk with a non-powered EGO but was only able to train for less than 20 min per session due to muscle pain in the wrist and shoulder caused by the use of an elbow crutch. However, when using the KAEGO, he felt his dependence on the elbow crutch was reduced due to the knee motion assist, reducing the wrist and shoulder pain. This met the second hypothesis we proposed.