## 4 Discussion
\begin{table}
\begin{tabular}{c c c c c} \hline \hline  & & **Min. Angle** & **Max. Angle** & **RoM** \\ \hline \multirow{3}{*}{Hip} & Ground walking & \(-\)14.56 \(\pm\) 7.50 & 54.40 \(\pm\) 12.59 & 68.97 \(\pm\) 14.65 \\  & Passive & 24.02 \(\pm\) 3.16 & 43.32 \(\pm\) 5.74 & 19.31 \(\pm\) 3.11 \\  & Motor active & 0.70 \(\pm\) 3.31 & 33.10 \(\pm\) 4.73 & 32.40 \(\pm\) 3.64 \\ \hline \multirow{3}{*}{Knee} & Ground walking & 13.85 \(\pm\) 6.66 & 93.81 \(\pm\) 14.31 & 79.96 \(\pm\) 19.25 \\  & Passive & 60.17 \(\pm\) 3.41 & 102.78 \(\pm\) 6.90 & 42.61 \(\pm\) 4.25 \\ \cline{1-1}  & Motor active & 3.06 \(\pm\) 1.40 & 50.71 \(\pm\) 7.80 & 47.65 \(\pm\) 7.35 \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Differences of lower limb angle according to gait conditions. In the result of the gait event parameter, the swing and stance phase ratios averaged at 68.8% and 31%, respectively--a ratio of approximately 7 to 3. This is the opposite result from the MGTR, where the ratio of swing and stance during normal walking is 4 to 6. It was confirmed that stance and stance times were twice as large as the swing time. Although the stance time was similar to normal walking, it is necessary to adjust the assist speed in the swing section more quickly because the gait was performed under the condition of 100% robot power assist. When the speed of the swing section increases, the event ratio of the stance is also expected to increase [25]. Alternatively, it is necessary to modify the gait trajectory at the ankle to increase the length of the device driving trajectory in the stance phase from heel strike to toe-off, or to reduce the swing phase from toe-off to heel strike [6; 26]. As such, it is necessary to modify the device to implement a gait event similar to a normal gait. The limitations of this study are as follows. First, in this experiment, the movement of the joints according to the initial step length and speed was confirmed, but additional experiments are needed to automatically adjust the step length according to the walking speed. This function can implement the characteristics of ground walking in which the step length increases when the walking speed increases. Second, the experiment was performed on normal subjects. The final target of user such as stroke and Parkinson's patients were not considered. In addition, the age of the patients was not considered. In general, patients with gait impairment are older. This study was conducted on normal young subjects in a small group. Since the this MGTR is in the preliminary development stage, it is considered that safety problems may occur when a patient with gait movement disorder actually boards. In a future study, we will measure the gait in the advanced MGTR, which is more concerned with safety issues when boarding for stroke and Parkinson's patients. Third, the optical camera system was used instead of the IMU system, which is a simplified gait measurement method used in the patient motion capture device. IMU system can calculate angles, velocity, and angular acceleration of each joint [27]. In a future study, we plan to conduct gait measurement and analysis using IMU system for patients with actual gait impairment. Fourth is that the effectiveness was not confirmed when rehabilitation in this VR-MGTR. It is necessary to conduct an intervention study on actual patients to conduct a comparative study of the training effect between the gait speed biofeedback with VR and MGTR systems, which is the R&D product, and the existing MGTR and VR with MGTR. This will be investigated in future research. In this system, the VR system was linked with MGTR according to the control of speed and step length when walking, and it is possible to implement it similar to the real world using a simulator. It is possible to develop and apply various programs, as well as a training program for this system, walking on a playground track. The advantages of VR are that it can provide feedback necessary for learning, motivating, and implementing actual body functional states [28].