# Verification of Industrial Worker Walking Efficiency with Wearable Hip Exoskeleton
## 4 Discussion
### Treadmill Walking  
There was no significant difference in the average muscle activity between the WIM and no WIM groups of treadmill walking. When wearing a WIM, the average muscle activity of the thigh (RF and ST) decreased, and the average muscle activity of the shank (TA and GCM) slightly increased, but the difference was not statistically significant. In addition, there was no significant difference in RF, ST, and TA muscle fatigue between the two conditions; however, when wearing a WIM, muscle fatigue in the activity of the GCM decreased by 79.5%, which was confirmed to be a statistically significant decrease. The muscle fatigue value presented in this study was an analysis of the slope of the frequency that occurred in the entire measurement section; if the measured value was negative, it was interpreted that muscle fatigue had occurred. Fatigue was found to occur in all muscles when walking on a treadmill, regardless of whether a WIM was worn. Fatigue in the RF, ST, and GCM muscles, but not the TA, was found to be reduced when wearing WIM. Meanwhile, in this study, TA muscle fatigue was found to increase by 18.3%, although this increase was not statistically significant. The WIM assists the flexion of the hip joint at the front of the pelvis, thereby assisting the forward movement of the leg. These features can increase the range of flexion of the lower-extremity joints, especially the hip joint. [PERSON] et al. (2017) reported that, when wearing a soft robot suit that provided hip flexion assistance by wrapping a belt, the maximum hip flexion angle increased by an average of 5.4%, and the maximum vertical positions of the knee and ankle joints also increased [7]. Although the lower-extremity angles were not directly measured in this study, considering previous studies, it is expected that the hip, knee, and ankle joint angles would have increased even if a WIM with a similar control method had been used. In the case of assistive exoskeletons that assist in bending the legs, the overall angle of the lower-extremity joints may increase if too strong torque is applied. Excessive deviation of the lower-extremity joint angles from the normal range can result in inappropriate muscle activity patterns, ultimately leading to increased muscle fatigue. \begin{table}
\begin{tabular}{c c c c c} \hline \hline  & **No** & **WIM** & **\%** & **t-Value** \\ \hline Performance time (sec) & 98.00 \(\pm\) 16.21 \(\lx@math@degree\) & 109.10 \(\pm\) 19.43 & 11.33\% & \(-\)1.941 \\ \hline Oxygen uptake & 15.73 \(\pm\) 2.74 & 13.53 \(\pm\) 1.86 & \(-\)13.99\% & 3.116 \({}^{*}\) \\ \hline Heart rate (ppm) & 114.62 \(\pm\) 15.01 & 105.60 \(\pm\) 12.98 & \(-\)7.87\% & 3.329 \({}^{**}\) \\ \hline Energy expenditure per minute (kcal/min) & 5.94 \(\pm\) 0.89 & 5.17 \(\pm\) 0.89 & \(-\)12.91\% & 3.369 \({}^{**}\) \\ \hline Total energy expenditure (kcal) & 9.59 \(\pm\) 1.50 & 9.43 \(\pm\) 2.09 & \(-\)1.59\% & 0.320 \\ \hline Net EEM & 4.89 \(\pm\) 0.88 & 4.12 \(\pm\) 0.87 & \(-\)15.65\% & 3.369 \({}^{**}\) \\ \hline EE, energy expenditure; \(\lx@math@degree\) mean \(\pm\) standard deviation; \({}^{*}\)\(p\) < 0.05; \({}^{**}\)\(p\) < 0.01. & & \\ \end{tabular}
\end{table} 
Table 5: Results of energy expenditure during walking up stairs. Therefore, it is necessary to supplement the control mechanism to assist the legs through appropriate torque control, while preventing excessive leg elevation. Additionally, the main outcome related to gait efficiency in this study was a reduction in muscle fatigue in the GCM. In the case of the GCM, there was no difference in muscle activity between the WIM and no-WIM groups, but muscle fatigue was significantly reduced. When muscle contraction increases, muscle activity also tends to increase; however, increased muscle activity does not necessarily increase muscle fatigue. The patterns of muscle activity and fatigue may vary depending on the action and type of muscle [31]. Muscle fatigue refers to a decrease in the ability of a muscle to generate maximum force.