## 4 Discussion  
Regular load carriage often happens in specific situations, such as for soldiers, school children, hikers, and assembly line workers. It was one of the most frequent risk factors for MSDs which have been confirmed by EU-OSHA. Although a few exoskeletons have been developed to decrease the loading effects on the human body, there is still lacking evidence that these assistive devices allow human beings to move or walk freely or make carriage-loaded MSDs decrease. In this study, one exoskeleton prototype was examined as a potential ergonomic device for application \begin{table}
\begin{tabular}{c c c c} \hline \hline
**NASA-TLX Rating** & \begin{tabular}{c} **With- or Without-EXO** \\ **(Main Effects)** \\ **F (\(p\))** \\ \end{tabular} & \
\begin{tabular}{c} **Load Levels (L)** \\ **(Main Effects)** \\ **F (\(p\))** \\ \end{tabular} &
\begin{tabular}{c} **\(W\times L\)** \\ **(Interaction Effects)** \\ **F (\(p\))** \\ \end{tabular} \\ \hline Discomfort & 32.177 (\(<\)0.0001) & 5.764 (\(<\)0.05) & 1.288 (\(=\)0.292) \\ Mental Demand & 14.513 (\(<\)0.0001) & 4.030 (\(<\)0.05) & 0.570 (\(=\)0.638) \\ Physical Demand & 20.006 (\(<\)0.0001) & 15.008(\(<\)0.0001) & 1.564 (\(=\)0.213) \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Summary of Two-Way ANOVA Results for the Main and Interaction Effects on the Discomfort, Mental Demand and Physical Demand. (**Note:** The significant differences were indicated as bold and italic style. F means F test value. Lower-case \(p\) indicates statistical significance.) Figure 11: The comparison of weight factors between without-exo and with-exo walking conditions. Figure 12: The interaction trend plot of with-Exo or without-Exo \(\times\) load level. in regular loading tasks. Some advices should be provided to improve the ergonomic performance and human-robot interaction performance so as to decrease carriage-loaded MSDs. A few assistive exoskeletons for the lower extremities are already commercially available. Some have been introduced into rehabilitation centers, industry assembly lines, and military training [20; 21; 22]. Some measures and analyses on the metabolic effects, muscle activities, and human gait patterns have been carried out on the related exoskeletons [11; 23; 24]. This study remains one of the first to quantify muscle activities for which the exoskeletons are not specifically designed to decrease the metabolic cost. In particular, this investigation aims to quantify muscle amplitude and activities that result from performing four levels of load carriage walking on a treadmill, with and without an exoskeleton. At the same time, this study examined the subjective performance of the exoskeleton using the extended NASA-TLX questionnaire. Most research has examined muscle activities of the lower limb, comparing the mean and peak amplitude from free treadmill walking to exoskeleton treadmill walking, and have reported a significant increase in muscle activity with the exoskeleton [24]. Few studies have reported decreased muscle activity when using an exoskeleton [25]. It is important to note that the existing augmenting exoskeletons have reported no decrease in muscle activity and oxygen consumption [11; 20]. However, this is not to say the assistive exoskeletons pose no use to human beings. It is reported that any real metabolic advantage imparted by the EXO may be dependent on the magnitude of the load carried, such that the metabolic energy cost per unit of mass becomes lower than non-EXO assisted load carriage only when heavy loads (greater than 50% of body mass) are carried by the device [11]. The results of this study are consistence with the former mentioned results. As shown in Figure 9, the interaction of the Load level \(\times\) with or without-EXO should happen with increasing of load level. When comparing the load level main effects on muscle activity, it is illustrated that the structure of the effects are different for the with- and without-Exo walking conditions.