## 3 Results
### The Discomfort Index and Six Indices of NASA-TXL Rating Scales  
For the subjective performance, the two primary independent factors were still: (1) without-EXO and with-EXO carrying condition and (2) the four loading levels. The dependent experiment variables were: (1) the discomfort rating C and (2) the group weighted ratings of the NASA TLX scales (MD, PD, TD, OP, EF, FR). Because there were just nine investigated samples, the data abnormality was tested by boxplot. The Shapiro-Wilk method was used to test the data normality. A Levene variance homogeneity test was used. The results indicated that there were no abnormal data. The residual errors were normal (\(p>0.05\)).  
According to the literature [19], this experiment is a kind of Continuous SINGLE-axis MANUAL task. Considering the fact that the TLX index was developed for significantly more complex tasks, the  
\begin{table}
\begin{tabular}{c c c c} \hline \hline \multirow{2}{*}{**Muscles**} & **With- or Without-EXO** & **Load Level** & **W \(\times\) L** \\  & **(Main Effects)** & **(Main Effects)** & **(Interaction Effects)** \\  & **F (\(p\))** & **F (\(p\))** & **F (\(p\))** \\ \hline RF & **6.418 (\(p\) = 0.017)** & **26.124 (\(p\) = 0.000)** & **3.356 (\(p\) = 0.04)** \\ VM & 0.058 (\(p\) = 0.810) & **16.320 (\(p\) = 0.000)** & 0.734 (\(p\) = 0.427) \\ VL & **6.373 (\(p\) = 0.017)** & **19.836 (\(p\) = 0.000)** & 1.185 (\(p\) = 0.312) \\ BF & **22.653 (\(p\) = 0.000)** & 1.407 (\(p\) = 0.250) & 2.472 (\(p\) = 0.078) \\ ST & **12.637 (\(p\) = 0.001)** & **5.240 (\(p\) = 0.005)** & 2.767 (\(p\) = 0.062) \\ PL & **15.496 (\(p\) = 0.000)** & 6.728 (\(p\) = 0.005) & **4.158 (\(p\) = 0.031)** \\ GL & **21.391 (\(p\) = 0.000)** & **9.287 (\(p\) = 0.000)** & **6.729 (\(p\) = 0.003)** \\ \hline \hline \end{tabular}
\end{table}
Table 3: Summary of Two-Way ANOVA Results for the Main and Interaction Effects of With or Without and Load Final EMG Values. W \(\times\) L stands for with or without and load interaction. F means F test value. Lower-case \(p\) means statistical significance and the significant differences were bolded.  
Figure 9: With-Exo or without-Exo and four loading levels effects on initial values of normalized RMS (nRMS) for (**a**) the right knee extensors (RF, VM, VL); (**b**) for the right knee flexors (BF, ST); (**c**) the right plantar flexors (PL, GL). The star (*) indicates the significant difference (\(p<0.001\)) between two related factors.  
combined numeric value of the TLX is too coarse to be sensitive to the relatively small variations in the task elements. Therefore, the effect of \"with or without\" variation on the individual mean discomfort rating scales is shown in Figure 10a. Additionally, the individual mean MD, PD, TD, OP, EF, and FR rating scales are shown in Figure 10b. It is noticed that in the conventional load carriage, the workload demands for all effort required and the extended discomfort C for 0 kg level were defined as \"1\". With increasing load level, the subjective discomfort increased linearly and significantly in the conventional carriage, while in the exoskeleton assisted carriage condition, the discomfort increased much slower. Similar trends for the standard six rating scales could also be observed in Figure 10b.