## 4 Result and Discussion  
Wilcoxon Signed Rank test has been performed to calculate whether there were significant differences between data, particularly between the data collected among the four tasks and for the same task but in the two configurations: on the ground and the ladder. 24 out of 26 subjects were right-handed and only 2 were left-handed. Given the limited number of left-handed subjects, it was decided not to conduct the analyses separately as the results obtained would not have been statistically significant. Correlations and the strength of the relationship between the variables, particularly between the subjective data (perceived (dis)comfort, from questionnaires and CAMan) and objective ones (RULA) were calculated with IBM(r) (Armonk, NY, USA) SPSS(r) Statistics version 24. Spearman index was computed since data was not normally distributed. The data analysis had two specific purposes:  
The first target was to understand, for each task, if there was a significant difference between the task carried out from the ground and the ladder. This analysis was carried out both in terms of RULA score, in terms of discomfort (questionnaire) rating, and in terms of comfort (CAMan) rating. Since the operations involved an asymmetrical use of the body, the right and left sides were considered separately. The second target was to understand, for each task, which parts of the body were most in discomfort and whether there were correlations between the data acquired from the questionnaire and the results of the RULA and CAMan analysis. * Frontal screwing  
The RULA and CAMan analysis shows no significant differences, neither between the right and left side of the body nor between the tasks performed from the ground and on a ladder (score = 3-4, further investigations are needed) (Table 2). CAMan results show the lowest values for the wrist (very low comfort). Otherwise, the perceived discomfort is significantly higher when the task is carried out on the ladder. The reason lies in the discomfort perceived in the knee. RULA and CAMan do not consider the lower limbs and do not show significant differences between ground and ladder tasks. However, a significant difference emerges from the questionnaire in terms of global comfort. This confirms that the discriminating factor is the knees, assessed only in the questionnaire. Furthermore, the questionnaires show a higher average knee discomfort value for ladder work. Correlation analysis confirms this result. For the ladder operation, knee discomfort has a positive correlation with the overall discomfort (and a negative correlation with to participant height (Table 3). The difference in perceived discomfort between the ground and on the ladder, therefore, is due to the forced contact between the knees and the steps in order to facilitate the balance of the body during the execution of the task. For height, from the analysis of the videos it was noted that the taller the subject, the lower the area/time of contact between knees and parts of the ladder (steps). Furthermore, the cross-analysis shows strong negative correlations between the CAMan results and the questionnaire. As \begin{table}
\begin{tabular}{c c c c c c c c c c} \hline \hline \multirow{2}{*}{**Frontal Screwing**} & **RULA** & **RULA** & **Perceived** & **Effort** & **Left** & **Right** & **Wrist-Hand** & **CAMan** & **CAMan** \\  & **(Right)** & **(Left)** & **Discomfort** & **Needed** & **Knee** & **Knee** & **Evaluation** & **(Right)** & **(Left)** \\ \hline Mean (Ladder) & 4.57 & 3.29 & 4.05 & 1.32 & 1.18 & 1.18 & 2.45 & 7.08 & 7.15 \\ St. Dev. (Ladder) & 0.81 & 0.56 & 2.21 & 0.65 & 2.06 & 1.82 & 0.67 & 0.81 & 0.90 \\ Mean (Ground) & 4.38 & 3.24 & 2.73 & 1.18 & 0.05 & 0.09 & 2.05 & 7.59 & 8.11 \\ St. Dev. (Ground) & 0.59 & 0.54 & 2.05 & 0.50 & 0.21 & 0.43 & 0.79 & 0.78 & 0.90 \\ Mean Difference & 0.19 & 0.05 & 1.32 & 0.14 & 1.14 & 1.09 & 0.41 & 0.51 & 0.96 \\ Stochastic Significance & NO & NO & YES & NO & YES & YES & YES & YES \\ \hline \hline \end{tabular}
\end{table}