## 3 Results  
Table 3 shows the RMSE comparison between the angles extracted from the RGB-MAS and the ones extracted by the Vicon system for a pure system-to-system analysis. \begin{table}
\begin{tabular}{c c} \hline \hline
**Pairs of Angles Compared between the Two Systems.** \\ \hline
**Vicon** & **RGB-MAS** \\ \hline Average between L and R neck flexion/extension & Neck flexion/extension \\ L/R shoulder abduction/adduction Y component & L/R shoulder abduction \\ L/R shoulder abduction/adduction X component & L/R shoulder flexion/extension \\ L/R elbow flexion/extension & L/R elbow flexion/extension \\ Average between L and R spine flexion/extension & Trunk flexion/extension \\ L/R knee flexion/extension & L/R knee bending angle \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Pairs of angles that have been compared between Vicon and RGB systems. \begin{table}
\begin{tabular}{c c c c} \hline \hline  & \multicolumn{3}{c}{**RMSE RGB-MAS vs. Vicon [\({}^{\circ}\)]**} \\ \cline{2-4}  & **T-Pose** & **Seated** & **Standing Relaxed** & **Reach** \\ \hline Neck flexion/extension & 6.83 & 16.47 & 19.21 & 9.58 \\ Left shoulder abduction & 12.66 & 45.16 & 13.07 & 45.46 \\ Right shoulder abduction & 11.64 & 50.66 & 7.93 & 43.23 \\ Left shoulder flexion/extension & 27.86 & 57.19 & 21.53 & 71.29 \\ Right shoulder flexion/extension & 33.73 & 52.90 & 57.88 & 82.93 \\ Left elbow flexion/extension & 7.13 & 16.90 & 21.15 & 27.05 \\ Right elbow flexion/extension & 5.46 & 13.19 & 22.11 & 53.30 \\ Trunk flexion/extension & 0.35 & 8.61 & 0.91 & 2.95 \\ Left knee flexion/extension & 2.39 & 46.25 & 7.38 & 24.76 \\ Right knee flexion/extention & 0.21 & 4.79 & 0.07 & 0.12 \\ \hline \hline \end{tabular}
\end{table} 
Table 3: RMSE values obtained comparing RGB-MAS angles with the Vicon ones. As it can be observed, angle predictions provided by the proposed system result in general lower accuracy, in the case of shoulder abduction and shoulder and elbow flexion/extension. The accuracy is particularly low if we consider the reach posture. This is probably because of perspective distortions. However, the pickup posture could not be traced with the Vicon system, due to occlusion problems caused by the presence of the box that occludes some of the markers needed by it. Table 4 allows easy comparison of the RMSE between angles respectively predicted by the RGB-MAS and the Vicon system, and those manually measured. These results suggest that the proposed system can be considered somehow feasible to support ergonomists doing their analysis. Figure 6 highlights the similarities and discrepancies between the angle predictions provided by RGB-MAS and Vicon system with respect to the manual analysis. It can be observed that the prediction provided by the RGB-MAS suffers from a wider variability compared to the reference system. As for the neck flexion/extension angle, the RGB-MAS system slightly overestimates the results compared to the Vicon system. This occurs more pronouncedly for the shoulder abduction and flexion/extension as well, especially when abduction and flexion both occur simultaneously. In Figure 7, the keypoint's locations and the skeleton are shown superimposed over the posture pictures. In particular, from the picture of the Pick Up posture, we can see that the small occlusion that caused problems to the Vicon system did not cause any consequences to the RGB-MAS system. Moreover, high variability is also found for all the angles of the left-hand side of the body. Nevertheless, RGB-MAS accurately predicts the trunk flexion/extension and the right-hand side angles. This left-right inconsistency can be due to the lack of a left camera, and so the left-hand side angles are predicted with less confidence than their right-hand side counterparts.