# Biomechanical Effects on Lower Extremities in Human-Robot Collaborative Agricultural Tasks
## 4 Discussion  
The findings of the post hoc analysis demonstrated some statistically important differences among deposit heights, the main ones of which are depicted in the form of bar charts in Figure 4 (kinetic and kinematic variables) and Figure 5 (EMG data). It can be deduced that when the case of 90 cm was considered, the participants tended to bend their knees more compared to the other lower heights (Figure 4c). As revealed by the results of [PERSON] et al. [19], who investigated the biomechanical differences between novice and experienced workers, this can be attributed to the fact that greater knee bending can bring the worker closer to the object. This is a well-known technique for decreasing the moment at the L5/S1 spinal segment [68; 69]. Hence, in contrast with novice workers, the experienced ones kneel more with the intention of avoiding possible discomfort in the lumbar region. This finding reinforces our initial assumption that specific attention must be paid to the experience of participants in such kinds of experimental measurements. \begin{table}
\begin{tabular}{c c c c c} \hline \hline \multirow{2}{*}{**Variables**} & \multicolumn{3}{c}{**Height**} & \multirow{2}{*}{\(p\)} \\ \cline{2-2} \cline{4-4}  & **70 cm** & **80 cm** & **90 cm** & \\ \hline Mean EMG VM (Phase 1) & 100 \(\pm\) 0 & 114.60 \(\pm\) 28.61 & 116.76 \(\pm\) 22.41 & \textless{}0.05 \\ Peak EMG VM (Phase 1) & 100 \(\pm\) 0 & 130.14 \(\pm\) 42.82 & 126.49 \(\pm\) 36.37 & \textless{}0.05 \\ Mean EMG VM (Phase 2) & 100 \(\pm\) 0 & 109.11 \(\pm\) 36.26 & 99.46 \(\pm\) 28.44 & NS \\ Peak EMG VM (Phase 2) & 100 \(\pm\) 0 & 122.61 \(\pm\) 27.63 & 111.98 \(\pm\) 26.99 & NS \\ Mean EMG VM (Phase 3) & 100 \(\pm\) 0 & 97.01 \(\pm\) 25.11 & 107.06 \(\pm\) 35.99 & NS \\ Peak EMG VM (Phase 3) & 100 \(\pm\) 0 & 86.85 \(\pm\) 37.29 & 115.96 \(\pm\) 63.73 & NS \\ Mean EMG ES (Phase 1) & 100 \(\pm\) 0 & 98.43 \(\pm\) 17.34 & 113.94 \(\pm\) 23.35 & NS \\ Peak EMG ES (Phase 1) & 100 \(\pm\) 0 & 118.04 \(\pm\) 39.98 & 122.03 \(\pm\) 30.31 & \textless{}0.05 \\ Mean EMG ES (Phase 2) & 100 \(\pm\) 0 & 104.10 \(\pm\) 22.11 & 113.31 \(\pm\) 24.35 & NS \\ Peak EMG ES (Phase 2) & 100 \(\pm\) 0 & 97.52 \(\pm\) 20.91 & 104.75 \(\pm\) 19.66 & NS \\ Mean EMG ES (Phase 3) & 100 \(\pm\) 0 & 99.20 \(\pm\) 22.96 & 102.66 \(\pm\) 24.07 & NS \\ Peak EMG ES (Phase 3) & 100 \(\pm\) 0 & 101.59 \(\pm\) 33.57 & 107.84 \(\pm\) 34.97 & NS \\ Mean EMG GASTRO (Phase 2) & 100 \(\pm\) 0 & 134.48 \(\pm\) 63.20 & 120.52 \(\pm\) 79.51 & NS \\ Peak EMG GASTRO (Phase 2) & 100 \(\pm\) 0 & 143.11 \(\pm\) 95.06 & 149.10 \(\pm\) 197.03 & NS \\ Mean EMG GASTRO (Phase 3) & 100 \(\pm\) 0 & 111.37 \(\pm\) 36.05 & 104.60 \(\pm\) 31.10 & NS \\ Peak EMG GASTRO (Phase 3) & 100 \(\pm\) 0 & 114.00 \(\pm\) 39.83 & 106.74 \(\pm\) 21.09 & NS \\ Mean EMG BF (Phase 2) & 100 \(\pm\) 0 & 115.22 \(\pm\) 40.03 & 99.67 \(\pm\) 30.77 & NS \\ Peak EMG BF (Phase 2) & 100 \(\pm\) 0 & 127.06 \(\pm\) 65.50 & 109.12 \(\pm\) 44.57 & NS \\ Mean EMG BF (Phase 3) & 100 \(\pm\) 0 & 100.93 \(\pm\) 25.54 & 94.50 \(\pm\) 24.11 & NS \\ Peak EMG BF (Phase 3) & 100 \(\pm\) 0 & 91.60 \(\pm\) 36.09 & 89.70 \(\pm\) 31.13 & NS \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Peak and mean normalized RMS EMG values during the three phases of the symmetric lifting task for heights 70, 80, and 90 cm; data are reported as mean \(\pm\) standard deviation. Figure 4: Bar charts showing the mean values (\(\pm\) standard deviation) of the statistically important alterations: (**a**) Maximum knee extension moment, (**b**) maximum hip extension moment, and (**c**) maximum knee flexion angle for the three different deposit heights along with the standard deviation. The larger knee flexion at the higher deposit heights was accompanied, as expected, by simultaneous larger activation of VM during phase 1 (Figure 5a,b). This has also been reported by other studies like [70], who examined the squat exercise. More specifically, the muscles contract eccentrically during this phase.