## 3 Results
### Muscular Demands  
Overall, the muscle demands in both the back and leg muscles were the lowest during the bending portion, while both the retraction and transitioning from bending to retraction imposed higher demands. Specifically, the demands were \(\sim\)28%, 10%, \(\sim\)93%, and 62% higher in the LES, RES, LBF, and RBF muscles (\(p<0.01\)) during the transition vs. bending portion, respectively (Table 1). Over time, an increase in activity was seen in the LES, RES, and RBF muscles for all three portions, and in the LBF during the transition portion  
Figure 3: Schematic showing segmentation of each bending and retraction cycle from the upper-back marker during 30 cycles of a repetitive trunk flexion–extension task based on type of spatial activity categorized as bending, retraction, or transition movement (Adapted from [31]).  
(Table 2). Across the postures, the RES activity during retraction was the highest (0.68 (0.3)) during the asymmetric postures and was greater than the symmetric postures by \(\sim\)19% (Table 3).  
Considering all three task portions, the benefits of the BSIE for back muscles were minimal (0-1.8%), with no effects on the RES, while the benefits were more prominent in the leg muscles (10-18%), specifically the LBF and RBF (Table 4). Specifically, the muscle demands were greater when the BSIE was worn during the retraction portion. The RES and LES activities were \(\sim\)4.8% and 3.6% higher, respectively, with the BSIE during the retraction portion (Figure 4). Meanwhile, most benefits were observed in the LBF and RBF muscles, with \(\sim\)23% and \(\sim\)17% lower activity during retraction with the BSIE. Variations in the muscle demands across the assistance, time, and posture factors are depicted in Figures 4-6 and are described separately in the following sections across the three task portions.  
\begin{table}
\begin{tabular}{c c c c c c c c c} \hline \hline  & \multicolumn{2}{c}{LES} & \multicolumn{2}{c}{RES} & \multicolumn{2}{c}{LBF} & \multicolumn{2}{c}{RBF} \\ \hline
**Portion** & **Mean** & **SD** & **Mean** & **SD** & **Mean** & **SD** & **Mean** & **SD** \\ \hline BD & 0.45 & 0.17 & 0.48 & 0.21 & 0.14 & 0.11 & 0.14 & 0.10 \\ RT & 0.57 & 0.20 & 0.62 & 0.27 & 0.27 & 0.18 & 0.27 & 0.18 \\ TS & 0.60 & 0.18 & 0.54 & 0.27 & 0.39 & 0.18 & 0.27 & 0.18 \\ \hline \hline \end{tabular}
\end{table}
Table 1: Overall variations in muscle demands across the bending (BD), retraction (RT), and transition (TS) portions of the repetitive-bending task.  
\begin{table}
\begin{tabular}{c c c c c c c c c c} \hline \hline  & \multicolumn{2}{c}{**LES**} & \multicolumn{2}{c}{**RES**} & \multicolumn{2}{c}{**LBF**} & \multicolumn{2}{c}{**RBF**} \\ \hline
**Portion** & **Time** & **Mean** & **SD** & **Mean** & **SD** & **Mean** & **SD** & **Mean** & **SD** \\ \hline BD & 0.42 & 0.16 & 0.46 & 0.19 & 0.14 & 0.12 & 0.14 & 0.09 \\ ED & 0.47 & 0.18 & 0.51 & 0.21 & 0.  
\begin{table}
\begin{tabular}{c c c c c c c c c} \hline \hline  & \multicolumn{2}{c}{**LES**} & \multicolumn{2}{c}{**RES**} & \multicolumn{2}{c}{**LBF**} & \multicolumn{2}{c}{**RBF**} \\ \cline{2-9}  & **Mean** & **SD** & **Mean** & **SD** & **Mean** & **SD** & **Mean** & **SD** \\ \hline E & 0.53 & 0.21 & 0.55 & 0.25 & 0.25 & 0.18 & 0.21 & 0.16 \\ N & 0.54 & 0.18 & 0.55 & 0.26 & 0.28 & 0.20 & 0.25 & 0.17 \\ \hline \hline \end{tabular}
\end{table}
Table 4: Muscle demands with (E)/without (N) assistance from BSIE, averaged over bending, retraction, and transition portions.  
Figure 4: Graph showing muscle demands in left/right erector spinase (LES/RES) and left/right bicep femoris muscles compared between without assistance (N) and with assistance (E) and categorized according to task portion as bending (BD), retraction (RT), and transition (TS) (Note: lack of statistical significance between E and N conditions is shown by “NS”).