# Evaluation of Standing-Up Motion from a Forward-Sloping Toilet Seat for Older People
## 4 Discussion  
### Effect of Toilet Seat Angle on the Standing-Up Motion  
Previously, the standing-up motion was evaluated based on objective data, such as EMG, 3D body motion, and COP, to support the analysis of physical loads (for reference, see [7]). Other studies have measured the effect of forward trunk inclination angle during the standing-up motion, but the ease of the motion was not measured [8,9]. In this study, both objective data (muscle activity, body motion, and COP based on foot pressure distribution) and subjective data (perceived ease) associated with the standing-up motion after toilet use were evaluated. Based on the subjective data provided by the participants, younger participants found it easy and comfortable to stand when the seat angle was 5\({}^{\circ}\), while older participants indicated ease and comfort when it was 10\({}^{\circ}\) (Figure 6b). Objective EMG, COP, and 3D body motion analysis results varied across individuals and age groups. Taken together, these results show that the perceived ease of the standing-up motion cannot always be explained with objective data only. Furthermore, ankle dorsiflexion angle decreased and forward trunk inclination angle increased monotonically with seat angle for all participants. The relationship between ease of the standing-up motion and ankle dorsiflexion angle was also evaluated. It has been reported that decreasing the stress of the standing-up motion requires ankle dorsiflexion, meaning that a person could easily stand up from a sitting position if there was little ankle dorsiflexion involved [14]. In another previous study [15], the dependence of physical loads experienced during the standing-up motion on knee flexion and ankle dorsiflexion angles was measured using a height-adjustable chair. In that study, the physical load during the standing-up motion was affected by foot position (i.e., ankle dorsiflexion), but not the seat height. As shown in Figure 3, ankle dorsiflexion angle decreased with increases in toilet seat angle for all participants, even though the height of the rear part of the toilet seat changed vertically to increase the toilet seat angle. Therefore, ease of the standing-up motion was affected ankle dorsiflexion angle, not by the (partially) higher toilet seat. We suggest that ankle dorsiflexion angle can indeed affect the standing-up motion; hence, when ankle dorsiflexion angle decreased with the increase in toilet seat angle, participants found it easier to stand up from the seat. Ease of the standing-up movement depends on various characteristics such as body height, body weight, and leg length, not just the \begin{table}
\begin{tabular}{c c c c} \hline \hline  & \multicolumn{3}{c}{**Toilet Seat Angle**} \\ \hline  & 5\({}^{\circ}\) & **10\({}^{\circ}\)** & **15\({}^{\circ}\)** \\ \hline \multicolumn{4}{c}{Objective data} \\ \hline Motion & Ankle dorsiflexion angle & & \\  & Forward trunk inclination angle & & * \\  & Forward–backward head motion & ** & ** & ** \\  & Up–down head motion & ** & ** & ** \\ COP & Peak-to-peak displacement in the \(X\)-axis & & & ** \\  & Peak-to-peak displacement in the \(Z\)-axis & * & & * \\ EMG & Electro spine & ** & & \\  & Rectus femoris & & & \\  & Tibialis anterior & ** & & \\  & Gastrocnemius & & & \\ \hline \multicolumn{4}{c}{Subjective data} \\ \hline Score & Ease score & & & \\  & Overall score & & & \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Summary of the quantitative performance of statistically significant differences between age groups ((**) \(p<0.01\) and (*) \(p<0.05\), respectively). difference in ankle dorsiflexion angle. In future work, we plan to determine the ease of the standing-up movement in terms of the contribution of various factors such as EMG, COP, and body motion, and discuss the individual characteristics of the standing-up motion. There is a clear need to evaluate the ease of the standing-up motion not only with measured objective data, but also with subjective data.