# Evaluation of Standing-Up Motion from a Forward-Sloping Toilet Seat for Older People
## 2 Materials and Methods
### Data Analysis  
For this study, the time interval for the analysis of the standing-up motion started when the acromion marker moved forward and ended when the iliac crest marker stopped moving. The locus of the 3D body motion capture system was used to calculate the ankle dorsiflexion angle, which was defined as the angle between the head of the fibula, lateral malleolus, and floor in the sagittal plane. Before the standing-up motion, the motion capture system was also used to calculate the forward trunk inclination angle when the participant's buttocks were barely touching the toilet seat. The minimum angle between theacromion, iliac crest, and caput fibulae in the sagittal plane during the standing-up motion was defined as the forward trunk inclination angle. To compare the effect of the toilet seat angle on head motion, we focused on peak-to-peak displacement of the head in the sagittal plane. The peak-to-peak displacement of the head for each participant was the ensemble average normalized by dividing each displacement value by the participant's body length, as measured before the experiments. Averaging was performed for all motions (Figure 2).  
The center of pressure (COP) was calculated based on foot pressure distribution. To compare the influence of toilet seat angle on participant motion, we focused on peak-to-peak COP displacement in the \(X\)-axis and \(Z\)-axis (Figure 1a).  
EMG signals were passed through a high-pass filter using zero-phase-lag finite impulse response (FIR) with a 60 Hz cutoff frequency before analysis. To compare the rate of change, each participant's EMG signal ensemble average was normalized as follows: (a) the average EMG signal amplitude was calculated for each toilet seat angle (\(5^{\circ}\), \(10^{\circ}\), and \(15^{\circ}\)) and (b) the mean of the participant ensemble averages was taken. The signals were then rectified to obtain the root-mean-square (RMS) value of the muscle activity signal during the standing-up motion.  
For the objective data, differences by age group and toilet seat angle were determined using two-way analysis of variance (ANOVA) with Bonferroni test. Each participant's average normalized RMS EMG value for each of the four muscles was used. Average COP displacement and body motion were also calculated for each participant.  
For subjective data, differences according to age group were determined using the one-way non-parametric ANOVA. The Kruskal-Wallis test was used to compared scores for ease of the standing-up motion and overall score of the standing-up motion for each angle relative to a toilet seat angle of \(0^{\circ}\). The Bonferroni and Kruskal-Wallis tests were used to calculate the statistical significance at the 0.01 and 0.05 levels for multiple comparisons performed in this study. The Statistical Product and Service Solutions (SPSS) software package (IBM, SPSS Statistics version 24, Armonk, NY, USA) was used for statistical analyses.  
Figure 3 shows an example of raw data of the standing-up motion among older participants with a toilet seat angle of \(5^{\circ}\).  
Figure 2: Details of ankle dorsiflexion angle, forward trunk inclination angle, and peak-to-peak displacement of the head (\(X\) and \(Y\)-axes) in the sagittal plane.