## 3 Results  
The differences in the stance durations between the two devices are summarized in Table 1. The mean differences of the stance durations for all of the participants were within \(-17\) to \(10\) ms while straight walking, and between \(-16\) and \(24\) ms and \(-19\) and \(11\) ms while walking along a curved path in each direction (CW and CCW, respectively). To measure the accuracy of the vGRF, Pearson's correlation coefficient (Table 2) and %RMSE (Table 3) values were calculated, and they revealed agreement between the two devices (\(r\) > 0.96 and %RMSE < 6.1% in the mean values). The plots of the vGRF, as measured from the two devices in a stance closest to the mean %RMSE value, are shown in Figure 3.  
\begin{table} \begin{tabular}{c c c c c c c} \hline \hline \multirow{2}{*}{**Subject**} & \multicolumn{2}{c}{**Straight Walking (ms)**} & \multicolumn{4}{c}{**Curved Walking (ms)**} \\ \cline{2-7}  & \multicolumn{2}{c}{**CW**} & \multicolumn{2}{c}{**CCW**} \\ \cline{2-7}  & **LF** & **RF** & **LF (OUT)** & **RF (IN)** & **LF (IN)** & **RF (OUT)** \\ \hline A & 4.7 (\(\pm\)8.8) & \(-4.1\) (\(\pm\)7.9) & 4.5 (\(\pm\)6.3) & 0.0 (\(\pm\)8.1) & \(-7.5\) (\(\pm\)6.6) & \(-9.9\) (\(\pm\)8.3) \\ B & 9.6 (\(\pm\)7.3) & 8.8 (\(\pm\)8.2) & \(-16.0\) (\(\pm\)7.9) & \(-14.2\) (\(\pm\)4.4) & \(-1.9\) (\(\pm\)6.9) & 0.0 (\(\pm\)6.2) \\ C & 3.5 (\(\pm\)5.3) & \(-1.2\) (\(\pm\)4.4) & 7.5 (\(\pm\)6.2) & \(-0.7\) (\(\pm\)6.2) & \(-10.1\) (\(\pm\)4.1) & \(-18.3\) (\(\pm\)7.6) \\ \hline \hline \end{tabular} 
\begin{tabular}{c c c c c c c} \hline \hline \multirow{2}{*}{**Subject**} & \multicolumn{2}{c}{**Straight Walking (\%)**} & \multicolumn{4}{c}{**Curved Walking (\%)**} \\ \cline{2-7}  & **LF** & **RF** & **LF (OUT)** & **RF (IN)** & **LF (IN)** & **RF (OUT)** \\ \hline A & 2.7 (\(\pm\)0.6) & 2.5 (\(\pm\)0.6) & 3.9 (\(\pm\)1.5) & 2.4 (\(\pm\)0.8) & 3.1 (\(\  
BAPs of the data from all the tasks for one participant are shown in Figure 4. These results showed no clear relationship between the difference and the mean for the vGRF while walking. The results showed that a few samples measuring small forces had large differences in the vGRF between the two devices, particularly in the straight walking. The mean (\(\pm\) standard deviations) of the RMSEs of the COP trajectory in the \(x\) and \(y\) directions are summarized for each task in Tables 4-6. The results showed that the RMSEs were within 8 to 24 mm in the \(x\) direction and 4 to 7 mm in the \(y\) direction while walking straight, within 9 to 19 mm in the \(x\) direction and 5 to 9 mm in the \(y\) direction while walking CW along the curved path, and within 6 to 12 mm in the \(x\) direction and 6 to 18 mm in the \(y\) direction while walking CCW along the curved path. The COP trajectories from the two devices in a step with the RMSE value closest to the mean are plotted for each walking task in Figure 5.  
Figure 4: Bland–Altman plots showing the comparison between the force plates and the Nintendo Wii Balance Board (WBB). (**a**) Data from 10 steps walking straight (right foot—RF). (**b**) Data from 10 steps walking clockwise (CW) along the curved path (RF (IN—inside foot turning)). Figure 3: Vertical ground reaction force (vGRF) measured from the Nintendo Wii Balance Board (WBB) and the force plate in a stance while (**a**) walking straight (right foot—RF), and (**b**) walking along a curved path in a clockwise (CW) direction (RF (IN—inside foot turning)). \begin{table}
\begin{tabular}{c c c c c} \hline \hline \multirow{2}{*}{**Subject**} & \multicolumn{2}{c}{**LF (IN)**} & \multicolumn{2}{c}{**RF (OUT)**} \\ \cline{2-5}  & \(x\) **(mm)** & \(y\) **(mm)** & \(x\) **(mm)** & \(y\) **(mm)** \\ \hline A & 17.6 (\(\pm\)4.5) & 7.6 (\(\pm\)1.0) & 6.9 (\(\pm\)1.7) & 7.5 (\(\pm\)1.4) \\ B & 15.1 (\(\pm\)6.4) & 10.1 (\(\pm\)3.5) & 7.3 (\(\pm\)1.5) & 6.0 (\(\pm\)1.1) \\ C & 15.0 (\(\pm\)2.2) & 8.1 (\(\pm\)1.3) & 10.4 (\(\pm\)3.7) & 8.3 (\(\pm\)1.2) \\ \hline \hline \end{tabular}
\end{table}