# Validation of a Horizontally Dynamic Armrest for Joystick Controlled Mobile Equipment
## 4 Discussion  
Results for iEMG and pEMG were largely in agreement with [PERSON] et al. [14] with the exception of the high activity of the AD during inward movements, which participants may have used to assist with medial rotation of the arm [35]. The dynamic armrest increased or did not significantly change muscle activation in the BB, ECR, FCR, TRI, and UT when compared with the static armrest. The DA did not significantly reduce activation in the ECR and FCR compared to the SA and NA during inward and outward motions. Interestingly, the NA decreased activation of the AD and ECR during inward movements, and decreased activation of the FCR during outward movements when compared to the SA. In addition, the DA increased activation of the FCR during fore movements, as well as the activation of the PD and TRI during aft and inward movements when compared to the SA. Fore-aft dynamic armrests were shown to reduce activation in the UT [1,27], PD, and AD [27]; however, these reductions in activation were not observed with the addition of a horizontally dynamic armrest on top of a pendulating fore-aft dynamic armrest. The success of the DA was determined on the basis of whether it reduced muscle activation in the eight muscles tested, especially the FCR and ECR muscles in comparison to \begin{table}
\begin{tabular}{c c c} \hline \hline
**Armrest** & **Direction** & **Force (N)** \\ \hline DA & F & 27.3 \(\pm\) 10.1 \\ SA & F & 28.4 \(\pm\) 9.8 \\ NA & F & 28.5 \(\pm\) 6.26 \\ \hline DA & A & 7.5 \(\pm\) 7.1 \\ SA & A & 9.7 \(\pm\) 10.0 \\ NA & A & 12.4 \(\pm\) 10.3 \\ \hline DA & I & 12.1 \(\pm\) 12.7 \\ SA & I & 12.6 \(\pm\) 13.7 \\ NA & I & 12.6 \(\pm\) 14.7 \\ \hline DA & O & 30.5 \(\pm\) 10.3 \\ SA & O & 30.8 \(\pm\) 10.3 \\ NA & O & 30.3 \(\pm\) 9.8 \\ \hline \hline \end{tabular}
\end{table} 
Table 6: Peak joystick input force data for each armrest condition and motion direction, expressed as mean \(\pm\) standard deviation (DA = dynamic armrest, SA = stationary armrest, and NA = no armrest) movement direction (F = fore, A = aft, I = inward, and O = outward). \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Variable** & \
\begin{tabular}{c} **Significant Differences** \\ **between Armrest** \\ **Conditions (Bonferroni)** \\ \end{tabular} & \(p\) & \(\eta_{p}\)\({}^{2}\) &
\begin{tabular}{c} **F-Value for Armrest** \\ **(ANOVA)** \\ \end{tabular} \\ \hline Perceived effort & DA \textless{} NA & 0.01 & 0.30 & F(2,24) = 5.11 \\ Perceived discomfort & DA \textless{} NA & 0.04 & 0.23 & F(2,24) = 3.59 \\ Overall effectiveness & DA \textgreater{} SA & 0.01 & 0.42 & F(1,12) = 8.87 \\ \hline \hline \end{tabular}
\end{table} 
Table 7: Summary of statistically significant main effects and interactions (\(p\) < 0.05) for the questionnaire results between armrests (DA = dynamic armrest, SA = stationary armrest, and NA = no armrest). \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Armrest** & **Perceived Effort** & **Perceived Discomfort** & **Overall Effectiveness** \\ \hline DA & 1.9 \(\pm\) 0.9 & 1.3 \(\pm\) 0.9 & 4.9 \(\pm\) 0.8 \\ SA & 2.4 \(\pm\) 1.3 & 2.3 \(\pm\) 1.9 & 3.5 \(\pm\) 1.5 \\ NA & 2.6 \(\pm\) 0.8 & 2.5 \(\pm\) 1.5 & – \\ \hline \hline \end{tabular}
\end{table} 
Table 8: Questionnaire data for each armrest condition (DA = dynamic armrest, SA = stationary armrest, and NA = no armrest), expressed as mean \(\pm\) standard deviation (perceived effort and discomfort: 0 = none, 6 = tremendous; overall effectiveness: 0 = not effective, 6 = effective). a SA and NA, as these are two of the most important muscles involved in inward-outward joystic manipulation [14]. The DA did not significantly reduce the activation of any muscle groups during inward and outward joystic movements when compared to the SA. Furthermore, decreased activation was observed in the PD (aft) and AD (inward) when using NA compared to DA. The only cases in which the DA significantly reduced muscle activation when compared to the SA was for the BB during fore movements and the PD during after movements.