## 4 Discussion  
Here, we examined if changes in muscle synergies (e.g., number of synergies and muscle recruitment) could facilitate elucidation of how balance training interventions affect those at high fall risk (i.e., older adults that consider themselves overall healthy and those that have survived stroke). In order to direct goal-focused movements, such as overground walking, the central nervous system must map sensory inputs to motor output. Muscle synergies allow insights into how the muscles work together to execute a specific task. Here, \begin{table}
\begin{tabular}{c c c c c c c c c} \hline \hline \multirow{3}{*}{**VAF**} & \multicolumn{6}{c}{**Walking Condition**} \\ \cline{2-9}  & \multicolumn{2}{c}{**FW**} & \multicolumn{2}{c}{**BW**} & \multicolumn{2}{c}{**FT-W**} & \multicolumn{2}{c}{**BT-W**} \\ \cline{2-9}  & **Pre** & **Post** & **Pre** & **Post** & **Pre** & **Post** & **Pre** & **Post** \\ \hline
80\% & 1.00 & 1.00 & 1.14 & 1.00 & 1.00 & 1.00 & 1.00 & 1.00 \\ \hline
90\% & 1.25 & 1.14 & 1.14 & 1.00 & 1.50 & 1.33 & 1.33 & 1.00 \\ \hline
98\% & 2.38 & 2.71 & 3.29 & 3.00 & 4.00 & 3.00 & 3.67 & 4.00 \\ \hline \hline \end{tabular}
\end{table} 
Table 7: Stroke group’s number of muscle synergies for 80%, 90%, and 98% VAF with constant confidence interval of 90%. \begin{table}
\begin{tabular}{c c c c c c c c c} \hline \hline \multirow{3}{*}{**Group**} & \multicolumn{6}{c}{**Walking Condition**} \\ \cline{2-9}  & \multicolumn{2}{c}{**FW**} & \multicolumn{2}{c}{**BW**} & \multicolumn{2}{c}{**FT-W**} & \multicolumn{2}{c}{**BT-W**} \\ \cline{2-9}  & **Pre** & **Post** & **Pre** & **Post** & **Pre** & **Post** & **Pre** & **Post** \\ \hline Healthy & 3.02(0.84) & 3.00(0.81) & 3.25(0.75) & 3.06(0.82) & 3.41(0.82) & 3.26(0.63) & 3.65(0.58) & 3.42(0.73) \\ \hline Stroke & 2.38(0.74) & 2.71(0.95) & 3.29(1.50) & 3.00(0.00) & 4.00(1.51) & 3.00(0.00) & 3.67(1.03) & 4.00(0.00) \\ \hline \hline \end{tabular}
\end{table} 
Table 8: Healthy and stroke groups’ muscle synergies (98% VAF), pre- compared to post-training for walking conditions (FW, BW, FT-W, BT-W). Means are shown with standard deviation in parentheses. the coordinated recruitment groups of specific leg muscles with specific activation balances and specific activation waveforms were observed. The flexible combination of a number of muscle synergies led to a simplified selection of the appropriate muscle commands for a given behavioral goal (overground walking in older adults). Our study aimed to determine if muscle synergies could be used to quantify changes in high fall-risk groups (healthy older adults and older adults that had suffered a stroke) post-balance training. Within each group (healthy and stroke), muscle activations and muscle synergies were quantified, and some significant changes were observed. Previous studies have suggested that muscle synergy analysis indicates that changes in muscle activation patterns are due to the recruitment of fewer muscle synergies compared to healthy individuals [1]; we observed this here in that we saw increases in muscle activation post-training with corresponding decreases (on average) for the number of muscle synergies. The number of muscle synergies lends insight into the complexity of neuromuscular control needed/required while performing a specific task (i.e., a lower number of synergies equates to a more simplified control strategy). Therefore, decreases in muscle synergies used to execute walking could indicate a better ability for the participants to perform a certain task. There are some limitations that should be acknowledged in our study. Firstly, there was an imbalance in sample size between the healthy versus stroke participant groups, as well as in terms of female versus male participants. This may affect the overall generalizability of our findings. Further, we did not specify a requirement in terms of the type of stroke experienced by participants, just that participants that had suffered a stroke were at least 6 months post-stroke (i.e., in the chronic phase).