## 4 Discussion
### Muscle Contribution
EDC is the extensor muscle of the MCP joints of the fingers and also contributes to the extension of the DIP and PIP joints of the fingers, along with the lumbricals and interossei [32]. APL and EPB participate in the abduction and extension of the thumb carpometacarpal (CMC) joint while EPL functions as an extensor and adductor of the thumb MCP joint [34]. An outcome of this study suggests that, during grasps, these muscles also act as antagonists to the finger flexors, counteracting the required flexor moment and ensuring adequate stabilization. This is particularly crucial during precision grasps [36], as the thumb is typically abducted and/or extended during these grasps, engaging in thumb opposition. ECU (spot 6) presented maximum activity during the cylindrical grasp, two/three-finger pad-to-pad pinch, and oblique-palmar grasp. ECU has the largest moment for ulnar deviation and is an effective wrist extensor only in supination [34]. In these grasps, which require considerable effort from the finger flexors, ECU seemed to play a crucial role in stabilizing the wrist and fingers. By doing so, it countered the moment exerted by the finger and wrist flexors, contributing to the overall stability of the grasps. An application of the results could be to aid in identifying the key muscles required during each grasp. This could help focus on enhancing the muscular capacity of those muscles or spots that contribute most to each grasp, either through specific exercises or electro-stimulation. For example, to increase the strength of power grasps, which are essential in ADLs requiring more force, such as using a hammer, it is not enough to stimulate the flexors; it is also necessary to stimulate the extensors, which act as antagonists to stabilize the grasps [32]. Furthermore, the mean values obtained from each forearm spot could be used as normative values of muscle activity for a global population, which will illuminate the demand required for common tasks, thus providing baselines for evaluating \begin{table}
\begin{tabular}{c l l} \hline \hline
**Grasps** & \multicolumn{2}{c}{**Observation about Role of Muscles**} & **Muscles More Activated** \\ \hline two-finger PpP & \begin{tabular}{l} Thumb abductors and extensors play a crucial role in stabilizing the grasps \\ by counteracting the forces generated by the index finger. \\ \end{tabular} & ECU, EDC, BR, PT, ECR \\ \hline two-finger PpP & \begin{tabular}{l} The action of the middle finger increases the maximum force generated \\ while reducing the activity of the thumb abductors and extensors. \\ \end{tabular} & ECU, EDC, BR, PT, ECR \\ \hline Cyl & \begin{tabular}{l} The most powerful grasp. It involves FCU and ECR to stabilize the wrist. \\ Finger flexors and thumb extensors and abductors exert similar and \\ maximum activity. \\ \end{tabular} & BR, PT, ECR, EDC, FCU, FDS, \\ \hline Lum & \begin{tabular}{l} ECR and ECU are required to extend the wrist. Finger and thumb extensor \\ act to extend the fingers (PIP and DIP joints). \\ \end{tabular} & BR, PT, ECR, EDC, ECU \\ \hline LatP & \begin{tabular}{l} Presents low activity from all the extrinsic muscles. Extensors are more \\ active than flexors in stabilizing the wrist for grasp execution. The thenar \\ and intrinsic muscles are the primary contributors to grasp force \\ (up to 80\%) [35]. \\ \end{tabular} & BR, PT, ECR, EDC \\ \hline Obl & \begin{tabular}{l} Behavior similar to Cyl grasp but thumb placement reduces its \\ muscular contribution. \\ \end{tabular} & \
\begin{tabular}{l} BR, PT, ECR, FCU, ECU, EDC, \\ FDS, FDP, FPL APL, EPL, EPB \\ \end{tabular} \\ \hline IntPP &
\begin{tabular}{l} FCU and ECR presents maximum forces to stabilize the wrist. Finger \\ flexors and extensors require similar activity. \\ \end{tabular} & FCU, APL, EPL, EPB, BR, PT, \\ \hline \hline \end{tabular}
\end{table} 
Table 5: Summary of findings regarding muscles that are more activated and their respective roles in each grasp. clinical populations.