## 2 Materials and Methods  
### Experiment Description  
Twelve males and ten females, aged on average 35 \(\pm\) 9 years, were included in the study. Selection criteria ensured gender balance in the dataset, ages ranging from 20 to 65 years, and no reported upper limb pathologies. Prior to participation, all subjects gave their informed written consent for the study, which was approved by the ethics committee of our university (reference number CD/31/2019). Participants performed seven representative grasps of ADL (Figure 1), based on the grasp taxonomy by [PERSON] et al. [27]: two and three fingers pad-to-pad pinch (PpP), cylindrical grasp (Cyl), lumbrical grasp (Lum), lateral pinch (LatP), oblique palmar grasp (Obl), and intermediate power-precision grasp (IntPP). Muscle activity was recorded using an eight-channel sEMG device from Biometrics Ltd., sampling at 1000 Hz. Integral dry reusable sEMG electrodes (SX230) were employed, featuring a gain of 1000, a bandwidth ranging from 20 Hz to 460 Hz, and noise levels below 5 \(\upmu\)V. Grasp effort was measured using hand grip and pinch dynamometers (Figure 2) also from Biometrics Ltd. Signals from the sEMG electrodes and dynamometers were synchronized using the provided Biometrics software version 11.02. The sEMG electrodes were positioned using a grid drawn on the forearm, guided by five easily identifiable anatomical landmarks. Subjects were seated comfortably with their elbow resting on a table, their arm flexed at a 90\({}^{\circ}\) angle relative to the forearm, and the palm of the hand facing them. The grid defined 30 different spots covering the entire  
Then, subjects performed the seven grasps with the right hand following precise instructions from the operator: the subject was asked to hold a dynamometer simulating the grasp to be analyzed, with the arm aligned with the trunk and the forearm flexed 90 degrees relative to the arm. They were instructed not to exert force initially and then to exert maximum effort while maintaining this posture for three seconds. To prevent unnecessary muscle contractions, the subjects were asked to then progressively increase the effort during 3 s, until they reached 50% of the previously recorded maximum effort with the dynamometer, maintain it for 3 s, and then gradually decrease it back to rest (Figure 4). Each grasp was repeated three times consecutively (only the 50% of the maximum effort), with a 3 min break between repetitions to avoid muscle fatigue. Subjects were allowed to practice each grasp as many times as necessary before recording. In order to obtain the muscle activity, sEMG signals were normalized using seven records of maximum voluntary contraction (MVC) measured for each subject before performing the grasping efforts: flexion and extension of the wrist, flexion and extension of the fingers, pronation of the forearm, ulnar deviation of the wrist, and elbow flexion. Subjects were instructed to exert maximum effort with the muscles of the forearm and hand while maintaining the same comfortable posture. Rest intervals of 1 min were incorporated \begin{table}
\begin{tabular}{c l} \hline \hline
**Scheme** & **Spot Muscles** \\ \hline
1 & Flexor carpi ulnaris (FCU) \\ \hline
2 & Flexor carpi radialis (FCR), palmaris longus (PL) \\ \hline
3 & Flexor digitorum superficialis (FDS), profundus (FDP), and flexor pollicis longus (FPL) \\ \hline
4 & Abductor pollicis longus (APL), extensor pollicis longus (EPL) and brevis (EPB) \\ \hline
5 & Extensor digitorum communis (EDC) \\ \hline
6 & Extensor carpi ulnaris (ECU) \\ \hline
7 & Brachioradialis (BR), pronator trees (PT), and extensor carpi radialis (ECR) \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Possible underlying muscles beneath each recorded spot, as indicated by a previous work [18]. Figure 4: Example of the experiment. Each line corresponds to the measurement of the muscle activity of each spot for one subject during the grasping activity. The grey square corresponds to the 3 s used in the subsequent analyses. between each MVC to prevent muscle fatigue.