# Review of sEMG for Robot Control: Techniques and Applications
## 3 Processing and Pattern Recognition Methods
### Data Acquisition  
Many types of sEMG sensors have been applied in previous studies. Single-channel sEMG sensors focus on a particular area of muscle to try to eliminate the signals from uninterested muscles. This sensor is typically used in groups to form a multichannel acquisition system and simultaneously collect sEMG signals from different body parts. In contrast, high-density sEMG sensors can acquire spatial and temporal EMG information of a certain area using an electrode array that includes dozens of electrodes. Most researchers choose a commercial product that is quite mature compared with several self-made sensors. The Myo armband is a widely used product in hand gesture recognition based on sEMG [31; 32; 33]. Delsys Inc. provides various sensors for different situations [11; 13; 34; 35]. In addition, some devices can provide biofeedback signals to stimulate the muscles of patients to help them perform rehabilitation exercises [36]. The knee, ankle, shoulder, elbow, wrist, and finger joints support most movements in activities of daily living. Therefore, muscles attached to the bones that make up these joints have been extensively studied for a long time. Table 1 shows the muscles of interest in some papers published in the last 20 years. From the table, it can be concluded that, for the upper limb, these muscles are the biceps brachii, triceps brachii, and deltoid; for the lower limb, the most interesting muscles are the quadriceps femoris, anterior tibial, and gastrocnemius; for the wrist and finger joints, these muscles mainly refer to the flexor/extensor carpi ulnaris/radialis and extensor digitorum. In addition, some authors have performed their work on other muscles of the human body. [PERSON] studied speech recognition based on sEMG signals of the facial and neck muscles [13]. [PERSON]'s paper contributes to the load of the waist and abdomen muscles during repetitive weightlifting [12]. For studies in the field of hand gestures, the first dorsal interosseous, thenar, and hypothenar have also received attention from researchers. \begin{table}
\begin{tabular}{c c c c} \hline
**Body Part** & **Joint** & **Muscles** & **References** \\ \hline \multirow{8}{*}{Upper-limb} & \multicolumn{3}{c}{flexor carpi radialis} \\  & \multicolumn{3}{c}{flexor carpi ulnaris} \\  & \multicolumn{3}{c}{flexor digitorum superficialis} \\  & \multicolumn{3}{c}{flexor digitorum profundus} \\  & \multicolumn{3}{c}{extensor digitorum} \\  & \multicolumn{3}{c}{first dorsal interosseous} \\  & \multicolumn{3}{c}{hypothenar} \\  & \multicolumn{3}{c}{extensor digiti minimi} \\  & \multicolumn{3}{c}{long palmar} \\  & \multicolumn{3}{c}{spininator} \\  & \multicolumn{3}{c}{abductor pollicis brevis} \\ \hline \multirow{8}{*}{Wrist} & \multicolumn{3}{c}{flexor carpi radialis} \\  & \multicolumn{3}{c}{extensor carpi radialis} \\  & \multicolumn{3}{c}{flexor carpi ulnaris} \\ \cline{1-1}  & \multicolumn{3}{c}{extensor carpi ulnaris} \\ \cline{1-1}  & \multicolumn{3}{c}{pronator trees} \\ \cline{1-1}  & \multicolumn{3}{c}{extensor digitorum} \\ \cline{1-1}  & \multicolumn{3}{c}{flexor digitorum} \\ \hline \end{tabular}
\end{table} 
Table 1: Summary of muscles of interest in sEMG studies. To obtain a higher signal-to-noise ratio (SNR), references [6; 20; 101; 102] carried out a strict experimental protocol: shaving off the hair on the limbs, polishing the skin of the target area with sandpaper, wiping it with an alcohol pad, and finally, applying the medical gel. The authors of these studies believe that these steps are necessary for collecting satisfactory data, but most scholars have not executed such tedious operations in their experiments. Although there are some differences in the experimental protocols, researchers should be able to reach a consensus that the position of the sEMG sensor should be relatively fixed in each experiment. To maintain the same position in different trials, reference [73] divided the subject's forearm into seven areas according to their body structure and marked them with different colors.