## 2 Materials and Methods  
### Experimental Protocol  
An experimental study was conducted with fifteen volunteers. The data of only four women and six men were retained for consideration here. Although the smaller sample size complicates summarizing the findings, may not properly represent the target group, and limits the generalizability for a larger set of volunteers, the other five participants were excluded from further consideration. The reasons for exclusion were various - the existence of numerous artifacts in the raw sEMG signal, the inability to perform the movement in the required tact, and inaccurate positioning of the limbs. Commonly, sEMG artifacts can be caused by the following factors: improper electrode placement, power line interference, cross-talk, noise originating from devices in the surrounding area, physiological artifactscoming from the heartbeat, breathing movements, sweating, static electricity charge, electrodes, cables, and skin movement. To reduce all these possible artifact appearances, we strictly stuck to the Seniam protocol for skin preparation and electrode placement [36]; used the battery mode of computer operation to avoid 50 Hz contamination; recorded big, easy to find surface muscles to avoid cross-talk; switched off any electrical devices, as well as not using an internet connection; investigated the right arm muscles so no heart rate was registered; avoided synthetic materials; and used Butterworth filters to reduce artifacts of the shaking of the skin, subcutaneous tissue, and muscles. All the participants were in a good general condition and had no related musculoskeletal or neuronal complaints. The subjects were thoroughly informed about the upcoming procedure and provided their informed consent. They were then asked to complete a series of eighteen motor tasks (MTs)-calm position, evoking maximal isometric contractions, eight cyclic movements (CMs) in the sagittal plane, and eight CMs in the horizontal plane. The Scientific Council of the Institute of Biophysics and Biomedical Engineering approved the investigation. Until now, two articles have been published detailing the first part of the motion protocol performed in the sagittal plane [5; 6]. This article focuses on movements performed in the horizontal plane. The sEMG signals were registered by the circle electrodes \"Skintact-premier\" F-301 Ag/AgCl and the Telemyo 2400G2 system of Noraxon Inc. (Scottsdale, AZ, USA). As the SENIAM protocol recommends [36], the electrodes were placed over precisely defined areas of the previously chosen surface muscles. The skin underwent preparation aiming for better contact with the electrode and obtaining a good output signal. If necessary, the skin area was shaved and treated with alcohol. Electrode gel was then applied, and the electrodes were placed over the following muscles: m. deltoidebus pars clavicularis (DELcla), m. deltoideus pars spinata (DELspi), m. brachialis (BRA), m. anconeus (ANC), m. biceps brachii (BIC), and m. triceps brachii long head (TRI). The angle at the elbow joint was also measured with a 2D goniometer, again produced by Noraxon Inc. The goniometer was calibrated for each person before the start of the experimental series. The experimental series was explained and demonstrated to the participants in detail. Before the start of each recording, the participant performed as many repetitions of the movement as necessary to complete the required time interval of one minute, which was conducted with video and sEMG data recordings. Here, we will discuss only the MTs performed in the horizontal plane and the tasks used further for sEMG signal normalization. Each participant sat on a stable chair without armrests. The spine was kept straight, and their gaze was directed forward. The arms were freely relaxed next to the body, and the feet were firmly placed on the floor. All MTs were performed with the dominant arm of the person--the right one. 1. MT 1: Calm position. The subject was sitting on a chair. He took the position described above and kept it for one minute.