## 2 Materials and Methods
### Data Gathering Outlines
The hand gestures studied, illustrated in Figure 1, can also be found in our prior study on supervised hand gesture decoding [14]. Figure 1: This figure illustrates the selected hand gestures performed during post-stroke movement attempts on both the affected and non-affected sides. The gestures are displayed in the sequential order of the EMG recordings: (**a**) resting state (rest), (**b**) clenched fist, (**c**) index pinch, (**d**) wrist flexion, (**e**) wrist extension, (**f**) spread hand (fingers opening), and (**g**) upright thumb (thumbs up). EMG data collection was conducted among stroke patients, including those with ischemic and hemorrhagic types of stroke which resulted in upper extremity motor function deficits. The inclusion criteria were as follows: age over 18 years, a registered incident of a cerebrovascular accident within the last eight weeks, and the ability to fully understand the experimental procedure for EMG signal gathering along with a functional assessment [5]. Myoelectrical activities were recorded using an \"8 CH HUB 19022021\" EMG device (PLUX Wireless Biosignals S.A., Lisbon, Portugal) at 1 kHz, with an operative voltage of \(\pm\)1.5 mV. Ag/AgCl soft electrodes were placed on the flexors and extensors of the forearm and the the shear area of the palm [13; 14]. Except for the resting gesture, recorded at the beginning of observational sessions, ADL-related gestures were performed sequentially, with each gesture repeated 10-20 times to ensure a balanced set of 10 gestures per class, providing equivalent per-class EMG signal data for training and testing. Hemiplegic patients repeated hand movements alternately on both extremities (Figures 2 and 3). Data collection was conducted in hospital settings under two approved clinical protocols of the University of Tsukuba Hospital: R04-041 and R02-204. In study R04-041, recordings from stroke survivors were collected twice with an interval of at least 10 days, whereas in study R02-204, recordings from the same subjects in an observational clinical study were collected only once. All recordings, patient selection, and collection of patients' written informed agreements were guided by the University of Tsukuba Hospital Ethics Committee and Review Board and the Declaration of Helsinki. The Japan Registry of Clinical Trials (jRCT) ID is jRCT1030220380. Details of the study participants can be found in Section 3.1 of the Results. An illustration of the proposed study can be found in Figure 4.  
Figure 2: The representative EMG recordings performed by stroke patients using their unaffected upper extremity, with each gesture executed in sequential order. The x-axis represents the recording time in seconds (s), while the y-axis denotes the EMG amplitude in mV. Surface EMG signals were acquired using bipolar electrodes placed over four specific forearm muscle regions: Channel 1 over the flexor carpi radialis, Channel 2 over the flexor carpi ulnaris, Channel 3 over the theanr eminence targeting the abductor pollicis brevis and flexor pollicis brevis, and Channel 4 over the extensor digitorumum. The initial recording segment captures the pre-calibration and resting state. Figure 4: Settings of the clinical trial assessing bilateral data fusion in subacute stroke. Using an 8-channel EMG device (8 CH HUB 19022021), four bipolar surface electrode pairs were placed on each forearm and hand. After patients were positioned at the table in the controlled environment, they performed sequential hand movements or movement attempts with their unaffected (i.e., non-paretic) and affected (i.e., paretic) upper extremities, completing at least 10 attempts per gesture class. After recording, the data were processed into an EMG dataset and split into training (data from both extremities) and testing sets (data from the affected extremity only). This was followed by 10-fold cross-validation, iterated 100 times, to correctly classify the intentional paretic gesture for each attempt using DL, leveraging the bilateral data fusion approach.