## 2 Materials and Methods
### Intervention
#### 2.3.2 Upper Limb Rehabilitation Gaming System  
The RGS is a semi-immersive VR approach to UL impairment that has shown its benefits as a valid tool to provide sensorimotor training and feedback [22; 52; 53]. This system tracks arm and finger movements to translate them to an artificial environment, so the virtual limbs are controlled in a first-person perspective. The RGS set-up consists of a monitor integrated with a computer where games are displayed. Motion capture is tracked by a Kinect motion capture system (Microsoft, Redmond, WA, USA) and a Leap Motion device (Ultraleap, San Francisco, CA, USA) [54]. The Kinect motion capture system enables body tracking with a depth sensor, a matrix of microphones with a video camera and an orientation sensor. The Leap Motion controller is a hand tracking device composed of two cameras and some infrared LEDs. Exercises involving distal movements with wrists, hands, and fingers use a supplementary forearm support, so movement is correctly captured and posture during executive is correct. The body movements' recording is included in a gamified environment with several games involving the trunk, shoulder, elbow, wrist, hand, and fingers. The user's movements are captured and included in the virtual environment for achieving the specific objective depending on the selected game [22].  
During the intervention, the participant will be seated in a comfortable position in front of the monitor where the VR will be displayed. The exercises will include reaching, grasping and realising, pronosupination, and fine motor skills. The VR training will be administered in 40 min sessions. The games included in the VR training are divided into UL training and hand-specific training. The UL training is conducted with the Kinect azure camera, and consists of the following games:  
* Boat: the participant is asked to drive a boat moving laterally the trunk and to catch all the items during the exercise with both ULs. This exercise approaches reaching against gravity without support with flex-extension of the elbow and flex-extension and abduction of the shoulder, trunk control, and balance. Total duration: 4 min.
* Hockey: The participant is asked to hit the puck to reach the goal. This game exercises reaches with the table support, with flex-extension of the elbow and flex-extension and abduction of the shoulder. As the participant musts adapt to the return of the puck to hit it again, the reaction time and velocity are also trained. Total duration: 5 min
* Pinball: The participant is asked to reach a ball of a specific colour. This exercise trains reach the same way as the previous game. Total duration: 5 min
* Spheroids: The participant is asked to catch the balls and put them in the container of the same colour as the ball. This exercise trains reaches against gravity without support, with flex-extension of the elbow and flex-extension and abduction of the shoulder. Total duration: 5 min  
The hand-specific training is conducted with the Leap Motion controller and the previously mentioned forearm support. This training consists of the following games:  
* Robot: This exercise is conducted with a forearm support. The participant is asked to perform a thumb and index finger pinch to grab different objects to win points and facilitate the way to a kitten. This exercise aims to train fine motor skills. Total duration: 7 min
* Spaceship: This exercise is conducted with a forearm support. The participants are asked to turn the spaceship left or right to avoid asteroids and win points. This exercise trains the monosupination of the forearm. Total duration: 7 min
* Monkey: The participant is asked to close the hand when the monkey reaches a branch and realise the hand grip to jump to the next one. This exercise trains the hand grip. Total duration: 7 min  
Working memory, attention, executive functioning, and inhibition are trained across every game.