###### Abstract
It is worth mentioning that a haptic device is accessible only for post-stroke patients with moderate or mild impairment, which means that the patient has sufficient motor and neurological functions to perform the activities of virtual scenarios [23]. To reduce the cost of systems that use haptic devices, some authors employ vibration motors to provide vibrotactile haptic feedback to touching virtual objects [24], in prosthetics with stimulation to the stump [25], and to improve standing balance [26]. Another advantage is the size of the motors, because they do not hinder user movements. That is why vibrotactile feedback is a solution for a low-cost system that gives cues about the virtual objects and VE to the user. With the addition of another feedback modality, such as vision, vibrotactile feedback is more effective [27], reflecting in the improvement of performance and in the reduction of real-time errors [28]. The development of a rehabilitation system with VR and haptic feedback seems an appropriate method to integrate strategies that maintain the patient's motivation, that allow them to observe their performance in the therapies continuously, and improve their quality of life. In recent decades, researchers have developed different systems to enhance rehabilitation and integrate robotic devices with VE. Game-based applications for rehabilitation use interactive games to maintain or increase a patient's motivation or try to simulate daily living activities [29,30]. However, some of these systems use commercial video games, representing a disadvantage because they are designed for healthy users without considering the therapists' needs, the participant's opinions and the range of motion. Therefore, their feedback cannot reflect improvements in the patient's motor control [3,31,32,33,34]. Another point to consider is that, in developing rehabilitation systems, the therapist's experience must be part of developing the new technology in rehabilitation. According to therapists, barriers for a system's inclusion in rehabilitation are the need for technical knowledge, the difficulty to use it, the time to set it up, and the support required by the system [35]. In most cases, characteristics like the range of motion [33; 34] and users' abilities and capacities [3; 36] have been considered to develop these systems. It is not until the system is finished that User-Centered Design (UCD) is used to evaluate and improve it [37; 38], or just to perform data analysis [33]. For instance, the evaluation of the system considers family members with post-stroke relatives [34] or stroke survivors [33], but does not consider therapists' participation during the development, which is crucial because they provide feedback and ensure that the system fulfills its purpose. The main contribution of this article is that the VE for UL rehabilitation was developed, taking into account the requirements obtained from therapists using UCD, for instance, the desired movements. The VE proposed uses a haptic device and it is designed to be used in a clinical environment. For the design of the system proposed, several factors were taken into account, such as: (a) the capacity of the patient (ranges of motion), (b) the psychological properties of the color for the Graphics User Interface (GUI), (c) motor learning principles, such as repetition and feedback [39], and (d) performance characteristics of the communication channels between the VE and the user (bandwidth and transmission delays for haptic feedback, visual and auditory feedback) [40]. The main difference in the proposed rehabilitation system's development process from others available in the literature, is the therapists' feedback in all its stages. Once the first version was ready, the usability and functionality were evaluated. Then, according to users' results and feedback, necessary changes were identified and implemented. Finally, the usability, user experience, and functionality of the system were evaluated by volunteers.