## 1 Introduction  
The occurrence of patients who have survived brain injury or undergone lower-extremity joint surgery is rapidly increasing due to aging, accidents, and stress. Rehabilitative training for such patients is vital, with gait training being the most essential form of such rehabilitation [1]. Gait training and rehabilitation focusses on strengthening and restoring intrinsic motor functions with exercises to enhance skeletal movement, along with muscle contraction and relaxation, within the normal range of motion (ROM) of the joint [2]. Additionally, the market for gait rehabilitation devices is rapidly expanding. In preparation for this trend, it is necessary to develop an effective, inexpensive device so that it can be widely used in gait rehabilitation [3]. The most important factor in gait rehabilitation training machines (MGTRs) is the implementation of a normal gait pattern [4]. These devices exist as two types: exoskeletal and end-effector. The exoskeletal type consists of three actuators--one each on the hip, knee, and ankle--that control the movement of the entire joint, while the end-effector type controls joint movement by adjusting the shape of the sole when it touches the ground [5]. Gait rehabilitation aims to realize the form of normal gait, and the effects recreated by both types of devices are very similar to those of normal gait [6, 7]. MGTR systems assist patients with gait disorders (such as stroke and Parkinson's) by helping them develop gaits that are similar to the normal gait; this improves their brain plasticity and muscular activity while reducing imbalance [8]. However, patients face problems such as boredom and familiarity while undergoing repetitive rehabilitation exercises; this leads to a decrease in their immersion and motivation, which impairs their rehabilitation [9]. Therefore, a patient's immersion, motivation, and sense of achievement with the rehabilitation exercise strongly influence the success of said exercise [10]. This brings to light the need for technologies that enable cognitive immersion during rehabilitation exercises to motivate patients and provide them with a sense of achievement; virtual reality (VR) technology is one such element [11; 12]. VR provides users with a simulated experience (that can be as similar to, or different from, their actual environment as required) in a virtual visual setting. Immersion is generally provided by synchronizing this setting with the user's visual and motor movements, with sensory feedback provided by a haptic device [13]. VR provides a simulated environment with essential feedback for learning and motivation; this has enabled its use in several real-world scenarios [14]. It goes beyond the limits of a system that provides only visual feedback in a simple static state, and instead synchronizes with the dynamic changes in a user's surroundings to provide them with a sense of immersion. It can also solve the spatial and safety problems that occur during gait rehabilitation. In addition, it also helps measure (and biomechanically analyze) user gait, enabling an awareness and sharing of it between patients, therapists, and doctors [15]. The effect of rehabilitation treatment is enhanced by the convergence of the MGTR and VR systems. When MGTR and VR trainings were provided as interventions for 24 children with neurological gait disorders, the stance and swing phases of their gaits were significantly improved compared to the results achieved from the exercise and image therapy provided by their therapist [16]. In addition, it was confirmed that motivation increase, perceived pressure and emotional strain decreased when the MGTR was implemented along with VR for 20 subacute stroke patients [17]. As such, VR-MGTR convergence requires a biofeedback system that feeds back the gait state in real time; this enhances rehabilitation when compared to exercising without VR ([PERSON] (2020)).