## 4 Immersive Virtual Reality: Hardware and Software Perspectives
### Overview of Immersive Virtual Reality Software
Other authors emphasize that commercially available VR games often promote nonspecific, and at times undesirable, movements, lack patient-specific customization options, and may lead to frustration for individuals with motor impairments [128]. The limitations of commercially available VR games also extend to their restricted utilization of specific VR mechanisms. Most off-the-shelf games are primarily applied in studies for purposes such as education, relaxation, distraction from pain and enhancing patient engagement. However, these applications fall short of achieving the more targeted therapeutic effects that VR has the potential to offer. For instance, when using VR for pain distraction during exercise, a common challenge is that many commercially available games promote only single-joint movements or repetitive actions. This limitation makes it difficult to replace a comprehensive exercise program with a single VR game that adequately supports the diverse range of movements necessary for individual patients. Consequently, VR can often supplement only a portion of the exercise regimen, with additional exercises needing to be performed outside the VR environment to ensure a complete therapeutic approach. Furthermore, VR technology allows for manipulation of somatosensory input, enabling therapists to display movements in the VR environment that a patient may be unable to perform in reality, or to adjust the perceived range of movement by making it appear understated or exaggerated, as demonstrated in studies with neck pain patients by [PERSON] et al., (2023) [14] and [PERSON] et al., (2020) [24]. Creating bodily illusions through VR can be especially beneficial in modifying patients' movement, body or pain perceptions, offering therapeutic advantages for individuals with musculoskeletal conditions, particularly those with kinesiophobia, altered body perception or chronic pain [14; 129; 130]. However, we have not encountered any applications on the market that incorporate body illusions specifically for patients with musculoskeletal conditions or chronic pain. Although _Mirage Lab_ offers tools for creating bodily illusions, these experiences are not fully immersive but rather fall within AR, primarily aimed at research purposes and focused on illusions for the hand, as described on their website [131]. Companies that market VR software for therapy and rehabilitation in chronic pain and musculoskeletal conditions tend to focus on VR for exercise interventions (e.g., cardio, range of motion improvement, strength training, or graded exposure therapy), with examples including, but not limited to, _Corpus VR_, _XRHealth_, _SyncVRMedical_, _KineQuantum_, _Neuro Rehab VR_, _Dynamics VR_, _KarunaHOME_ and _Virtualis_. Others concentrate on pain education, such as _XRHealth_, _Reality Health_, _Dynamics VR_, _RelieveVRx_, _KarunaHOME_ and _Reducept_, while some provide programs for meditation, relaxation, or stress management, including _Neuro Rehab VR_, _Corpus VR_, _XRHealth_, _VRelax_, _RelieveVRx_, and _Dynamics VR_. Some applications, such as _RelieveVRx_ are designed to help patients develop the skill of shifting their focus away from pain. It appears that there is still considerable opportunity for the VR software market in musculoskeletal rehabilitation to expand, as it is currently underrepresented and lacks comprehensive solutions tailored to specific health conditions. Therefore, it would be beneficial for future development efforts to focus on creating more specialized, integrated software solutions that address the unique therapeutic needs of musculoskeletal patients. It is important to note that many companies offering software for patients, and advertising their programs as suitable for specific musculoskeletal conditions, often do not provide detailed information about the software content (e.g., the specific movements patients perform during use). Companies identified on the market typically offer demo versions of their software, but access to these demos generally requires contacting each company individually.