Military service commonly involves engagement in high-risk activities, whether during physical training, daily trade-related tasks, overseas deployment, or in response to natural disasters. Such activities place military members, individually and collectively, at a heightened risk of physical and psychosocial injury. They are also more likely to have increased exposure to highly traumatic and stressful events [1] and exhibit higher rates of injuries and illnesses, such as posttraumatic stress disorder (PTSD), depression, anxiety, sleep disorders, and mild traumatic brain injury compared with civilians [2,3]. In Canada, approximately 11% of military members and 16% of veterans experience PTSD [4]. In the United States, the prevalence of combat-related PTSD ranges from 1.09% to 38.84% [5]. The rate of probable PTSD among UK military personnel has been reported to be 6.2%, and among veterans who had been deployed in combat roles, it was 17.1% [6,7]. In Australia, approximately 8.3% of Defense Force members will have experienced PTSD [8]. Among currently serving and retired military personnel in New Zealand, 30% had symptoms of posttraumatic stress, and 10% had clinically relevant posttraumatic stress [9].

Hypervigilance, impaired cognition, comorbid mood and anxiety disorders, and significant functional and relational sequelae are associated with PTSD [1]. Military members and veterans are also more prone to developing moral injury than civilians, which is the persistent distress that can evolve from exposure to potentially morally injurious events, including perpetrating, witnessing, or failing to prevent an act that transgresses core beliefs [10-13]. Up to 67% of military members are exposed to potentially morally injurious events during deployment, the sequelae of which have not yet been fully explored, although it has been suggested that moral injuries might contribute to treatment-resistant PTSD (TR-PTSD) [14,15].

The delivery of evidence-based therapies specifically targeting posttraumatic stress throughout the military health care system has been the focus of the Departments of Defense in numerous countries, including Canada, the Netherlands, and the United States. Greater than 66% of military members who complete first-line treatments for PTSD continue to experience symptoms that significantly affect their daily functioning and quality of life [16]. Even in those responsive to treatment, PTSD symptoms often persist at or above the diagnostic thresholds for PTSD, with approximately 60% of patients retaining the diagnosis [17,18]. The effectiveness of these first-line psychotherapies is hypothesized to be limited because of cognitive avoidance and premature treatment dropout [19,20]. The reasons for higher dropout rates among this population vary but may include geographical proximity to services, perceived stigma from self and others, challenges managing operational demands of a military career with therapy attendance, barriers to establishing patient-therapist rapport, and the aforementioned issues with treatment effectiveness [19,20].

The classification of TR-PTSD has been adopted for military members and veterans who do not experience a clinically significant reduction in symptoms following the receipt of at least two evidence-based treatments [21,22]. As knowledge of TR-PTSD is limited, general recommendations for TR-PTSD have been suggested. However, specific protocols or evidence-based TR-PTSD therapies are lacking, complicating clinical attempts to address or manage this condition. Consequently, more innovative and effective treatments are needed to assist military members, veterans, and other populations affected by trauma in rehabilitation and recovery from PTSD and occupational stress injury.

Multimodal motion-assisted memory desensitization and reconsolidation (3MDR) is a personalized, exposure-based, virtual reality (VR)–supported intervention developed in the Netherlands and is being used with military members and veterans with PTSD in the Netherlands, the United Kingdom, the United States, Israel, and Canada [23]. 3MDR enhances visual and auditory immersion by incorporating patient-selected images and music into the therapy and helps patients access traumatic memories as they walk toward images that remind them of those experiences [24]. The treatment shows promise for breaking through persistent avoidance and optimizing engagement in military members and veterans with TR-PTSD [25,26]. Two recently published randomized controlled trials conducted with veterans with TR-PTSD have contributed to the evidence base regarding the effectiveness of 3MDR [27,28]. Further studies are also underway.

For 3MDR, treadmill walking on a flat surface was chosen as the method of moving forward (literally and metaphorically) versus using other devices, such as a stair climber, which involves other movement patterns and requires more engagement of energy systems and cardiorespiratory abilities. As walking is a basic form of human movement that engages multiple processes and areas of the brain, it has been hypothesized that the act of moving forward through ambulation is integral to 3MDR and may increase divergent thinking abilities, thereby allowing previously held negative cognitions related to trauma to be challenged. In addition, a harness can be easily attached and added to a treadmill setup, making it a safer option than using other movement devices or virtual boundaries (ie, VR or augmented reality [AR] headset systems such as Oculus, Google Glass, or Microsoft’s HoloLens).

The 3MDR application was originally designed to be used on a large-scale, immersive VR–based system called the Motek Computer Assisted Rehabilitation Environment (CAREN; Figure 1) and the Gait Realtime Analysis Interactive Lab (GRAIL; Motek Medical BV) [29]. These were designed as dedicated solutions for gait analysis and training under challenging conditions to improve gait patterns. CAREN is a room-sized dynamic system that includes a motion platform that can translate and rotate in all directions. The platform contains an embedded, centrally located treadmill that moves in synchronization with the virtual environments projected onto a large curved screen. The package contains real-time feedback and user-friendly assessments and applications. The GRAIL originally used an instrumented dual-belt treadmill with optional pitch and sway, a motion capture system, video cameras, and synchronized VR environments (VREs). The treadmill’s ability to measure forces and the independent control of left and right treadmill belt speeds has allowed a split-belt walking protocol and advanced gait research applications that can mimic tripping or slipping. The 3MDR application has progressively evolved to include other hardware options (ie, CAREN Lite) since the initial proof of concept was piloted in 2011 [23]. These versions of 3MDR hardware allowed for preliminary research to assure participant safety with clear, tangible boundaries as opposed to virtual ones, as experienced within the VR or AR headset systems. This was especially important at the time of the intervention’s developmental process when there were still many unknowns about the participant’s experience of 3MDR and the responses it may elicit.

The 3MDR intervention comprises 10 sessions, including selecting images and music, trauma processing and reconsolidation, and six 90-minute therapy sessions in the VRE, including a 30-minute debriefing. The 3MDR sessions include a preplatform session (session 1), during which the patient selects and orders images and music. Symbolic representations in the form of images (ie, photographs and sketches) related to their traumatic experiences are selected and ordered from least to most distressing. Music that reminds the patient of the past time of trauma and facilitates the emotional memory network is also identified, which supports a return to the present (ie, a second contemporary piece that is soothing, compassionate, and joyful). Sessions 2 to 7 are platform sessions that involve 3 phases. In the preplatform phase of the session, the therapist and patient confirm the order of images and music for the session. During the platform phase, the patient dons a safety harness and is accompanied by a 3MDR therapist while walking continuously on a treadmill at a self-selected pace. The patient first warms up by walking on the treadmill while listening to self-selected music, which connects them to their traumatic experiences, and then, during each of seven 3 to 5 minutes cycles, walks down a virtual hallway toward a self-selected trauma-related image. The patient describes the image, physical sensations, and feelings to the therapist. The therapist then assists the patient with generating descriptive words and phrases that are then projected in front of the image on the screen. The patient is then instructed to read the words and phrases out loud. For a duration of 30 seconds, the patient then reads aloud numbers as they appear on a ball oscillating horizontally in the foreground of the image and words. The patient cools down after the seventh cycle by walking while listening to self-selected music, which facilitates a reconnection to the present. Each session concludes with a postplatform phase, which includes discussion, reconsolidation, a mental wellness check, and a self-care plan. Postplatform sessions 8 to 10 focus on reconsolidation and contribute to meaning making of the acquired gains and emotional release. More in-depth descriptions of 3MDR have been published elsewhere [25,30].

Recently, published randomized controlled trials have demonstrated the efficacy of 3MDR therapy among military and veteran populations who experience combat-related TR-PTSD and indicate that 3MDR is ready for trials with various populations affected by trauma in real-world contexts [27,28]. However, access to the CAREN VREs used to deliver 3MDR in earlier studies is limited because of the cost and infrastructure required by these large systems and the reality that only limited international partners in the Netherlands, Tel Aviv, the United States, the United Kingdom, and Canada have access to equipment currently used to deliver the intervention. 3MDR systems that are mobile, customizable, accessible, cost-effective, and adaptable to other populations affected by trauma are needed to increase accessibility to treatment. There is a sense of urgency in the 3MDR international consortium to develop further systems, particularly in light of their need within military and veteran populations, as well as among other populations affected by trauma. The COVID-19 pandemic has acted as a reminder that emergency medical professionals and first responders, among others, also require access to innovative and effective evidence-based treatments.

Despite the urgent need for accessible interventions for PTSD, a barrier to the expanded access to 3MDR in community-based health service contexts is the use of equipment and technologies approved by the United States Food and Drug Agency and Health Canada. Although these approvals are imperative to protect the health and safety of patrons of health care systems, the approval process requires the determination of appropriate hardware (eg, treadmills, projection systems, and AR equipment) and the development of software that is adaptable for various populations. Provision of research and evidence demonstrating equipment validity, safety, efficacy, and effectiveness specific to the target demographic is the first step toward improving access to novel interventions with technological applications. Now that research has demonstrated that 3MDR holds promise, new research may involve the exploration of adaptations including the delivery of 3MDR via more mobile, affordable, and immersive mechanisms, such as AR headsets, and to additional populations affected by trauma.

The purpose of this mixed methods study was to further innovate, develop, and validate new and existing hardware and software components of 3MDR to enhance the mobility, accessibility, feasibility, and applicability of 3MDR for other populations affected by trauma, including public safety personnel (PSP), via international collaboration.

This mixed methods study used a (1) modified Delphi expert consultation method and, (2) a mixed methods quasi-experimental software validation study [31].

This study was approved by the University of Alberta Research Ethics Board (Pro00084466) as part of a Canadian 3MDR study [30].

Hardware design based on expert consultation produced designs for two 3MDR systems: one using an external display (3MDR compact system) and the other using an AR headset (3MDR AR system). Both systems are described in the following sections.

The quantitative and qualitative study findings in the subsequent sections reflect participant feedback (N=35) regarding the new 3MDR software.

Over the past decade, 3MDR has evolved from an intervention requiring physically large and costly infrastructure to more mobile options. The CAREN and GRAIL systems offered an opportunity to trial 3MDR with military members with TR-PTSD using a VRE originally developed for physical rehabilitation. Technologies have since become more mobile, accessible, and cost-effective. Through the research and innovation of this 3MDR international collaboration, the existing hardware and software components of 3MDR were adapted, followed by new components being incorporated, modified, and further validated to enhance the mobility, accessibility, feasibility, and applicability of 3MDR for use with trauma-affected populations. This mixed methods approach, which included a modified Delphi approach, hardware and software development, validation, descriptive statistical analysis, qualitative thematic analysis, and triangulation of the data, allowed the research team to conceptualize, build, and evolve a new 3MDR system. Doing so has positioned 3MDR to be ready for the next wave of populations affected by trauma, which will require novel trauma interventions, including PSP affected by the COVID-19 pandemic.

New hardware and software will benefit from continued studies on feasibility, acceptability, usability, and validity. Although it is expected that the new 3MDR setup will provide similar results to those from previous studies that used the GRAIL, CAREN, and CAREN Lite, new and unpredicted variables could potentially change the experience and outcomes of 3MDR. For example, it remains unknown how patients may react to HoloLens 2 and other wearable metrics and whether this may disrupt the connection between them and their therapist. That said, 3MDR is a protocolized psychotherapeutic intervention. Despite the adaptations and changes in hardware and software, it is not anticipated that deviations from the protocol will result.

The salient hardware components of the 3MDR compact system were identified through expert consultation. These included the treadmill, safety harness, computer system, treadmill or computer interface, graphics card, visual display, and eye-tracking capability. The characteristics considered included access, physical footprint, portability, therapist positioning, system operation, cost, acceptability, and ease of use. The results yielded a more modular, cost-effective 3MDR compact system and a 3MDR AR system, both of which increased the potential for customized and tailored immersions for populations affected by trauma. The 3MDR compact system comprised a COSMED T150 clinical treadmill, together with a computer built around the Nvidia Quadro P5000 graphics card and short-throw light-emitting diode projectors with display screens [36,37]. Regarding the 3MDR AR system, a blend of virtual and real visual stimuli was determined to be essential, as was the ability of the patient and therapist to effectively see each other and read facial cues. The HoloLens 2 system, together with a laptop, router, and treadmill, were selected [32].

Through the modified Delphi consultation process, specific needs were identified that the new 3MDR software would have to meet to reach the goals of enhanced mobility, accessibility, feasibility, and applicability. The team identified (1) ease of adaptation to new technologies, (2) a user-friendly interface, (3) the ability to integrate audio and visual playback components, and (4) data capture and reporting capabilities as priorities for the software. The first was addressed via the integration of Unity 3D to allow for easy adaptation because of its flexibility, modularity, and polymorphism, enabling applications to maintain their relevance with evolving technical innovation. It also offers flexible integration of heart rate monitors, eye trackers, and other wearable devices for future use and can be ported to different devices and displayed using variable means. This would also address the key theme of individualized-tailored immersion, which was recognized by the PSP as a priority in software validation. The UI was designed to be easy for therapists to use, with higher resolution images and rendering. The music selection was integrated into the software. Furthermore, walking speed, notes, and biomarkers can be entered, automatically saved, and easily reviewed. Although many of the aspects incorporated into the software coincided with the results of the software validation study, not all assumptions of the team were matched to the data from the PSP (N=35). Although the research team opted to have a standard VRE display within the software with the music and images being customizable, the PSP expressed a desire to customize the environment to their professions and individual circumstances. The team and the PSP were similar in that they were passionate about 3MDR being adapted and used for other populations affected by trauma. The perceived strengths, weaknesses, and recommendations of the PSP participants will inform further modification and improvement of future 3MDR software.

There were several barriers and limitations that were faced throughout this initiative. The software validation study used a relatively small sample size, and the COVID-19 pandemic necessitated that focus groups be web-based opposed to in person. This meant that some potential participants could not engage because of reduced access to devices; bandwidth; and wired or wireless internet that would allow them to view videos, complete the web-based forms, and engage in focus groups. In addition, pandemic restrictions provided barriers to physically accessing research facilities, which precluded the validation of hardware. In the future, further validation of the hardware and software will be addressed through ongoing consultation with patients, clinicians, and policy makers as further development of 3MDR is pursued.

Future research and evolution of 3MDR will continue to enhance accessibility and cost-effectiveness while ensuring the effectiveness of 3MDR and patient safety, thereby positioning 3MDR for continued development as technologies emerge. Further study and development will involve populations beyond the military and PSP to include other civilians who have experienced gender-based violence, adverse childhood experiences, natural disasters, global conflicts, intergenerational trauma, and other complex traumas that require novel approaches to rehabilitation and recovery. In addition, 3MDR has traditionally been used in adult populations aged 18 to 65 years. Further studies will involve the efficacy of this intervention for other periods of the life span. Increased mobility and portability will also increase the ability of populations in geographical areas with limited information technology infrastructures, such as remote rural areas and combat zones, to potentially use 3MDR. This may include VR or AR headsets, which are becoming more accessible and common to general consumers. Future studies may also address levels of immersion among different populations affected by trauma with the evolving 3MDR hardware and software to determine whether these modifications influence the efficacy of the intervention.

Future opportunities for 3MDR evolution and research may involve the use of eye tracking and other wearable biosensor systems with the aim of providing therapists with real-time information regarding neurobehavioral indicators and trends. For example, eye-tracking information could provide the therapist with information on the visuoperceptual processing of the patient, including whether they are avoiding certain aspects of the image or neglecting part of the screen and facing challenges tracking the EMDR ball. The use of electroencephalography could potentially measure changes in brain activity to better assess the components of 3MDR that affect neurobehavioral changes. Furthermore, neuroimaging captured before and after the intervention may detect changes resulting from 3MDR.

In addition, increasing the use of narrative approaches, which may include videos, could be implemented to facilitate the impact of the patient’s story. Through tailored immersion, other sensory systems could be integrated into the new 3MDR system to include smells, tactile feedback, environmental sounds, and integration of vestibular and other senses, in addition to visual stimuli. In addition, studies examining the effectiveness of combined treatments to improve the rehabilitation process and timelines should be explored. The consideration of individual and group 3MDR sessions is also worthy of exploration.

Although military members and veterans continue to exhibit higher rates of PTSD because of their increased exposure to combat and other traumatic scenarios, the effects of PTSD, moral injury, and other occupational stress injuries that continue to disrupt the health, well-being, and quality of life of populations affected by trauma require immediate attention. As an exposure-based, VR-supported therapy, 3MDR is currently being used to treat military members and veterans with TR-PTSD. As this paper has demonstrated, there is both an interest in and a need to adapt the intervention for other populations affected by trauma and improve accessibility to treatment. The aim of this initiative was to enhance the mobility, accessibility, feasibility, and applicability of 3MDR for use with other populations affected by trauma. The resulting hardware and software innovation from this initiative was demonstrated to have some level of construct and face validity and will now be used in further clinical trials of 3MDR with PSP who have been affected by trauma related to the COVID-19 pandemic.

As novel interventions for trauma involving VR and AR may change the traditional therapeutic constellation in the near future, it is of utmost importance to investigate their potential to reduce the symptoms of PTSD and increase the quality of life, daily functioning, and safety of populations affected by trauma, as well as that of their families, wider organizations, and communities. As 3MDR continues to emerge in the literature and shows promise, international efforts are positioning 3MDR for more widespread adoption as a potential first-line treatment for PTSD to add to evidence-based trauma treatments. This has involved the current initiative, which focused on hardware development, software optimization, and validation, as well as facilitation of the adoption of 3MDR in mental health clinics, 3MDR therapist training and certification, and new research directions.

Efforts to evolve and advance 3MDR by further improving mobility, accessibility, feasibility, and applicability will continue to be explored with the goal of continuing to adapt to changing technology, as well as the needs of stakeholders, especially populations affected by trauma.