The Development of a Virtual Reality-based Training System for Prosthetic Foot Users: Effects on Motion Sickness and Postural Stability

Virtual reality (VR) has been widely used for training purposes, including in prosthetic foot rehabilitation training systems. Using VR, lower-limb amputees can be trained to walk safely in various conditions. However, there are issues related to the potential emergence of motion sickness in VR, which can be an obstacle to adopting this technology. This study aimed to evaluate the incidence of motion sickness in a virtual reality-based prosthetic foot training system. The evaluation utilized heel strike events detected using a Kinect motion capture sensor as an input to move the virtual environment that aimed to synchronize the visual and vestibular movement signals to inhibit motion sickness development. A total of 28 male participants (15 able-bodied and 13 transfemoral amputees) were involved in this study. Participants were asked to walk on a treadmill using a VR HMD for 40 minutes, followed by a 30-minute rest. Every 10 minutes, motion sickness consisting of oculomotor, disorientation, and total motion sickness severity was measured using the virtual reality sickness questionnaire (VRSQ). Furthermore, 12 participants (6 able-bodied and 6 transfemoral amputees) were asked to stand with their eyes closed on an AMTI force plate, and their postural stability was recorded for 20 seconds. Friedman tests were conducted to compare all three subjective motion sickness symptoms data collected from prosthetic and non-disabled users. The results showed that the use of the designed VR system produced no significant differences in oculomotor, disorientation, and total motion sickness severity incidence between prosthetic and non-disabled users. After 40 minutes of the walking task, the VR system induced VR sickness but at a subtle level. ANOVA tests conducted on the center of pressure (COP) data showed that the use of VR induced an increase in postural instability as shown by an increase in mean distance anterior-posterior data. To fully recover from all oculomotor, disorientation, and total motion sickness severity, participants needed to rest for at least 30 minutes. However, resting for 30 minutes was not effective in changing postural stability. After using VR, it is recommended that users, especially transfemoral amputees, still receive safety assistance and are ensured not to engage in any dangerous activities with disturbed posture. The results of this study can be used to determine the duration of training that is safe and comfortable for users in such a VR design.