Effects of Virtual Reality Environments on Walking in Adults With and Without Knee Osteoarthritis

All participants, including individuals with knee osteoarthritis and healthy controls, complete five walking conditions: (1) walking without virtual reality (VR), (2) walking in a neutral VR environment, (3) walking in a safety-promoting VR environment on low ground, (4) walking in a fear-inducing VR environment, and (5) walking in a safety-promoting VR environment on high ground. Participants walk along a straight 6-meter walkway at a self-selected comfortable speed, with at least five valid walking trials per condition whenever feasible. Gait biomechanics and subjective responses are assessed across all conditions.

Participants perform repeated walking trials in four immersive virtual reality (VR) environments presented through a head-mounted display (Vive Focus 3): (1) a neutral environment, (2) a safety-promoting environment on low ground, (3) a fear-inducing environment, and (4) a safety-promoting environment on high ground. Each condition involves walking along a straight 6-meter walkway at a self-selected comfortable speed. At least five valid trials are collected per condition whenever feasible, with a minimum of three valid trials accepted if limited by pain, fatigue, or VR discomfort. The environments are designed to manipulate perceived safety and fear during walking.

Participants perform overground walking without a virtual reality headset along a straight 6-meter walkway at a self-selected comfortable speed. At least five valid walking trials are collected whenever feasible, with a minimum of three valid trials accepted if limited by pain or fatigue. This condition serves as the control for comparison with the four immersive VR walking conditions.

Mean gait speed (m/s) during overground walking, measured using the Xsens MVN Awinda inertial motion capture system. Gait speed will be calculated as the average across valid walking trials for each of the five experimental conditions (one non-VR and four VR conditions).

Cadence (steps/min) measured using the Xsens MVN Awinda inertial motion capture system. Mean cadence will be calculated across valid walking trials for each of the five experimental conditions.

Mean stride length (m), defined as the distance covered during one complete stride, measured using the Xsens MVN Awinda inertial motion capture system and averaged across valid trials in each walking condition.

Mean stride time (s), defined as the duration of one complete gait cycle, measured using the Xsens MVN Awinda inertial motion capture system and averaged across valid trials in each walking condition.

Mean step width (m), defined as the mediolateral distance between the feet during walking, measured using the Xsens MVN Awinda inertial motion capture system and averaged across valid trials in each walking condition.

Mean stance phase duration, expressed as a percentage of the gait cycle (%), measured using the Xsens MVN Awinda inertial motion capture system and averaged across valid trials in each walking condition.

Mean swing phase duration, expressed as a percentage of the gait cycle (%), measured using the Xsens MVN Awinda inertial motion capture system and averaged across valid trials in each walking condition.

Mean double support duration, expressed as a percentage of the gait cycle (%), measured using the Xsens MVN Awinda inertial motion capture system and averaged across valid trials in each walking condition.

First vertical ground reaction force peak during weight acceptance, measured using force platforms, normalized to body weight, and averaged across valid trials in each walking condition.

Second vertical ground reaction force peak during push-off, measured using force platforms, normalized to body weight, and averaged across valid trials in each walking condition.

Minimum vertical ground reaction force during mid-stance, measured using force platforms, normalized to body weight, and averaged across valid trials in each walking condition.

Hip flexion-extension range of motion during walking, expressed in degrees, measured using the Xsens MVN Awinda inertial motion capture system and averaged across valid trials in each walking condition.

Knee flexion-extension range of motion during walking, expressed in degrees, measured using the Xsens MVN Awinda inertial motion capture system and averaged across valid trials in each walking condition.

Ankle dorsiflexion-plantarflexion range of motion during walking, expressed in degrees, measured using the Xsens MVN Awinda inertial motion capture system and averaged across valid trials in each walking condition.

Variability in step time during walking, assessed using the Xsens MVN Awinda inertial motion capture system and expressed as the coefficient of variation (%). Variability is calculated across consecutive steps within each experimental condition.

Variability in stance phase duration during walking, assessed using the Xsens MVN Awinda inertial motion capture system. Variability is calculated across consecutive gait cycles within each experimental condition.

Variability in the mediolateral distance between the feet during walking, assessed using the Xsens MVN Awinda inertial motion capture system across consecutive steps within each experimental condition.

Left-right symmetry of gait, assessed using inertial motion capture and/or ground reaction force data. The index represents differences between the lower limbs in loading or stance time across experimental conditions.

Pain intensity is assessed in participants with knee osteoarthritis using an 11-point Numeric Rating Scale (NRS), ranging from 0 (no pain) to 10 (worst imaginable pain). Participants rate their pain after each of the five walking conditions.

Perceived fear and safety during walking are assessed using a custom questionnaire after each of the five walking conditions in participants with knee osteoarthritis and healthy controls. Perceived fear is rated on a 7-point scale ranging from 1 (no fear at all) to 7 (extreme fear), with higher scores indicating greater fear (a worse outcome). Perceived safety is rated on a separate 7-point scale ranging from 1 (not at all safe) to 7 (completely safe), with higher scores indicating greater perceived safety (a better outcome). The two ratings are reported separately and are not combined into a total score.

Movement-related fear is assessed in participants with knee osteoarthritis using the 17-item Tampa Scale for Kinesiophobia (TSK-17). The questionnaire evaluates fear of movement and reinjury associated with physical activity. Total scores range from 17 to 68, with higher scores indicating greater kinesiophobia (a worse outcome).

Health-related quality of life is assessed in participants with knee osteoarthritis using the 36-Item Short Form Health Survey (SF-36). The questionnaire evaluates eight domains of physical and mental health. Each domain is scored from 0 to 100, with higher scores indicating better health-related quality of life.

The subjective sense of presence within the virtual environment is assessed using the 14-item Igroup Presence Questionnaire (IPQ) after each of the four immersive VR walking conditions. The questionnaire assesses spatial presence, involvement, and experienced realism, with an additional item assessing general presence. Items are rated on a 7-point scale from -3 to +3. After appropriate reverse coding, mean subscale scores and the general presence item score range from -3 to +3, with higher scores indicating a stronger sense of presence in the virtual environment.

The subjective level of immersion in the virtual environment is assessed using a 3-point immersion rating scale adapted from Cole et al. after each of the four immersive VR walking conditions. Scores range from 1 to 3: 1 indicates awareness of the technology, 2 indicates partial awareness of the technology and a feeling of being inside the virtual environment, and 3 indicates complete virtual immersion. Higher scores indicate greater subjective immersion.

Symptoms associated with virtual reality exposure are assessed using the 9-item Virtual Reality Sickness Questionnaire (VRSQ) before the VR walking conditions and immediately after completion of the final VR condition. Each symptom is rated from 0 (none) to 3 (severe). The total score is calculated as the average of the oculomotor and disorientation subscale scores, each standardized to a range of 0-100. Total scores range from 0 to 100, with higher scores indicating more severe virtual reality sickness symptoms (a worse outcome).