Effects of Virtual Reality-Based Optokinetic Stimulation on Landing Technique and Dynamic Knee Valgus in Athletes

This two-arm, parallel-group, assessor-blinded randomized controlled study will investigate the immediate and one-week retention effects of virtual reality-based optokinetic stimulation added to drop vertical jump training.

Before randomization, all candidates will complete a five-minute virtual reality familiarization session. System usability and simulator sickness symptoms will be assessed to determine eligibility. Twenty eligible athletes will be randomly allocated to jump-landing training alone or the same training supplemented with virtual reality-based optokinetic stimulation.

Both groups will complete a standardized warm-up and task familiarization, followed by baseline assessment. Training will consist of two blocks of 10 drop vertical jumps from a 30-cm box toward a target positioned at a distance equal to 50% of the participant's height. Participants will rest for 30 seconds between repetitions and five minutes between training blocks. Performance feedback based on landing errors will be provided after each block.

In the experimental group, optokinetic stimulation will be delivered using a Meta Quest 3S headset while participants sit in a supported chair with their feet on the floor. A custom virtual environment will display moving balloons against a sky background. Participants will track a red target balloon with their eyes while keeping their head as still as possible. Foreground stimuli will move at 30 degrees per second, with the background moving in the opposite direction at twice that speed. Before each training block, participants will receive three 60-second exposures in each direction, providing six minutes of active stimulation per block and 12 minutes across the session, excluding rest periods. The headset will be removed before jump training.

The primary outcome will be landing technique assessed using the Landing Error Scoring System from frontal and sagittal video recordings. The secondary outcome will be the frontal plane projection angle during single-leg squatting, calculated as the mean of three successful repetitions at the deepest squat position. Both outcomes will be assessed at baseline, after training, and at a one-week retention visit by an assessor blinded to group allocation. Post-training and retention assessments will be performed without additional corrective instructions or performance feedback.

Simulator sickness symptoms will be monitored in the virtual reality group. Stimulation will be stopped if moderate or severe symptoms occur, safe continuation is not possible, or the participant wishes to stop. The System Usability Scale will be used for eligibility screening, and the Simulator Sickness Questionnaire will be used for tolerability screening and symptom monitoring; neither will be treated as an efficacy outcome.

Participants will complete a single session of drop vertical jump training consisting of two blocks of 10 repetitions, with 30 seconds of rest between repetitions and five minutes between blocks. Performance feedback will be provided after each block. Seated virtual reality-based optokinetic stimulation will be administered before each training block, consisting of three 60-second exposures in each direction, totaling six minutes of active stimulation per block

Behavioral: Drop Vertical Jump Training · Device: Virtual Reality-Based Optokinetic Stimulation

Participants will complete the same single-session drop vertical jump training as the experimental group, consisting of two blocks of 10 repetitions, with 30 seconds of rest between repetitions and five minutes between blocks. Performance feedback will be provided after each block. No additional optokinetic stimulation will be administered before the training blocks.

Behavioral: Drop Vertical Jump Training

Following a standardized warm-up and task familiarization, participants will perform two blocks of 10 drop vertical jumps from a 30-cm box toward a target positioned at 50% of their height. After landing on both feet, participants will immediately jump as high and forward as possible and maintain the final landing position for five seconds. Rest periods will be 30 seconds between repetitions and five minutes between blocks. Feedback based on real-time landing error scores will be provided after each block.

Optokinetic stimulation will be delivered through a Meta Quest 3S headset while participants sit in a supported chair with their feet on the floor. Participants will track a red balloon with their eyes while keeping their head as still as possible. Foreground stimuli will move at 30 degrees per second, with the background moving in the opposite direction at twice that speed. Three 60-second exposures will be delivered in each direction before each training block, with 30-60-second rest periods. Active stimulation will total six minutes per block and 12 minutes across the session, excluding rest. The headset will be removed before jump training.

Time frame: Baseline (before training), immediately after the training session, and one week after training (retention).

Landing technique will be assessed using the 17-item Landing Error Scoring System (LESS) from frontal and sagittal video recordings of the drop vertical jump task. Total scores range from 0 to 19 points, with higher scores indicating more landing errors and poorer landing technique. Participants will complete five successful trials at each assessment, and the mean total score across these five trials will be used for analysis. Assessments will be performed by an assessor blinded to group allocation. Changes over time will be compared between groups.

Time frame: Baseline (before training), immediately after the training session, and one week after training (retention).

Dynamic knee valgus will be assessed using two-dimensional frontal-plane video analysis during a single-leg squat on the dominant limb. The frontal plane projection angle (FPPA), expressed in degrees, will be measured at the deepest squat position using lines connecting the anterior superior iliac spine, the midpoint of the patella, and the midpoint of the ankle joint. The mean of three successful repetitions will be used for analysis. Changes over time will be compared between groups by an assessor blinded to group allocation.Assessments will be performed by an assessor blinded to group allocation. Changes over time will be compared between groups.

Effects of Optokinetic Stimulation Added to Drop Vertical Jump Training on Landing Error Scores and Dynamic Knee Valgus: An Assessor-Blinded Randomized Controlled Trial