Extended Reality Cognitive and Breathing Training With Eye Tracking for Attention and Stress Regulation in Adolescent Basketball Players

This feasibility randomised controlled trial (RCT) was conducted to evaluate the practicality and acceptability of integrating standalone virtual reality (VR) technology into regular basketball training for adolescent athletes. The study was designed to inform the design and sample size of a future full-scale RCT, and was not powered to confirm intervention effectiveness.

The study used a three-arm parallel-group design. Participants were randomly assigned to one of two experimental extended reality (XR) intervention groups (Cognitive XR or Breathing XR) or to a control group. Randomisation was performed at the individual level. The intervention period lasted six weeks, with two sessions per week for both experimental groups. Control participants continued their regular basketball training without any additional intervention.

All study activities were conducted at participants' existing basketball training venues in Latvia (Ventspils Basketball Arena and Jūrmala Sport School Basketball Arena). Interventions were delivered using the HTC VIVE Focus Vision standalone head-mounted display, requiring no external equipment or PC connection.

Assessments were conducted at two time points: at baseline (before the intervention period) and post-intervention (within one week of the final session). The assessment battery included resting heart rate and heart rate variability (Polar H10 chest strap with KubiosHRV), CO₂ Tolerance Test (CO₂TT), breathing pattern (Hi-Lo test), reactive stress tolerance (Vienna Test System - Determination Test), d2-R Test of Attention (Revised), and pre-competition anxiety test Competitive State Anxiety Inventory-2 Revised (the Latvian-adapted version CSAI-2R-LV).

Research staff supervised the pre-intervention assessment phase and the first two intervention sessions in person. From week two onward, participants accessed sessions independently using individual password-protected profiles on the headset. A midpoint visit was conducted at week three. A minimum adherence threshold of four completed sessions was required for inclusion in the primary analysis, with regularity criteria also applied.

The study was approved by the Riga Stradiņš University Ethics Committee (original approval: 2-PĒK-4/610/2024; additional approvals covering extended details: 2-PĒK-4/814/2025 and 2-PĒK-4/1205/2025). An Open Science Framework (OSF) project page describing the study was created prior to enrollment (osf.io/8sx3r).

• Cognitive XR (Behavioral): Participants complete two 10-minute sessions weekly for 6 weeks (maximum 12 sessions; 120 minutes total exposure) using an HTC VIVE Focus Vision standalone head-mounted display with binocular eye tracking. While dribbling a real basketball, participants follow a moving virtual basketball with their gaze, avoid virtual obstacles, and respond to spatial and auditory cues within predefined court boundaries. Attention time is recorded when a valid gaze signal intersects the active target under the required spatial conditions. Difficulty progresses through target speed, obstacle number and movement, target switching, movement zones, whistle-controlled tasks, jumping obstacles, and spatialized sounds. A fixed pre-programmed level sequence is individually paced according to an on-target-time criterion. Research staff supervise baseline testing and the first two sessions; from week 2, participants use password-protected individual profiles independently.
• Breathing XR (Behavioral): Participants complete two 7-minute sessions weekly for 6 weeks (maximum 12 sessions; 84 minutes total exposure) using an HTC VIVE Focus Vision standalone head-mounted display. Seated within an approximately 1 × 1 m area, participants perform slow diaphragmatic breathing while completing a gaze-controlled virtual basketball-tracking task. Breathing pace progresses from 7 breaths/min in minute 1, to 6.5 breaths/min in minute 2, and 6 breaths/min during minutes 3-7, using a 40:60 inhalation-to-exhalation ratio. A handheld controller placed horizontally on the upper abdomen detects abdominal movement to estimate breathing phase and adherence. Accurate breathing increases virtual-player responsiveness and speed, whereas departures from the prescribed pattern reduce performance. Research staff supervise baseline testing and the first two sessions; from week 2, participants use password-protected individual profiles independently.

Primary outcomes

• Recruitment rate [During recruitment, up to 6 weeks]: Proportion of eligible athletes who provide consent and are enrolled in the study. Reported as the number enrolled divided by the number eligible.
• Randomization completion rate [At baseline, before intervention initiation]: Proportion of enrolled participants who are successfully allocated to one of the study arms. Reported as the number randomized divided by the number enrolled.
• Retention rate [Baseline through 6-week post-intervention assessment]: Proportion of enrolled participants who complete the post-intervention assessment. Reported as the number completing follow-up divided by the number enrolled.
• Intervention adherence [During the 6-week intervention period]: Attendance among participants allocated to either XR intervention arm. Reported as the number of intervention sessions completed out of 12 scheduled sessions, expressed as a percentage.
• Intervention acceptability [At 6 weeks (post-intervention)]: Post-intervention acceptability assessed using a study-specific 4-item questionnaire measuring task interest, mixed-reality excitement, motivation to perform tasks, and willingness to continue. Items are rated from 1 (completely disagree) to 5 (completely agree). Total score range: 4 (minimum) to 20 (maximum). Higher scores indicate greater acceptability. Report item scores and/or mean total score.

Secondary outcomes

• Selective attention - concentration performance level (d2-R SUMKL) [Baseline and 6 weeks]: Selective attention was assessed using the d2-R Test of Attention (d2-R). The SUMKL score represents total concentration performance level across all 14 test rows, calculated as the number of correctly cancelled target items minus total errors (higher scores indicate better selective attention). Block-specific indices B1KL-B4KL, reflecting concentration performance in rows 1-4 respectively, were also analyzed. Scores are calculated according to standardized d2-R scoring procedures.
• Sustained attention and processing speed - total correctly processed items (d2-R SUMBZO) [Baseline and 6 weeks]: Sustained attention and processing speed were assessed using the d2-R Test of Attention (d2-R). The SUMBZO score represents the total number of correctly processed items across all 14 test rows, reflecting the speed and quantity of attentional processing sustained over the full test duration (higher scores indicate better performance). Block-specific indices B1BZO-B4BZO, reflecting correctly processed items in rows 1-4 respectively, were also analyzed. Scores are calculated according to standardized d2-R scoring procedures.
• Omission errors - failures to mark target stimuli (d2-R SUMAF) [Baseline and 6 weeks]: Omission errors were assessed using the d2-R Test of Attention (d2-R). The SUMAF score represents the total number of omission errors (failures) across all 14 test rows - instances where a target stimulus (a letter "d" with exactly two dashes) was not marked within the allotted time. Block-specific index B2AF, reflecting omission errors in row 2, was also analyzed. Lower scores indicate better performance. Scores are calculated according to standardized d2-R scoring procedures.
• Commission errors - false responses (d2-R SUMVF) [Baseline and 6 weeks]: Commission errors (false responses) were assessed using the d2-R Test of Attention (d2-R). The SUMVF score represents the total number of false responses - non-target stimuli that were incorrectly cancelled - across all 14 test rows. Lower scores indicate better performance (fewer false responses). Scores are calculated according to standardized d2-R scoring procedures.
• Change from Baseline to 6 Weeks in Functional Breathing Pattern Proportion [Baseline and 6 weeks]: Assessment of resting breathing pattern evaluated using the Hi-Lo Breathing Assessment (Hi-Lo). Participants are classified categorically as exhibiting a "Functional" (predominantly abdominal/diaphragmatic) or "Dysfunctional" (predominantly thoracic/apical) breathing pattern.
• Change from Baseline to 6 Weeks in Carbon Dioxide Tolerance Test (CO2TT) Exhalation Duration [Baseline and 6 weeks]: Exhalation duration in seconds measured using the CO₂ Tolerance Test during seated nasal breathing after a full inhalation. More prolonged exhale signals better CO₂ Tolerance.
• Change from Baseline to 6 Weeks in CSAI-2R Cognitive State Anxiety Subscale Score [Baseline and 6 weeks]: Cognitive state anxiety measured using the 5-item Cognitive Anxiety subscale of the Revised Competitive State Anxiety Inventory-2 (CSAI-2R). Items are rated on a 4-point Likert scale (1 = Not at all to 4 = Very much so). Higher scores indicate greater cognitive state anxiety. Subscale score is obtained by summing, dividing by number of items, and multiplying by 10. Score range is 10 to 40 for each subscale.
• Change from Baseline to 6 Weeks in CSAI-2R Somatic State Anxiety Subscale Score [Baseline and 6 weeks]: Somatic state anxiety measured using the 7-item Somatic Anxiety subscale of the CSAI-2R. Items are rated on a 4-point Likert scale (1 = Not at all to 4 = Very much so). Higher scores indicate greater physical/somatic anxiety symptoms. Subscale score is obtained by summing, dividing by number of items, and multiplying by 10. Score range is 10 to 40 for each subscale.
• Change from Baseline to 6 Weeks in CSAI-2R Self-Confidence Subscale Score [Baseline and 6 weeks]: Sport self-confidence measured using the 5-item Self-Confidence subscale of the CSAI-2R. Items are rated on a 4-point Likert scale (1 = Not at all to 4 = Very much so). Higher scores indicate greater competitive self-confidence. Subscale score is obtained by summing, dividing by number of items, and multiplying by 10. Score range is 10 to 40 for each subscale.
• Change from Baseline to 6 Weeks in Resting Heart Rate [Baseline and 6 weeks]: Resting heart rate recorded in beats per minute (bpm) using a Polar H10 chest strap during a 3-minute supine morning recording, averaged across three consecutive days. Measured via Kubios HRV software. Lower heart rate reflects enhanced cardiovascular resting status.
• Change from Baseline to 6 Weeks in Resting Heart Rate Variability RMSSD [Baseline and 6 weeks]: Parasympathetic autonomic activity measured as the Root Mean Square of Successive Differences (RMSSD) between normal heartbeats, expressed in milliseconds (ms). Recorded via a Polar H10 chest strap in a supine position over 3 minutes on three consecutive mornings and processed using Kubios HRV software. Higher RMSSD values indicate greater vagal tone and stress recovery capacity.
• Change from Baseline to 6 Weeks in Resting Heart Rate Variability SDNN [Baseline and 6 weeks]: Overall heart rate variability measured as the Standard Deviation of Normal-to-Normal RR intervals (SDNN), expressed in milliseconds (ms). Recorded via a Polar H10 chest strap during a 3-minute supine morning trial and calculated using Kubios HRV software. Higher SDNN reflects greater overall autonomic flexibility.
• Change from Baseline to 6 Weeks in Resting Heart Rate Variability High-Frequency Power [Baseline and 6 weeks]: Spectral parasympathetic activity measured as High-Frequency power (HF: 0.15-0.40 Hz) in absolute units (ms²). Recorded via a Polar H10 chest strap during a 3-minute supine trial and analyzed via Fast Fourier Transform in Kubios HRV software. Higher HF power indicates enhanced respiratory sinus arrhythmia and vagal modulation.
• Change from Baseline to 6 Weeks in Mean RR Interval [Baseline and 6 weeks]: Mean duration between consecutive cardiac inter-beat intervals (RR intervals), expressed in milliseconds (ms). Recorded via a Polar H10 chest strap during a 3-minute supine resting condition and calculated via Kubios HRV software.
• Change from Baseline to 6 Weeks in Resting Respiratory Rate [Baseline and 6 weeks]: Resting breathing frequency derived from electrocardiogram (ECG)-based chest strap (Polar H10) oscillations (ECG-derived respiration) in Kubios HRV software during a 3-minute resting supine trial, expressed in breaths per minute. Lower resting respiratory rates reflect more efficient resting ventilatory patterns.
• Change from Baseline to 6 Weeks in Determination Test Correct Responses [Baseline and 6 weeks]: Reactive stress tolerance performance evaluated via the Vienna Test System Determination Test, Form S1 (a standard adaptive test protocol). Measured as the total count of correct motor responses executed in response to rapid color, acoustic, and spatial stimuli during the adaptive test module. Higher counts indicate superior stress tolerance and response accuracy under pressure.
• Change from Baseline to 6 Weeks in Determination Test Median Reaction Time [Baseline and 6 weeks]: Processing speed under stress evaluated via the Vienna Test System Determination Test (Form S1). Measured as the median reaction time in milliseconds (ms) across all correct responses during the stimulus presentation phase. Lower reaction times indicate faster sensorimotor processing.

Sex: All, ages: 14 Years to 17 Years, accepts healthy volunteers

Inclusion criteria

* Adolescent basketball players aged 14-17 years
* Organized basketball training for at least 5 years
* Training at least 3 times per week

Exclusion criteria

* Serious musculoskeletal injury or acute medical condition affecting sports performance in the previous month
* Severe orthopedic, neurological, cardiovascular, or other medical disorders
* Use of prescription medications affecting the central nervous system (e.g., psychotropic medication)
* Symptoms of visually induced motion sickness (VIMS): nausea, dizziness, headache, or disorientation before or during participation

• Agris Liepa, PhD, Study director, Riga Stradins University