Lower extremity muscle strength is a fundamental determinant of an individual's ability to maintain functional mobility, preserve balance, and perform activities of daily living independently. One of the methods used for the comprehensive evaluation of these functions is the Five-Repetition Sit-to-Stand (5STS) test, which is considered an effective tool for assessing lower extremity strength, balance, and functional mobility in both healthy individuals and various clinical populations. In this test, participants are required to consecutively stand up from and sit down on a chair five times without using their arms, and the completion time is recorded in seconds to objectively evaluate functional capacity. Due to its simplicity, low cost, and high reliability, the 5STS test is widely used in clinical and research settings.

However, functional tests administered in conventional clinical environments may be insufficiently standardized due to factors such as examiner-related variability, measurement errors, and environmental influences. This limitation makes it difficult to detect small performance differences and restricts test repeatability. In recent years, rapidly advancing virtual reality (VR) technology has contributed to overcoming these limitations by offering the potential to digitally standardize measurement processes. VR systems, which recreate real-life scenarios in a three-dimensional and interactive manner, allow for a more comprehensive and objective assessment of motor performance. In addition, by increasing user interaction and reducing observer-related errors, VR enhances clinical validity. One study has reported that the most important advantage of VR in clinical balance assessments is its ability to provide a fully controllable, repeatable, and standardized environment. Similarly, a systematic review found that VR-based exercises resulted in significant improvements in motor skills, balance, and cognitive function, while increasing user engagement and motivation and thereby contributing to more effective rehabilitation outcomes.

Current literature indicates that VR technology is increasingly being utilized in physiotherapy and exercise sciences. In one study, the validity and feasibility of a VR adaptation of the Wingate Anaerobic Test were investigated, and it was reported that the VR version produced performance outcomes comparable to the conventional test, while participant satisfaction was significantly higher with the VR-based method. Likewise, another study demonstrated that the VR adaptation of the Six-Minute Pegboard and Ring Test exhibited high levels of validity and reliability. Together, these studies indicate that VR-based functional tests are both feasible and clinically consistent.

Despite this, no studies to date have examined the validity and reliability of the Five-Repetition Sit-to-Stand test in an immersive VR environment for assessing lower extremity function. Therefore, the present study aims to determine the validity, reliability, and feasibility of a virtual reality-based Five-Repetition Sit-to-Stand test (5STS-VR) developed on the Meta Quest 3 platform in asymptomatic young adults. Additionally, convergent validity will be evaluated by analyzing the relationships between performance data obtained from the virtual environment and outcomes of the Y-Balance Test and lower extremity muscle strength measurements.

Inclusion Criteria:

• Aged between 18 and 30 years,
• Asymptomatic, with no neurological, cardiovascular, or musculoskeletal symptoms,
• Ability to perform activities of daily living independently,
• Visual, auditory, and vestibular functions adequate for virtual reality applications,
• Ability to understand and follow instructions in Turkish,
• Willingness to participate voluntarily in the study.

Exclusion Criteria:

• History of lower extremity injury, surgical procedure, or serious musculoskeletal condition within the past six months,
• Presence of vestibular disorders, balance impairment, or visual or hearing impairments,
• Experiencing symptoms of VR sickness, such as dizziness, nausea, or spatial disorientation during virtual reality applications,
• Diagnosis of neurological, cardiovascular, or metabolic disease,
• Engaging in intensive exercise or being a professional athlete,
• Insufficient cognitive ability to understand test instructions,
• Voluntary withdrawal from the study during the research process.

Asymptomatic young adults aged 18-30 years who are able to perform activities of daily living independently and have no neurological, cardiovascular, or musculoskeletal conditions affecting functional performance.