Background: Motion sickness (MS) is a common syndrome characterized by autonomic and behavioral symptoms, such as nausea and dizziness, resulting from exposure to motion stimuli. Its pathophysiology is closely linked to sensory conflict and postural instability theories. While previous studies suggest that postural control, proprioception, and reaction times are affected in individuals susceptible to MS, there is a lack of comprehensive, comparative research evaluating all these parameters concurrently within the same cohort using standardized methods. Objective: This study aims to systematically measure balance, proprioceptive sensitivity, coordination, and reaction time parameters, and quantitatively analyze their relationship with motion sickness severity. Methodology: In this prospective, cross-sectional study, at least 41 participants aged 18-40 with motion sickness will be recruited. Participants will undergo motion sickness susceptibility and severity grading using the Motion Sickness Susceptibility Questionnaire Short Form (MSSQ-SF) and the Graybiel Scale. Objective assessments will include static and dynamic balance testing (ProKin®), knee joint position sense (Clinometer app), manual dexterity and dynamic balance coordination (Nine-Hole Peg Test, Tandem Walk, Romberg Test), and upper/lower extremity reaction time measurements (BlazePod system).

Inclusion Criteria:

• Individuals aged between 18 and 40 years.
• Diagnosed with motion sickness according to the Motion Sickness -Susceptibility Questionnaire Short Form (MSSQ-SF).
• Normal hearing acuity.
• No history of acute or chronic vestibular disease, other than motion sickness.
• Normal or corrected-to-normal vision.
• Adequate physical capability to fully perform the measurement protocols, including balance, proprioception, coordination, and reaction time tests.

Exclusion Criteria:

• Presence of any physical or orthopedic problem that could interfere with testing.
• History of acute or chronic instability, unsteadiness, or vertigo.
• Severe visual impairment.
• History of prior ear surgery.
• Presence of any neurological condition or disorder.
• History of migraines.
• Current use of medications that could affect balance or vestibular function (e.g., vestibular suppressants, sedatives).
• Use of alcohol or psychoactive substances within the last 48 hours prior to testing.

The study population consists of adult individuals aged between 18 and 40 years who exhibit susceptibility to motion sickness.