Mental fatigue (MF) is known to impair cognitive performance and may negatively affect physical performance. While its effects on lower-extremity functional performance have been investigated, little is known about the influence of MF on upper-extremity physical performance tests commonly used in sports and rehabilitation settings. This randomized crossover study will investigate the effects of experimentally induced mental fatigue on upper-extremity physical performance in 16 healthy physically active adults. Participants will complete both a mental fatigue condition, involving a prolonged Stroop task, and a control condition consisting of watching an emotionally neutral documentary. Before and after each condition, participants will perform the Upper Quarter Y Balance Test, Reactive Upper Quarter Y Balance Test, Closed Kinetic Chain Upper Extremity Stability Test, and Seated Single-Arm Shot Put Test. Subjective mental fatigue, cognitive performance, motivation, and perceived exertion will also be assessed. The findings will improve understanding of whether mental fatigue influences upper-extremity physical performance test outcomes and may assist clinicians and researchers in interpreting these assessments in sports medicine and rehabilitation contexts.

Inclusion Criteria:

• Age between 18 and 35 years
• Healthy (no neurological, cardiovascular or musculoskeletal disorders of any kind)
• Male or female
• No prior knowledge of the concept of mental fatigue
• Not currently taking medications that affect cognition or neuromuscular performance
• According to the International Physical Activity Questionnaire, being physically active at a minimum level of 1500 MET-min/week

Exclusion Criteria:

• Previous major upper limb injury (last 6 months)
• Involvement in another concurrent physical or cognitive intervention study
• Use of caffeine and heavy efforts 24 hours prior each trial
• Suffering from colour vision deficiencies
• Not eating a standardized meal, the morning of each trial and the evening before each trial

De-identified individual participant data (IPD) will be shared upon reasonable request. This includes baseline characteristics, intervention allocation, and all primary and secondary outcome measures (upper-extremity physical performance test results, cognitive performance data, subjective mental fatigue scores, motivation scores, perceived exertion ratings, and Stroop task performance data). All data will be fully anonymized to protect participant confidentiality. Additional study-related materials such as the study protocol and statistical analysis plan may also be made available. Data will be shared for non-commercial research purposes after publication of the main study results.

IPD and supporting documents will become available beginning 6 months after publication of the primary study results and will remain accessible for a period of 5 years.

De-identified individual participant data (IPD) and supporting study documents will be made available to qualified researchers upon reasonable request for non-commercial use. Requests must include a methodologically sound research proposal and will be reviewed and approved by the principal investigator or study sponsor. Data will be shared under a data-sharing agreement to ensure compliance with ethical and data protection regulations. Access will be provided via secure data transfer platforms or institutional repositories.