The aim of this clinical trial is to examine how caffeine and L-theanine, taken alone or together, affect both physical and cognitive performance in healthy, trained athletes. The study aims to answer whether these commonly consumed dietary ingredients can enhance strength, endurance, and hand-eye coordination under controlled laboratory conditions. Researchers will compare four supplementation conditions: Caffeine (CAF) - 3 mg per kilogram of body weight L-Theanine (THE) - 200 mg Combined Caffeine and L-Theanine (COM) - same doses together Placebo (CON) - mannitol (inactive substance) Each participant will complete all four test sessions in a randomized, double-blind, crossover design, with at least 72 hours between sessions. Capsules will be taken 60 minutes before testing to allow time for absorption. During each session, participants will perform a series of physical and cognitive tasks, including maximal isometric strength tests, an intermittent endurance test, and a computerized eye-hand coordination task. The main hypothesis is that caffeine and L-theanine, alone or in combination, will improve strength and cognitive coordination compared with placebo. All participants are healthy competitive athletes between 18 and 30 years old. The study is conducted under standardized laboratory and indoor sports-hall conditions, with ethics approval obtained from the Sinop University Human Research Ethics Committee (Approval No. 2025/337).
Age range
18 Years – 30 Years
Sex
ALL
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The trial coordinator is the person who runs the study day to day. These cover the practical side — logistics, costs, and what taking part would actually mean for your life. The study team confirms whether you meet the criteria; these are questions to ask, not a sign you qualify.
A starting point for the conversation — always confirm anything about your own eligibility, costs, and care with the study team and your doctor.
Total Distance Covered in the Yo-Yo Intermittent Endurance Test Level 1 (meters)
Timeframe: 60 minutes post-supplement ingestion.
Peak Handgrip Force (kgf)
Timeframe: 60 minutes post-supplement ingestion.
Peak Back Extension Force (kgf)
Timeframe: 60 minutes post-supplement ingestion.
Peak Leg Extension Force (kgf)
Timeframe: 60 minutes post-supplement ingestion.
Eye-Hand Coordination Accuracy (EHC-A)
Timeframe: 60 minutes post-supplement ingestion.
Eye-Hand Coordination Fast Speed Reaction Time (EHC-FS)
Timeframe: 60 minutes post-supplement ingestion.
Eye-Hand Coordination Slow Speed Reaction Time (EHC-SS)
Timeframe: 60 minutes post-supplement ingestion.
Eye-Hand Coordination Distance From Ball Center (EHC-DFBC)
Timeframe: 60 minutes post-supplement ingestion.