This study investigates how different doses of caffeine affect physical and cognitive performance in female handball players. Caffeine is widely used as a performance-enhancing substance, but its effects may vary depending on the type of performance and the dose consumed.

In this randomized, double-blind, placebo-controlled crossover study, participants complete three experimental conditions: placebo, low-dose caffeine (3 mg/kg), and moderate-dose caffeine (6 mg/kg). Each participant receives all conditions in a randomized order, with sufficient time between sessions to avoid carryover effects.

The study evaluates three main performance domains relevant to team sports. Physical performance is assessed using an intermittent running test. Cognitive performance is measured using a reaction time task that evaluates attention and inhibitory control. In addition, a throwing test is used to assess sport-specific motor performance.

The main objective is to determine whether caffeine produces dose-dependent improvements and whether these effects differ across physical, cognitive, and technical performance domains. The findings aim to provide practical insights for athletes and coaches regarding optimal caffeine use in team sport settings.

Caffeine is one of the most widely consumed ergogenic aids in sport, known to influence both physiological and cognitive processes primarily through antagonism of adenosine receptors. Although its beneficial effects on endurance performance and alertness are well established, evidence regarding its effects on cognitive control and sport-specific technical skills remains inconsistent, particularly in team sport settings where multiple performance domains interact.

Team sports such as handball require the integration of intermittent high-intensity physical efforts, rapid decision-making, and precise motor execution. These components are not independent; instead, they compete for shared neurocognitive resources, especially under conditions of fatigue. As a result, interventions such as caffeine supplementation may exert domain-specific effects rather than uniform improvements across all aspects of performance.

Despite extensive research on caffeine, most studies have examined either physical or cognitive outcomes in isolation. Furthermore, dose-response relationships remain unclear, with previous findings suggesting that lower doses may be sufficient to enhance physical performance, whereas cognitive outcomes may require higher levels of stimulation. However, limited evidence exists on whether these dose-dependent effects are maintained when multiple performance domains are assessed within the same experimental framework.

The present study addresses this gap by simultaneously evaluating physical, cognitive, and sport-specific motor performance following different doses of caffeine in female handball players. A randomized, double-blind, placebo-controlled crossover design is used to minimize inter-individual variability and improve internal validity. Participants complete three experimental conditions (placebo, low-dose caffeine, and moderate-dose caffeine), each separated by an adequate washout period to reduce potential carryover effects.

The protocol includes standardized procedures to control for confounding factors such as time of day, environmental conditions, and prior physical activity. Testing sessions follow a fixed sequence, beginning with cognitive assessment, followed by a sport-specific throwing task, and concluding with an intermittent running test. This structure is designed to reflect the multi-component demands of team sport performance while maintaining methodological control.

The primary objective is to determine whether caffeine produces dose-dependent effects across different performance domains. Specifically, the study examines whether physical performance improvements occur at lower doses, whether cognitive performance shows greater sensitivity to higher doses, and whether technical motor performance responds differently to caffeine ingestion. By integrating these domains within a single experimental design, the study aims to provide a more ecologically valid understanding of caffeine's ergogenic effects in team sport contexts.

The findings are expected to contribute to evidence-based recommendations for caffeine use in athletes, emphasizing the importance of aligning supplementation strategies with specific performance goals rather than assuming uniform benefits across all domains.

Inclusion Criteria:

• Female handball players
• Regular participation in competitive handball training
• Minimum of 3 years of handball training experience
• Free from musculoskeletal injury within the past 6 months

Exclusion Criteria:

• Known caffeine sensitivity or allergy
• Use of medications or supplements that may affect physical or cognitive performance
• Presence of cardiovascular disease
• Presence of metabolic disorders

At the time of registration, a decision regarding sharing individual participant data (IPD) has not yet been finalized. The study dataset is currently being prepared for publication and institutional archiving. Future data sharing will be considered after publication, taking into account institutional policies, ethical approvals, and participant confidentiality requirements. If appropriate, de-identified data underlying the published results may be made available upon reasonable request.