Effects of Caffeine on Agility in Amateur Soccer Players

Healthy Adult Male

Caffeine, Athletes, Exercise, Muscle Strength, Psychomotor Performance

This randomized, double-blind, placebo-controlled crossover clinical trial aims to investigate the acute effects of caffeine supplementation on motor and perceptual-cognitive components of agility performance in male amateur soccer players. The main questions are: i) Does acute caffeine supplementation improve motor performance, including countermovement jump height, drop-jump reactive strength, and planned agility? ii) Does acute caffeine supplementation improve perceptual-cognitive performance during reactive agility tasks involving light and human stimuli? Participants will complete two experimental conditions in randomized order, receiving either 300 mg of caffeine (\ 3.7 miligrams/kilograms of body mass) or placebo pills. Following ingestion, participants will perform countermovement and drop jumps and three Y-shaped agility tests assessing planned agility, reactive agility to a light stimulus, and reactive agility to a human stimulus.

Caffeine supplementation was investigated for its potential to differentially affect motor and perceptual-cognitive aspects of performance in athletes. Participants were recruited from amateur soccer clubs competing in the third to fifth tiers of the Slovak league system and fifth to sixth tiers of the Austrian league system. A pre-selection questionnaire was used to assess relevant demographic, sporting, health, injury, and habitual caffeine consumption characteristics. Players with habitual caffeine intake above 400 miligrams/day were excluded. A familiarization session was conducted approximately one week before the experimental measurements to practice the procedures and reduce learning effects. The intervention consisted of a single 300 milligrams caffeine dose, corresponding to approximately 3.7 miligrams/kilograms of body mass. The placebo consisted of potato starch. Caffeine and placebo capsules were visually identical. Condition order was determined by simple randomization using an independent online randomization generator, and the investigator responsible for randomization was not involved in testing. Participants and testers remained unaware of the assigned condition. Participants were instructed to maintain their usual training regimen, abstain from caffeine-containing products for at least 24 hours before testing, and avoid intense physical activity on the preceding day. The two experimental sessions were conducted seven days apart, during the same period of the soccer season and at the same time of day to reduce potential effects of recovery and circadian variation. Diet, fluid intake, and sleep were not standardized. After capsule ingestion, participants completed a standardized dynamic warm-up involving aerobic activation, lunges, dynamic stretching, and countermovement jumps. Testing subsequently assessed explosive lower-limb performance and agility under controlled laboratory and field conditions. The agility assessment used a Y-shaped setup and distinguished between a predetermined change-of-direction task and reactive tasks requiring a response to either a visual light stimulus or a live human stimulus. The human-stimulus condition was designed to introduce a greater perceptual and decision-making component than the planned condition. Participants were required to perceive the tester's movement and rapidly select the appropriate alternative direction. Reactive trials were repeated when predefined technical errors, incorrect responses, slips, or other invalid performances occurred. The experimental procedures were completed within a short testing window following supplementation to correspond with the expected onset of caffeine's acute physiological effects. The fixed testing sequence was maintained across both experimental conditions to ensure consistency between visits. The study was conducted in accordance with the Declaration of Helsinki and was approved by the Ethics Committee of the Faculty of Physical Education and Sport, Comenius University in Bratislava (Approval Number 15/2024). All participants provided written informed consent before participation.

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