Effects of Caffeine on Physical and Perceptual-cognitive Components of Agility in Amateur Soccer Players

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.