TCP-600 Supplementation and Performance Response in Professional Football Players (TCP600-RESP)

Participants assigned to this arm will receive placebo capsules for 28 consecutive days. Placebo capsules will be matched to the active supplement in appearance, number, packaging, and administration schedule.

Matching placebo capsules administered orally once daily for 28 consecutive days. The placebo was matched to the active supplements in appearance, number, packaging, and administration schedule.

Participants assigned to this arm will receive taurine 1500 mg/day and anhydrous caffeine 200 mg/day, administered orally once daily for 28 consecutive days. Matching placebo capsules will be used to maintain the same total number and appearance of capsules across study arms.

Taurine 1500 mg/day administered orally once daily in capsules for 28 consecutive days.

Anhydrous caffeine 200 mg/day administered orally once daily in capsules for 28 consecutive days.

Participants assigned to this arm will receive a multi-ingredient supplementation protocol containing taurine 1500 mg/day, anhydrous caffeine 200 mg/day, and phosphatidylserine 600 mg/day, administered orally once daily for 28 consecutive days. This intervention is referred to as the TCP-600 protocol.

Taurine 1500 mg/day administered orally once daily in capsules for 28 consecutive days.

Anhydrous caffeine 200 mg/day administered orally once daily in capsules for 28 consecutive days.

Phosphatidylserine 600 mg/day administered orally once daily in capsules for 28 consecutive days.

Proportion of participants classified as multidimensional responders after 28 days of supplementation. A multidimensional responder will be defined as a participant meeting the predefined response criterion in at least two of four domains: physical performance/fatigue resistance, cognitive fatigue-related performance, recovery/readiness, and football-specific perceptual-cognitive performance. The outcome will be reported as the percentage of participants classified as multidimensional responders in each group.

Unit of Measure: percentage of participants

Change in 30 m sprint performance from baseline to post-intervention testing. Sprint time will be measured using electronic timing gates. Participants will perform three maximal 30 m sprint trials separated by standardized recovery periods, and the best valid trial will be used for analysis.

Change in reaction time during the computerized cognitive fatigue task from baseline to post-intervention testing after 28 days of supplementation. Reaction time will be measured during the predefined cognitive task performed under cognitive load. The outcome will be reported as the mean change in reaction time from baseline to post-intervention testing. Lower values indicate faster cognitive responses.

Unit of Measure: milliseconds

Change in perceived mental fatigue from baseline to post-intervention testing after 28 days of supplementation. Perceived mental fatigue will be assessed using a 0-10 visual analogue scale, where 0 indicates no perceived mental fatigue and 10 indicates maximal perceived mental fatigue. The outcome will be reported as the mean change in score from baseline to post-intervention testing. Higher scores indicate greater perceived mental fatigue.

Unit of Measure:

points on a 0-10 scale

Change in heart rate variability from baseline monitoring to the final 3 days of supplementation. Heart rate variability will be expressed as the natural logarithm of the root mean square of successive RR interval differences. Morning HRV will be recorded under standardized resting conditions. The outcome will be reported as the mean change in final 3-day mean LnRMSSD compared with the baseline monitoring period.

Unit of Measure: ln(ms)

Change in self-reported readiness to train from baseline monitoring to the final 3 days of supplementation. Readiness to train will be assessed using a single-item readiness-to-train rating scale scored from 1 to 10, where 1 indicates very poor readiness and 10 indicates excellent readiness. The outcome will be reported as the mean change in readiness-to-train score from the baseline monitoring period to the final 3-day supplementation period. Higher scores indicate greater perceived readiness to train.

Unit of Measure: points on a 1-10 scale

Change in self-reported fatigue from baseline monitoring to the final 3 days of supplementation. Fatigue will be assessed using the fatigue item of the Hooper and Mackinnon wellness questionnaire. The item is scored on a 1-7 scale. The outcome will be reported as the mean change in fatigue item score from the baseline monitoring period to the final 3-day supplementation period. Higher scores indicate greater perceived fatigue.

Unit of Measure: points on a 1-7 scale

Predictive performance of the predefined responder model in the independent validation cohort will be assessed using the area under the receiver operating characteristic curve. The model will compare predicted responder status with observed multidimensional responder status after 28 days of supplementation. Higher values indicate better discrimination.

Unit of Measure: area under the curve Post-completion clarification (November 2026): The originally planned AUROC analysis was not performed because a previously finalised prediction model was not available for independent validation. No prediction model was developed using the present cohort as a substitute. This deviation from the original analysis plan will be disclosed in the study publication.

Number of participants reporting at least one supplement-related adverse event during the 28-day supplementation period. Participants will be asked to report gastrointestinal symptoms, sleep disturbances, headache, palpitations, nervousness, or any other unusual symptoms.

Unit of Measure: participants

Change in response time during the football-specific video decision-making task from baseline to post-intervention testing after 28 days of supplementation. Response time will be measured as the time from presentation of the decision prompt to participant response. The outcome will be reported as the mean change in response time from baseline to post-intervention testing. Lower values indicate faster football-specific decision-making.

Unit of Measure: milliseconds

Change in football-specific decision-making accuracy from baseline to post-intervention testing after 28 days of supplementation. Decision-making accuracy will be assessed using a football-specific video decision-making task. Participants will view standardized football-specific scenarios and select the most appropriate tactical decision. The outcome will be reported as the mean change in the percentage of correct decisions from baseline to post-intervention testing. Higher values indicate better football-specific decision-making accuracy.

Unit of Measure: percentage of correct decisions

Change in visual search behavior from baseline to post-intervention testing after 28 days of supplementation. Visual search behavior will be assessed using eye-tracking during the football-specific video decision-making task. Time to first fixation will be defined as the time from scenario onset to the first fixation on the predefined optimal tactical option. The outcome will be reported as the mean change in time to first fixation from baseline to post-intervention testing. Lower values indicate faster visual orientation toward the optimal tactical option.

Unit of Measure: milliseconds