The goal of this clinical trial is to learn how different doses of caffeine taken in the evening affect rowing performance, sleep quality, and daytime alertness in trained male university rowers. The main questions it aims to answer are:

Does a low, moderate, or high caffeine dose improve rowing performance? How do these doses affect sleep and recovery after evening exercise? Participants completed four rowing tests after consuming either a placebo, low (3 mg/kg), moderate (6 mg/kg), or high (9 mg/kg) dose of caffeine. Researchers measured rowing time, power, heart rate, sleep quality, and daytime sleepiness.

The study found that moderate and high caffeine doses improved rowing performance the most. However, these same doses made it harder for participants to sleep well and feel alert the next day. Headaches and stomach issues were also more common with the high dose. The low dose gave smaller performance gains but caused fewer side effects.

This study shows that evening caffeine can boost performance but may hurt recovery and sleep. Athletes and coaches should weigh these trade-offs when using caffeine for late-day training or competition.

This double-blind, randomized crossover study examined the dose-dependent effects of evening caffeine ingestion on rowing performance, sleep quality, and daytime alertness in trained male university rowers. The rationale stems from increasing use of caffeine as a performance-enhancing supplement in evening training or competition settings, despite its known adverse effects on sleep and recovery. Thirteen participants completed four experimental trials (placebo, 3 mg/kg, 6 mg/kg, 9 mg/kg caffeine), each separated by a washout period, during which they performed a 2000-meter rowing time trial and were assessed for sleep quality and daytime sleepiness using validated scales. The study also recorded physiological responses and adverse events across conditions. By evaluating multiple doses, the design allowed for assessment of both efficacy and tolerability thresholds, supporting dose-optimization strategies. This study aims to inform practical guidelines for athletes and coaches balancing acute ergogenic benefits with potential recovery trade-offs when caffeine is used late in the day.

Inclusion Criteria:

• Male university-level rowers
• Aged approximately 22 ± 2.2 years
• Minimum of 2 years of rowing training experience
• Free of any medical condition that impairs exercise participation
• Regular caffeine consumers (habitual daily intake recorded)
• Voluntarily signed informed consent form
• Available to attend all scheduled laboratory sessions

Exclusion Criteria:

• Any medical condition that could interfere with study participation or protocol adherence
• Use of prescription medications during the study period
• Known allergy to mannitol or other artificial sweeteners
• Diagnosed sleep disorders (e.g., insomnia, sleep apnea)
• Physician's advice to limit or avoid caffeine intake

Individual participant data (IPD) underlying the results reported in the publication, including performance outcomes, sleep-related metrics, and adverse event reports, will be made available upon reasonable request to qualified researchers. Data will be de-identified to protect participant confidentiality. The data will become accessible after publication of the main results and will be available for up to five years. A data dictionary will also be provided to facilitate proper interpretation.

Individual participant data (IPD) will be available beginning 6 months after publication of the study results and will be accessible for up to 5 years.

Qualified researchers who provide a methodologically sound proposal will be granted access to the deidentified individual participant data. Proposals should be submitted to [your email address or institutional contact]. Access will be granted for research purposes only and in accordance with data use agreements.