Caffeine Dose: Performance and Recovery

Ulaç Can YILDIRIM13 enrolled

Overview

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.

Study Type

INTERVENTIONAL

Allocation

RANDOMIZED

Purpose

Interventions

Cellulose PowderDIETARY_SUPPLEMENT

Participants consumed an inert cellulose powder dissolved in water, containing no active caffeine. The placebo was ingested orally 60 minutes prior to the rowing performance test. This condition served as the control and was administered once per session in a randomized, double-blind, crossover design.

Caffeine 3 mg/kg Oral PowderDIETARY_SUPPLEMENT

Participants consumed caffeine in powder form at a dose of 3 milligrams per kilogram of body weight. The powder was dissolved in water and ingested orally approximately 60 minutes before the start of the 2000-meter rowing ergometer performance test. The intervention was administered once per session in a randomized, double-blind, crossover design.

Caffeine 6 mg/kg Oral PowderDIETARY_SUPPLEMENT

Participants ingested caffeine in powder form, dissolved in water, at a dose of 6 milligrams per kilogram of body mass. The solution was consumed orally 60 minutes prior to the 2000-meter rowing performance test. This intervention was administered once per session as part of a randomized, double-blind, crossover design.

Caffeine 9 mg/kg Oral PowderDIETARY_SUPPLEMENT

A powdered caffeine dose of 9 milligrams per kilogram was dissolved in water and consumed orally by participants 60 minutes before a 2000-meter rowing ergometer trial. The intervention was administered once per session under a randomized, double-blind, crossover design.

Eligibility

Sex: MALEMin age: 20 YearsMax age: 25 YearsHealthy volunteers:

Medical Language ↔ Plain English

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

Outcomes

Primary Outcomes

Change in 2000-meter Rowing Ergometer Completion Time (seconds) Following Varying Doses of Evening Caffeine Ingestion

The time in seconds required to complete a 2000-meter rowing ergometer trial was recorded under four separate conditions: placebo, and caffeine doses of 3 mg/kg, 6 mg/kg, and 9 mg/kg. Each participant completed one trial per condition in a randomized, double-blind, crossover design. Performance was measured using a Concept2 rowing ergometer with integrated time-tracking software. Trials were conducted in the evening (between 6:00 PM and 9:00 PM), approximately 60 minutes after ingestion of the assigned supplement. A lower time indicates better performance.

Time frame: Approximately 60 minutes post-ingestion on each test day, during evening sessions (between 6:00 PM and 9:00 PM)

Subjective Sleep Quality Score (5-point Likert Scale)

Participants rated their perceived sleep quality the morning after each trial using a 5-point Likert scale (1 = very poor, 5 = very good). Scores reflect subjective assessment of sleep quality following evening caffeine ingestion.

Time frame: Morning following each test day (approximately 10-12 hours post-dose)

Mean Power Output (Watts) During 2000-meter Rowing Ergometer Trial

Average power output (in watts) generated by participants during each 2000-meter rowing trial. Power was recorded via Concept2 ergometer's internal performance monitor, calculated over the full distance. A higher value indicates better performance.

Time frame: Approximately 60 minutes post-ingestion on each test day, during evening sessions (between 6:00 PM and 9:00 PM)

Daytime Sleepiness Score (Epworth Sleepiness Scale)

Daytime sleepiness was assessed using the Epworth Sleepiness Scale (ESS), a validated questionnaire consisting of 8 items, each scored from 0 to 3. Total scores range from 0 (no sleepiness) to 24 (severe sleepiness). Higher scores indicate more sleepiness.