Varying Doses of Evening Caffeine Ingestion Have Different Effects on Rowing Ergometer Performance, Sleep Quality and Wakefulness Scores

Izzet Karakulak¹Ulas Can YILDIRIM^2,3*Dilara ERKAN⁴Raci Karayigit⁵ENDER EYUBOGLU⁶Azize Bingol Diedhiou⁷Mehmet Can Gundem⁸Selin Yildirim Tuncer⁹Halit Sar¹⁰Gökmen Ozen¹¹Firat Akca^5*

• ¹Department of Sport Management, Faculty of Sport Sciences, Mardin Artuklu University, Mardin, Türkiye
• ²Sinop University, Sinop, Türkiye
• ³Department of Coaching Education, Faculty of Sport Sciences, Sinop University, Sinop, Türkiye
• ⁴Department of Physical Education and Sports, Institute of Health Sciences, Faculty of Sport Sciences, Ankara University, Ankara, Türkiye
• ⁵Department of Coaching Education, Faculty of Sport Sciences, Faculty of Sport Sciences, Ankara University, Ankara, Türkiye
• ⁶Department of Coaching Education, Faculty of Sport Sciences, Bartın University, Bartin, Türkiye
• ⁷Department of Coaching Education, Scholl of Physical Education and Sports, Şırnak University, Sirnak, Türkiye
• ⁸Department of Sport Management, Faculty of Sport Sciences, Sinop University, Sinop, Türkiye
• ⁹Department of Coaching Education, Faculty of Sport Sciences, Lokman Hekim University, Ankara, Türkiye
• ¹⁰Department of Coaching Education, Faculty of Sport Sciences, Lokman Hekim University, Sinop, Türkiye
• ¹¹Department of Physical Education and Sports Education, Faculty of Sport Sciences, Çanakkale Onsekiz Mart University, Çanakkale, Türkiye

This study investigated the dose-dependent effects of evening caffeine ingestion on rowing performance, sleep quality, and daytime sleepiness in trained male rowers. Using a double-blind, randomized, crossover design, 13 university-level rowers (mean age = 22.07 ± 2.21 years; mean body mass = 77.66 ± 6.45 kg) completed four 2000 m time-trial sessions between 19:00 and 20:00 h under placebo (PLA), low-dose capsule caffeine (3 mg/kg, LDC), moderate-dose capsule caffeine (6 mg/kg, MDC), and high-dose capsule caffeine (9 mg/kg, HDC) conditions. Performance metrics, heart rate, and subjective sleep assessments were collected. Rowing performance was assessed by a standard 2000 m rowing ergometer (Concept II, USA) time trial. Sleep quality was measured with a numerical rating scale in the morning after each trial, and daytime sleepiness was measured with the Karolinska Sleepiness Scale. Results indicated significantly improved rowing times and power output with HDC and MDC compared to PLA (p < 0.05), with HDC yielding the most notable enhancements (d = 0.40– 0.41). However, these ergogenic benefits were accompanied by significantly impaired sleep quality and elevated daytime sleepiness in both HDC and MDC groups (p < 0.01, d = 1.3–1.5). Notably, adverse effects such as headache, insomnia, and gastrointestinal discomfort were predominantly reported in the HDC condition (p < 0.05). Although LDC offered mild performance improvements with minimal sleep disruption, only the high dose condition exhibited large physiological and perceptual trade-offs. These findings indicate a clear dose–response relationship, wherein higher evening caffeine intake improves performance but have detrimental effects on sleep and recovery markers. Coaches and athletes should carefully balance caffeine dosing against potential recovery costs, especially in evening training or competition contexts.