Browsing by Author "Erkan, Dilara"

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The Effect of Low Dose Caffeine Powder Supplementation on Serve Speed, Spike Speed, and Speed-Endurance in Elite Sitting Volleyball Players: A Randomized Double-Blind Crossover Study
(BMC, 2025) Diedhiou, Azize Bingol; Erkan, Dilara; Guler, Melek; Sar, Halit; Karakulak, Izzet; Eyuboglu, Ender; Yildirim, Ulas Can
BackgroundSitting volleyball relies heavily on upper-body strength and anaerobic capacity. Serve, spike, and speed-endurance are decisive skills, yet the ergogenic potential of low-dose caffeine in this Paralympic sport remains unclear.PurposeTo examine the acute effects of low-dose caffeine (3 mg/kg) supplementation on serve speed, spike speed, and speed-endurance in elite sitting volleyball players.MethodsUsing a randomized, double-blind, crossover design, 13 elite male athletes from the Turkish National Sitting Volleyball Team completed serve speed, spike speed, and speed-endurance tests under caffeine (CAF) and placebo (PLA) conditions.ResultsCaffeine intake produced a moderate improvement in serve speed (p = 0.028, d = 0.460); however, this effect did not remain statistically significant after Bonferroni correction (adjusted p = 0.084). No significant effects were observed for spike speed (p = 0.547, d = 0.166) or speed-endurance performance (p = 0.709, d = 0.111). Perceived exertion during the speed-endurance test was similarly high in both conditions.ConclusionsLow-dose caffeine may offer a trend toward improved serve performance, but the effect was not robust after statistical adjustment, and no benefits were observed for spike speed or speed-endurance. These findings highlight that caffeine's ergogenic effects are context-dependent and shaped by task complexity and sport-specific motor demands. Further research with larger and more diverse samples, genotype-based subgroups, and varied dosing strategies is warranted to clarify caffeine's role in adaptive sports.Trial registrationThe randomized controlled trial was retrospectively registered on 21/06/2025 at ClinicalTrials.gov, under the registration number NCT07056231.
Kültüre Özgü Mükemmeliyetçilik Örüntüleri: Çocuk Sporcular, Ebeveynleri ve Antrenörleri
(2025) Karakulak, İzzet; Tez, Özge Yavaş; Eyuboglu, Ender; Erkan, Dilara
Araştırmada, Türk kültürüne özgü spora ilişkin mükemmeliyetçilik örüntüleriyle ilişki olarak rekreasyonel amaçlı çeşitli sporlarla uğraşan çocuk sporcuların spora ilişkin mükemmeliyetçilik düzeylerinin demografik değişkenler açısından incelenmesi amaçlanmıştır. Kolayda örnekleme yöntemi gerçekleştirilen araştırmaya Türkiye’de çeşitli illerdeki spor kulüpleri altında yer alan rekreasyonel amaçlı çeşitli sporlarla (voleybol, futbol, yüzme, tenis, cimnastik ve basketbol) ilgilenen 394 çocuk sporcudan veriler toplanmıştır. Veri toplama aracı olarak “Sporda Mükemmel Performans Ölçeği (Çocuk Formu)” kullanılmıştır. Verilerin analizinde tanımlayıcı istatistikler, T-testi, Anova, Post-Hoc analizleri kullanılmıştır. T-testi analizi sonuçları, cinsiyet ve yaş değişkenleri ile cinsiyet, ebeveyn baskısı ve antrenör baskısı değişkenlerinin performans mükemmeliyetçiliği ile anlamlı bir ilişkisi olduğunu göstermiştir (p
Varying Doses of Evening Caffeine Ingestion Have Different Effects on Rowing Ergometer Performance, Sleep Quality, and Wakefulness Scores
(Frontiers Media SA, 2025) Karakulak, Izzet; Yildirim, Ulas Can; Erkan, Dilara; Karayigit, Raci; Eyuboglu, Ender; Diedhiou, Azize Bingol; Akca, Firat
Introduction: This study investigated the dose-dependent effects of evening caffeine ingestion on rowing performance, sleep quality, and daytime sleepiness in trained male rowers. Methods: 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 2,000 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 2,000 m rowing ergometer (Concept II, United States) 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: 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. Discussion: These findings indicate a clear dose-response relationship, wherein higher evening caffeine intake improves performance but has 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.