Browsing by Author "Eyuboglu, Ender"

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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.
Exercise, Addiction and Motivation: the Development of a Motivation Scale in Extreme Sports as a Sport of Challenge with Nature
(Frontiers Media S.A., 2025) Karakulak, Izzet; Yavas, Ozge; Bora, Mehmet Veysi; Eyuboglu, Ender; Aslan, Cem Sinan; Aydemir, Ahmet; Sahin, Fatma Nese
In the extant literature, the concepts of motivation and addiction have been employed to elucidate how a considerable number of unpleasant experiences for extreme sports participants can eventually become rewarding. The objective of this study was to develop a scale to measure the behavioral addiction levels of extreme sports athletes. A plethora of addiction and motivation scales (MS) exists; however, none of them are measurement tools that can assess emotional responses and simultaneously address motivation and addiction. Moreover, they are not specific to extreme sports participants. The present study comprised 1,073 participants engaged in extreme sports and incorporated psychometric analyses encompassing a literature review, expert review, exploratory and confirmatory factor analysis. The MS factor structure was determined using the Principal Axis Factoring (PAF) method. The analysis yielded a three-factor structure comprising 16 items, accounting for 63.00% of the total variance. In order to validate the structure, first- and second-order factor analysis was performed. The fit indices obtained at both levels were consistent with the acceptable limits specified in the literature. In the final results, 16 items related to three factors, namely "hedonic deprivation," "tolerance," and "hedonic opposition," were validated. Furthermore, the AVE, CR, and root AVE values were calculated. The analysis results indicated that each sub-dimension in the measurement model exhibited a distinct structure and fulfilled the established validity criteria. Cronbach's Alpha and Split-Half coefficients were calculated to ascertain the reliability of the measurement. The floor and ceiling effects of the MS were also examined. Finally, ROC analysis was employed to evaluate the measurement tool. The findings of this research indicate that the MS, which has been developed and comprises 16 items and a three-factor structure, is a valid and reliable instrument capable of simultaneously addressing motivation and addiction in the context of extreme sports. The scale is of significance as it is the inaugural quantitative measurement tool with the capacity to assess addiction. In conclusion, the MS provides a novel, theory-based contribution to the literature by integrating motivation and behavioral addiction within a single, psychometrically validated framework specific to extreme sports.
Citation - WoS: 12
Citation - Scopus: 11
Impact of Detraining Process Experienced During the Covid-19 Pandemic on the Selected Physical and Motor Features of Football Players
(Mattioli 1885, 2020) Korkmaz, Sezgin; Aslan, Cem Sinan; Eyuboglu, Ender; Celebi, Murat; Kir, Ridvan; Karakulak, Izzet; Geri, Serdar
Study Objectives: The purpose of this study was to examine the changes in the selected physical and physiological properties of football players in the long-term detraining stage during the pandemic period. Methods: In this study, 14 semi-professional football players (mean age: 22.21 +/- 3.29 years old and mean height: 177.86 +/- 5.35 cm) took part voluntarily. The participants had remained in detraining in the home environment for 89 days until the final measurements, following the decision of cessation of the leagues made by the Turkish Football Federation, except soft and irregular exercises they did with theirbody weight. The participants' body composition characteristics, anaerobic performance, flexibility, and speed performance were measured. The descriptive statistics for numeric variables were expressed as mean standard deviation. Since parametric test assumptions were provided as a result of examining the data acquired from the experimental subjects via the Shapiro-Wilk test, the repetitive measurements were evaluated using the "Paired-Sample t-test". In addition, the mathematical differences between the two measurements were indicated with percentage. The results were evaluated at the confidence interval of 95% and the value p <0.05 was accepted to be significant. Results: Comparing the pretest-posttest results of the participants; the difference between the two measurements was statistically insignificant in terms of body weight, BMI, 30 m speed, and fatigue index properties, while the difference in terms of body muscle mass, fat mass, fat ratio, waist-hip ratio, peak power, average power, minimum power and flexibility properties was significant. Conclusion: A long-term detraining process significantly damages the physical and motor performance of football players.
Citation - WoS: 7
Citation - Scopus: 10
Is There Any Effect of Non-Suitable Pull Technique in Back & Leg Dynamometers on the Leg Strength Test Results
(Carbone Editore, 2019) Aslan, Cem Sinan; Karakulak, Izzet; Sahin, Fatma Nese; Eyuboglu, Ender
Introduction: Dynamometers are valid and reliable test instruments that have been used for many years to measure strength. However, there are excessive differences in leg strength scores in different studies with similar groups. This situation suggests a non-conformity to testing procedures occurred during the practice of the tests. The purpose of this study was to determine the effect of non-suitable pulling technique on the leg strength test results. Materials and methods: A total of 127 healthy subjects (24 female athletes and 41 male athletes, 22 sedentary females and 40 sedentary males) were included in the study. A back & leg Dynamometer was used to determine the leg strength of the participants. The participants pulled up the dynamometer's grab handle with and without contact with their upper leg. Results: The results showed that there was a significant difference (p=0.000) between contacted and non-contact pulling trials of all participants. The percentage difference of leg strength between contacted and non-contact pull was 51.69% (43.25 kg) for female athletes, 54.78 (73.46 kg) for male athletes, 5631% (37.52 kg) for sedentary females, and 50.69% (65.55 kg) for sedentary males. Conclusion: There were significant differences between contacted and non-contact pull trials. It was determined that during the pulling phase if the dynamometer's grab-handle contacted the upper leg of a subject, the strength measurement's score increased considerably. In this case, it can be said that non-suitable pulling technique in the "back & leg dynamometers" affects the leg strength test scores.
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.