Differential Time-of-Day Effects of Caffeine Capsule and Mouth Rinse on Cognitive Performance in Adolescent Male Volleyball Athletes: A Randomized Crossover Investigation

Amor, Salma Belhaj; Dhahbi, Wissem; Bougrine, Houda; Bessifi, Manel; Geantă, Vlad Adrian; Ursu, Vasile Emil; Trabelsi, Khaled; Souissi, Nizar

doi:10.3390/life16010033

Open AccessArticle

Differential Time-of-Day Effects of Caffeine Capsule and Mouth Rinse on Cognitive Performance in Adolescent Male Volleyball Athletes: A Randomized Crossover Investigation

by

Salma Belhaj Amor

^1,2,

Wissem Dhahbi

^3,4

,

Houda Bougrine

^1,5

,

Manel Bessifi

³,

Vlad Adrian Geantă

^6,7,*

,

Vasile Emil Ursu

^8,*

,

Khaled Trabelsi

^9,10

and

Nizar Souissi

^1,11

¹

Physical Activity, Sport and Health Research Unit (UR18JS01), National Observatory of Sports, Tunis 1003, Tunisia

²

High Institute of Sports and Physical Education of El Kef, University of Jendouba, El Kef 7100, Tunisia

³

Research Unit (UR22JS01) “Sport Sciences, Health and Movement”, High Institute of Sport and Physical Education of Kef, University of Jendouba, El Kef 7100, Tunisia

⁴

Training Department, Police College, Qatar Police Academy, Doha 7157, Qatar

⁵

High Institute of Sport and Physical Education of Gafsa, Gafsa University, Gafsa 2112, Tunisia

⁶

Department of Physical Education and Sport, Faculty of Physical Education and Sport, Aurel Vlaicu University of Arad, 310025 Arad, Romania

⁷

Doctoral School of Sport Science and Physical Education, Pitești University Center, National University of Science and Technology Politehnica Bucharest, 110253 Pitești, Romania

⁸

Department of Physical Education and Sport, Faculty of Law and Social Sciences, University “1 Decembrie 1918” of Alba Iulia, 510009 Alba Iulia, Romania

⁹

Research Laboratory Education, Motricité, Sport et Santé, EM2S, LR19JS01, High Institute of Sport and Physical Education of Sfax, University of Sfax, Sfax 3000, Tunisia

¹⁰

Department of Movement Sciences and Sports Training, School of Sport Science, The University of Jordan, Amman 28002, Jordan

¹¹

High Institute of Sport and Physical Education, University of Manouba, Ksar-Said, Mannouba 2010, Tunisia

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^*

Authors to whom correspondence should be addressed.

Life 2026, 16(1), 33; https://doi.org/10.3390/life16010033

Submission received: 28 November 2025 / Revised: 15 December 2025 / Accepted: 22 December 2025 / Published: 25 December 2025

(This article belongs to the Section Physiology and Pathology)

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Abstract

Caffeine is widely used to enhance cognitive performance, but its efficacy may vary with the administration route and circadian timing. This study compared the acute effects of caffeine capsule ingestion and caffeine mouth rinsing on cognitive performance across morning, midday, and evening sessions in well-trained, adolescent male volleyball players. Twenty-four athletes completed three randomized, double-blind, crossover trials involving a caffeine capsule (3 mg·kg⁻¹), a caffeine mouth rinse of the same dose (expectorated), and a placebo. Cognitive performance was assessed using simple and choice reaction time tests and the Stroop task, alongside a side-effects questionnaire. Both caffeine forms improved performance versus the placebo, with the greatest enhancements occurring at midday and moderate benefits evident in the morning. Capsule ingestion produced the most consistent improvements across reaction speed and executive control, whereas mouth rinsing elicited smaller, task-dependent effects, particularly at midday. No consistent or practically relevant benefits were observed for either caffeine condition in the evening, when cognitive performance was naturally highest. Side effects were mild and infrequent, with occasional headaches after capsule ingestion. These findings indicate that caffeine capsules most effectively enhance cognitive performance when baseline alertness is suboptimal, while caffeine mouth rinsing represents a practical ingestion-free alternative with moderate efficacy.

Keywords: methylxanthines; orosensory stimulation; psychomotor speed; ergogenic aids; diurnal variation; youth sports

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MDPI and ACS Style

Amor, S.B.; Dhahbi, W.; Bougrine, H.; Bessifi, M.; Geantă, V.A.; Ursu, V.E.; Trabelsi, K.; Souissi, N. Differential Time-of-Day Effects of Caffeine Capsule and Mouth Rinse on Cognitive Performance in Adolescent Male Volleyball Athletes: A Randomized Crossover Investigation. Life 2026, 16, 33. https://doi.org/10.3390/life16010033

AMA Style

Amor SB, Dhahbi W, Bougrine H, Bessifi M, Geantă VA, Ursu VE, Trabelsi K, Souissi N. Differential Time-of-Day Effects of Caffeine Capsule and Mouth Rinse on Cognitive Performance in Adolescent Male Volleyball Athletes: A Randomized Crossover Investigation. Life. 2026; 16(1):33. https://doi.org/10.3390/life16010033

Chicago/Turabian Style

Amor, Salma Belhaj, Wissem Dhahbi, Houda Bougrine, Manel Bessifi, Vlad Adrian Geantă, Vasile Emil Ursu, Khaled Trabelsi, and Nizar Souissi. 2026. "Differential Time-of-Day Effects of Caffeine Capsule and Mouth Rinse on Cognitive Performance in Adolescent Male Volleyball Athletes: A Randomized Crossover Investigation" Life 16, no. 1: 33. https://doi.org/10.3390/life16010033

APA Style

Amor, S. B., Dhahbi, W., Bougrine, H., Bessifi, M., Geantă, V. A., Ursu, V. E., Trabelsi, K., & Souissi, N. (2026). Differential Time-of-Day Effects of Caffeine Capsule and Mouth Rinse on Cognitive Performance in Adolescent Male Volleyball Athletes: A Randomized Crossover Investigation. Life, 16(1), 33. https://doi.org/10.3390/life16010033

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Differential Time-of-Day Effects of Caffeine Capsule and Mouth Rinse on Cognitive Performance in Adolescent Male Volleyball Athletes: A Randomized Crossover Investigation

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