Caffeine mouth rinsing in small-sided volleyball games: Differential effects of continuous versus intermittent formats on psychophysiological, mood, and technical responses in young female players

This study aimed to investigate the effects of caffeine mouth rinsing (CAF-MR) on psychophysiological responses, mood, and technical performance during 4-a-side small-sided games (SSGs) performed under different formats in amateur female volleyball players. Twenty-four players (age: 17.33 ± 2.43 years) completed four randomized conditions in a repeated-measures counterbalanced design: caffeine-intermittent (CAF-INT), caffeine-continuous (CAF-CONT), placebo-intermittent (PLA-INT), and placebo-continuous (PLA-CONT). Participants rinsed a caffeine solution (200 mg) or placebo for 10 s prior to exercise. Technical performance (successful and unsuccessful passes) was assessed via video analysis, whereas psychophysiological responses included heart rate (HR), rating of perceived exertion (RPE), enjoyment, mental effort, and mood states. A one-way repeated-measures analysis of variance revealed significant differences between conditions for successful passes (p = 0.001, ηp² = 0.397), with higher values observed in CAF-CONT compared to other conditions. Unsuccessful passes were significantly greater in CAF-INT (p = 0.001, ηp² = 0.751). HRmax differed significantly between conditions (p = 0.002), with higher values in PLA-CONT compared to CAF-INT and PLA-INT. No significant differences were found for HRmean, RPE, enjoyment, or mental effort (p > 0.05). Regarding mood responses, For the anger subscale, the condition × time interaction was not significant (F(3,92) = 2.601, p = 0.057, η_p^2 = 0.078). Similarly, no significant interaction effects emerged for the confusion subscale (F(3,92) = 1.642, p = 0.185, η_p^2= 0.051), the fatigue subscale (F(3,92) = 0.196, p = 0.899, η_p^2 = 0.006), the depression subscale (F(3,92) = 0.548, p = 0.651, η_p^2= 0.018), the tension subscale (F(3,92) = 0.424, p = 0.736, η_p^2= 0.014), or the vigor subscale (F(3,92) = 0.986, p = 0.403, η_p^2= 0.031). In conclusion, CAF-MR appears to enhance technical performance in continuous SSG formats but may impair performance in intermittent formats. These findings suggest that the ergogenic effects of CAF-MR are context-dependent and influenced by game structure.