It is well established that oral caffeine administration (3-9 mg/kg) is ergogenic, enhancing numerous aspects of physical performance including strength and power. However, the extent to which these effects translate to volleyball-specific skills remains unclear. The purpose of this study was to systematically review the effects of acute caffeine ingestion on performance outcomes in volleyball-specific actions. A systematic review of published studies was conducted using scientific databases from their inception through December 2024 (registered in PROSPERO, CRD420251006314). We included studies with blinded crossover experimental designs that compared caffeine ingestion to a placebo in samples of volleyball players performing physical performance tests or volleyball-specific tasks. The data from these studies were meta-analyzed to calculate standardized mean differences (Hedges' g) between placebo and caffeine conditions, using a random-effects model. The Q and I2 statistic was calculated to verify the degree of similarity in the observed mean differences and the degree of heterogeneity, respectively. In total, after examining 60 effect sizes include 9 RCTs, 123 volleyball players with caffeine doses 1.7–6.4 mg/kg and administered 15–60 min pre-exercise, the meta-analysis indicated that caffeine improved performance in jumping activities (g = 0.24, p =0.009), strength-based tasks (g = 0.31, p =0.006) and performance in volleyball-specific skill tasks (g = 0.52, p =0.001). Specifically, subgroup analysis indicated significant improvement with caffeine in attack (g = 0.52, p =0.003), serve (g = 0.44, p =0.046) and accuracy (g = 0.68, p =0.001) tasks, but not in the velocity-based tasks (g = 0.26, p =0.168). Moreover, The I2 statistics showed low heterogeneity for the studies (I2 = 0 - 34.6). Acute caffeine ingestion appears to enhance physical performance in volleyball, with positive effects translating in jump and strength-based tests translated into improved skill execution during volleyball-specific tasks. Further research is needed to refine dosing strategies, account for individual differences based on habitual caffeine intake and player position, and assess long-term outcomes of caffeine intake.

Background/Objectives: Previous studies have linked chronic conditions and multimorbidity to lower physical activity, but evidence across individual movement behaviours remains limited. We examined associations between the number of self-reported chronic diseases and conditions and transport-related walking, leisure time physical activity, muscle-strengthening activity and sedentary behaviour among people aged ≥15 years in Serbia. Methods: Nationally representative 2019 Serbian National Health Survey data were analysed (n = 13,076 with complete information on 17 conditions). Complex sample logistic regression models were sequentially adjusted for sociodemographic characteristics, body mass index, functional mobility and self-rated health. Additional analyses assessed linear trends and departures from linearity using all covariates except self-rated health. Results: Overall, 51.4% reported no condition, 18.0% one and 30.6% two or more. All outcomes were associated with condition status before adjustment, but most associations were attenuated after including functional mobility. After full adjustment, an overall association remained only for muscle-strengthening activity on <2 days/week (Wald F = 5.13; p = 0.006). Compared with no condition, one condition was associated with higher odds (aOR 1.60, 95% CI 1.18–2.16), but two or more were not. Each additional condition was associated with 4.5% higher odds of sitting or reclining for ≥6 h/day (aOR 1.045, 95% CI 1.006–1.087; p = 0.025). No other linear trends were identified; muscle-strengthening activity showed a departure from linearity (p < 0.001). Conclusions: Associations differed across movement behaviour domains and were attenuated particularly after including functional mobility. The number of conditions alone only partially accounted for observed differences in movement behaviours.

Objectives: This secondary exploratory analysis of a randomized, double-blind, placebo-controlled crossover trial developed and compared indices linking administered caffeine dose to habitual intake to characterize variability in performance and side effects in wrestlers. Methods: Seventy-two male wrestlers completed a randomized, double-blind, placebo-controlled crossover trial in which they ingested caffeine (4 mg·kg⁻¹) or placebo 60 min before vertical jump and wrestling-specific testing. Three indices were calculated: DAR, expressing the administered dose as a multiple of the habitual intake; DDI, quantifying the additional caffeine received above habitual intake; and DNI, expressing this additional intake as a proportion of the administered dose. Hierarchical regression models were used to examine whether each index provided incremental explanatory value beyond habitual caffeine intake and absolute caffeine dose. Results: In exploratory hierarchical models adjusted for habitual caffeine intake and absolute dose, DAR was associated with additional explained variance for the change in total throws (ΔR² = 0.249, p < 0.001), the wrestling performance index (ΔR² = 0.321, p < 0.001), the Caffeine Utility Index (ΔR² = 0.160, p < 0.001), and side effect severity (ΔR² = 0.072, p = 0.008), but not for the change in vertical jump performance (ΔR² = 0.004, p = 0.586). DDI provided significant incremental explanatory value for the change in total throws (ΔR² = 0.061, p = 0.027) and the wrestling performance index (ΔR² = 0.067, p = 0.022). Exploratory quadratic analyses identified a theoretical DAR vertex range between 2.25 and 2.81. Conclusions: These findings support DAR as the principal index for prospective evaluation, but they do not establish a dosing prescription. DAR is not intended to replace body-mass-based dosing (mg·kg⁻¹); rather, it provides a complementary reference dimension that should be applied within established safety limits.