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.

Background and Objectives: This study investigated the efficacy of eccentric isokinetic muscle strengthening versus passive motion protocols on neuromuscular function and performance capacity in female swimmers with chronic lateral epicondylitis. Materials and Methods: Twenty-five swimmers (age 46.1 ± 3.1 years) with lateral epicondylitis exceeding three months’ duration completed a randomized controlled trial comparing eccentric training in Controlled Active Motion mode (experimental group (EG), n = 13) against passive motion in Continuous Passive Motion mode (control group (CG), n = 12). Both groups performed 18 supervised sessions over six weeks (60°/s angular velocity, progressive loading 1–12 sets × 5 repetitions). Bilateral concentric peak torque of elbow extensors and flexors constituted the primary outcomes. Secondary measures included push-up performance, explosive power assessed by the Seated Medicine Ball Chest Push Test, and goniometric range of motion. Linear mixed-effects models and analysis of covariance with baseline adjustment were employed. Results: Eccentric training produced side-specific strength adaptations in elbow flexors (confirmed interaction: F_1,23 = 8.56, p = 0.008, η_p² = 0.271), with the experimental group demonstrating balanced bilateral gains, whereas the control group exhibited asymmetric responses favoring the non-dominant limb. EG demonstrated superior functional gains: push-up repetitions increased 4.15 ± 1.77 versus 2.17 ± 1.27 in CG (adjusted difference = 3.21 repetitions, 95% CI [1.52, 4.90], p = 0.001, d = 1.31), while explosive power improved 0.32 ± 0.09 m versus 0.10 ± 0.06 m (adjusted difference = 0.35 m, 95% CI [0.25, 0.45], p < 0.001, d = 1.20). Range of motion remained unchanged across groups (all p > 0.65). Conclusions: Eccentric isokinetic strengthening confers substantial advantages over passive motion protocols for restoring upper-body muscular endurance and ballistic force production in swimmers with lateral epicondylitis, supporting its integration into rehabilitation frameworks for the management of tendinopathy.

Background and Objectives: This study investigated whether crossover neuromuscular fatigue following unilateral handgrip exercise exhibits directional asymmetry, testing whether dominant-limb fatigue produces greater contralateral performance decrements than non-dominant-limb fatigue in adults and pre-peak-height-velocity children. Materials and Methods: Thirty-three healthy, right-handed males (16 adults: 22.5 ± 1.6 years; 17 pre-peak-height-velocity boys: 11.2 ± 0.8 years, maturity offset −2.2 ± 0.4 years) completed three counterbalanced experimental sessions (48–72 h apart): dominant-arm fatigue, non-dominant-arm fatigue, and control. The fatigue protocol consisted of 20 consecutive 6 s maximal voluntary isometric handgrip contractions. Primary outcomes were percentage changes in maximal voluntary isometric contraction of the contralateral limb across handgrip, elbow flexor, and elbow extensor muscle groups. Results: The experimental condition explained approximately 64% of crossover variance in adults (η_p² = 0.650, ηG² = 0.421) and children (η_p² = 0.638, ηG² = 0.448; both p < 0.001). Dominant-limb fatigue elicited substantially greater contralateral decrements than non-dominant-limb fatigue in adults (−11.00% vs. −3.92%, dz = −1.07) and children (−12.71% vs. −3.08%, dz = −1.33), representing 2.5- to 3.5-fold greater transfer efficiency (both p < 0.001). Age-group comparisons revealed no differences in crossover susceptibility (p = 0.627, η_p² = 0.008), with equivalence testing confirming developmental invariance. Crossover effects extended to heterologous proximal muscles without magnitude differences (p > 0.13). Conclusions: Crossover fatigue (contralateral performance decrement following unilateral exercise) exhibited directional asymmetry, with dominant-limb protocols eliciting 2.5- to 3.5-fold greater contralateral decrements. This pattern aligns with asymmetric transcallosal inhibitory projections demonstrated in prior transcranial magnetic stimulation studies, though direct neurophysiological confirmation was not obtained. Functional equivalence between pre-peak-height-velocity children and adults indicates that interhemispheric transfer mechanisms achieve operational maturity before peak height velocity. Extension to heterologous muscles implicates supraspinal mechanisms. The findings establish normative parameters for clinical populations with compromised transcallosal integrity.

This investigation examined whether mirror visual feedback modulates crossover fatigue magnitude during unilateral handgrip exertion and whether efficacy demonstrates age-dependent and muscle-group-specific characteristics. Thirty-three participants stratified by developmental stage (adults: n = 17, 24.64 ± 5.38 years; children: n = 16, 11.87 ± 0.79 years) completed a randomized controlled crossover protocol incorporating three visual feedback conditions: mirror reflection of the exercised limb, occluded vision (no-mirror), and passive rest control. Participants performed unilateral dominant handgrip fatigue induction (20 × 6 s maximal voluntary isometric contractions) while bilateral force production was quantified pre-intervention and post-intervention across handgrip, elbow flexion, and elbow extension domains. Linear mixed-effects models with participant-specific random intercepts and slopes quantified Condition × Time × Limb interactions. In the non-exercised contralateral limb, linear mixed-effects models demonstrated that under the mirror condition, non-dominant handgrip force was maintained at rest-equivalent levels relative to control (+0.02 kg, 95% CI [−1.15, +1.17], p = 0.987, dz =+ 0.003), whereas vision occlusion induced significant crossover fatigue (−3.37 kg [−4.40, −2.35], p < 0.001, dz =− 1.16). All contrasts represent within-subject difference-of-differences in non-dominant limb change score (Post − Pre) extracted from the full factorial LMM via emmeans within the Limb = Non-dominant stratum pooled across age groups. The mirror versus no-mirror comparison yielded +3.38 kg [+2.43, +4.34], p < 0.001, dz =+ 1.26. Age-stratified analyses confirmed comparable effect magnitudes (adults: dz =+ 1.40; children: dz =+ 1.33). Muscle-group specificity emerged for handgrip but not elbow flexion (p = 0.068) or extension (p = 0.156). Age Group × Condition × Time × Limb interactions were non-significant (all p > 0.16), providing no evidence of age moderation within the tested developmental range. Mirror visual feedback constitutes an effective countermeasure against crossover fatigue in distal upper limb musculature. The magnitude of mirror-induced attenuation did not differ between children (aged 10–13 years) and adults within our sample, with no statistically detectable age moderation within the tested developmental range; formal equivalence testing was not conducted. Effects demonstrated anatomical selectivity, favoring hand musculature over proximal elbow musculature.

Aim: Female athletic performance is shaped by the convergence of menstrual-cycle timing, circadian rhythms, fatigue, and ergogenic supplementation; yet no prior study has examined these factors simultaneously in a sport-specific setting. This study investigated the independent and combined effects of acute caffeine ingestion, calendar-based testing window, time of day, and match-induced fatigue on psychophysiological, cognitive, and physical performance in trained female volleyball players. Methods: Thirteen elite eumenorrheic female volleyball players (age: 24.23 ± 4.06 years) completed a randomized, double-blind, placebo-controlled crossover protocol comprising 12 sessions corresponding to all combinations of testing window (menstrual, follicular, luteal), supplementation (caffeine 6 mg·kg⁻¹ vs. placebo), and time of day (08:00 h vs. 18:00 h). Assessments included the Epworth Sleepiness Scale, Pittsburgh Sleep Quality Index, Spiegel questionnaire, Profile of Mood States, Hooper Index, Stroop task, Countermovement Jump (CMJ), Modified Agility T-Test (MAT), and Reactive Agility Test (RAT), administered before and after a one-hour simulated match. Results: Significant main effects of testing window, caffeine, time of day, and fatigue state were observed across all outcome domains (all p < 0.05). Caffeine reduced daytime sleepiness (F(1,12) = 23.84, p < 0.001, ηp² = 0.665), enhanced vigor (F(1,12) = 114.10, p < 0.001, ηp² = 0.905), and improved MAT performance (F(1,12) = 33.27, p < 0.001, ηp² = 0.735). The follicular window was associated with superior cognitive, neuromuscular, and mood-related outcomes relative to the menstrual and luteal windows. Exploratory higher-order interactions suggested condition-specific caffeine benefits for MAT, RAT, and CMJ, particularly in afternoon post-fatigue conditions; these patterns require replication in larger samples. Conclusions: Acute caffeine ingestion improved several psychophysiological, cognitive, and neuromuscular outcomes in trained female volleyball players, with effects that varied across calendar-based testing windows, time of day, and fatigue state. Individualized supplementation strategies incorporating cycle timing and circadian context remain investigational; prescriptive recommendations require replication in larger, hormonally verified samples before clinical or applied adoption.