Altered Glymphatic-Related MRI Metrics and Brain Network Reorganization in Drug-Naive Children With Self-Limited Epilepsy With Centrotemporal Spikes.

Repeated sprint ability (RSA) is a fundamental determinant of performance in many intermittent sports, including football, rugby, hockey and basketball. Where decisive moments frequently require athletes to perform repeated maximal efforts interspersed with brief and incomplete recovery periods [,]. The ability to maintain sprint performance across successive bouts is therefore critical to successful match play and is influenced by the integrated contribution of neuromuscular function, metabolic capacity and central nervous system regulation [,]. Importantly, RSA exhibits a pronounced time-of-day dependence, with performance consistently lower during the morning than the late afternoon or evening [,]. Despite this, athletes are frequently required to train and compete during morning hours because of tournament scheduling, travel demands and environmental constraints [,]. Consequently, identifying practical strategies capable of attenuating these morning decrements in repeated sprint performance has become an important objective for athletes, coaches and practitioners, yet evidence supporting effective interventions remains limited [,]. The physiological basis of diurnal variation in repeated sprint performance is thought to reflect the circadian regulation of multiple interacting systems that collectively influence exercise capacity. Peak physical performance typically occurs during the late afternoon or early evening [], coinciding with the acrophase (peak) of core body temperature [,]; whereas, performance is generally attenuated during the morning biological phase. These time-of-day differences are accompanied by alterations in neuromuscular activation, muscle contractile properties, muscle temperature, metabolic responses and central nervous system function, which collectively influence force production, power output and fatigue resistance during repeated high-intensity exercise [,,,]. Although the precise contribution of each mechanism remains uncertain, converging evidence suggests that the interaction between central and peripheral physiological processes underpins the reduced repeated sprint performance observed during the morning [,]. Consequently, interventions capable of attenuating these circadian-related physiological limitations may provide meaningful benefits for athletic performance during morning training and competition. Among the nutritional strategies proposed to mitigate morning reductions in exercise performance, acute caffeine ingestion is one of the most widely used and extensively investigated ergogenic aids [,]. Caffeine (1,3,7-trimethylxanthine) primarily exerts its ergogenic effects through antagonistic activity on adenosine receptors within the central nervous system, increasing arousal and neurotransmitter activity and reducing perception of fatigue. Leading to increased arousal, reducing perceptions of fatigue and enhancing neurotransmitter activity including dopamine and noradrenaline, which collectively promote wakefulness, attention and motor drive [,,]. These mechanisms provide a strong physiological rationale for caffeine as a potential countermeasure to the circadian-related reductions in physical performance observed during the morning. Indeed, caffeine has consistently been shown to improve neuromuscular [], time-trial performance [] and exert a small beneficial effect on muscular endurance performance []. However, evidence relating to repeated sprint performance appears to depend on the caffeine naivety of the population, measure (set distance or set time), exercise mode and the administered caffeine dose; a more pronounced enhancement was observed with doses ≥ 6 mg·kg body weight within cycling-based repeated sprint performance compared with running-based protocols [,,,,,,]. Consequently, caffeine seems to represent a biologically plausible intervention capable of offsetting the physiological constraints associated with morning exercise performance.