Endurance athletes, glycogen

Physically active men and women commonly report carbohydrate intakes similar to weight-matched inactive adults (45 to 55% of daily energy intake, or 5 g/kg body weight/day). In general, these intakes may be adequate to meet the carbohydrate needs of recreational or fitness athletes who participate in moderate levels of activity up to 1 h daily. In contrast, endurance athletes who train with more intense activities that deplete muscle glycogen may have greater carbohydrate needs to ensure adequate muscle glycogen concentrations. 

Caffeine enhances the contractility of skeletal and cardiac muscle, and helps metabolize fat, thereby sparing muscle glycogen stores. It is also a central nervous system stimulant, which can aid in activities that require concentration. Many small studies using randomized, double-blind design have associated caffeine use with increased endurance times in athletes. - ... 

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