Carbohydrates are essential for sustaining performance in most competitive exercise, fueling both anaerobic glycolysis during high-intensity efforts and aerobic metabolism during prolonged activity. Numerous factors contribute to muscle fatigue and exercise performance; still, carbohydrate and muscle glycogen contents are agreed to have an essential role in sustaining prolonged exercise at moderate-to-high intensities. To maintain consistent training and competition performance, elite athletes under certain conditions consume adequate carbohydrates between sessions to restore liver and muscle glycogen and possibly supplement during prolonged workouts to delay depletion. Effective glycogen restoration requires both sufficient carbohydrate intake and adequate recovery time. Understanding how glycogen levels fluctuate during intense or prolonged exercise, the rate at which stores are utilized, and the optimal amount and timing of carbohydrate intake for replenishment is essential. Here we examine the role of carbohydrate availability and utilization in competitive cross-country skiing, which is characterized by exceptionally high whole-body energy turnover with varying loads on the upper- and lower-body muscles as well as fluctuating physiological demands determined by course profile, snow conditions, sub-technique, and race format. This narrative review synthesizes existing evidence on the role of muscle glycogen contents and carbohydrate intake in muscle function and fatigue mechanisms, with a particular focus on cross-country skiing and herein biathlon and Nordic combined. Additionally, we explore how exercise influences glycogen metabolism, the factors regulating glycogen utilization, and training adaptation in order to clarify physiological underpinnings and practical implications for endurance athletes.