Carbohydrate during training is a performance tool, not a requirement for every session. For short exercise, glycogen is usually sufficient. As activity continues, maintaining blood glucose and supplying working muscle become more important.
The short answer
The need for carbohydrate during exercise depends mainly on duration, intensity, prior fueling, and performance goals; it is usually unnecessary for short sessions.
A time-based guide
Below about 60 minutes, water is commonly enough. For high-intensity activity lasting roughly 60–150 minutes, about 30–60 g carbohydrate per hour may help. Higher intakes in very long events require gut training and specialist planning.
Who benefits most?
Endurance and long team-sport athletes, people training twice a day, and athletes starting with low stores or racing for performance are more likely to benefit. A light 45-minute session usually needs no gel.
Find your dose
Start at the lower end and assess energy, performance, and gut symptoms. Drink concentration, heat, and water intake affect tolerance. Never try a new race plan on race day.
Practical checklist
Do not test unfamiliar food on an important training or competition day.
Adjust amount and timing to gut tolerance and session goals.
The quality of the whole daily diet matters more than one meal.
References
Nutrition and Athletic Performance — Academy of Nutrition and Dietetics, Dietitians of Canada and ACSM — https://pubmed.ncbi.nlm.nih.gov/26920240/
ISSN Position Stand: Nutrient Timing — https://pubmed.ncbi.nlm.nih.gov/28919842/