Although the text of your question is incomplete, we can affirm that the reasoning behind the carbohydrate loading is that if an individual increases the amount of carbohydrates that he or she ingests, he or she will have more energy and will be able to perform activities that require a lot of effort physical, with less fatigue.
Carbohydrate is an energetic molecule, as it provides fast energy to our body. Carbohydrate can be acquired through food, mainly in pasta, sweet potatoes, rice, cassava and other foods.
the more carbohydrates a person eats, the more fast energy that person will have and that is the basis of the reasoning behind the carbohydrate loading.
The carbohydrate loading is the term that refers to a type of diet practiced by athletes who participate in exercises that require a lot of resistance, such as marathon runners, for example. This diet consists of greatly increasing the intake of carbohydrates, allowing the athlete to have a lot of body energy and be able to finish his activities with less tiredness. However, this diet is very controversial, first because there is no scientific proof that it works and because the amount of carbohydrate it requires is very difficult to achieve.