NSCF Certified Personal Trainer Practice Exam

During prolonged endurance exercise, the body primarily relies on carbohydrates and fats for energy. However, protein can also play a role in energy metabolism, particularly when carbohydrate stores become depleted or in situations where there is insufficient caloric intake. In the context of long-duration activities, protein contributes to energy supply, potentially accounting for up to 15% of the body’s energy needs.

It’s important to recognize that, while carbohydrates serve as a quick source of energy and fats provide sustained energy, protein usually serves as a secondary source. During endurance activities, the body can utilize amino acids from protein as a means to produce glucose through gluconeogenesis, especially when glycogen stores are low.

The other options either do not contribute significantly to energy needs during endurance exercise (such as vitamins, which are crucial for metabolic processes but not direct energy sources) or serve different primary functions that are not specific to prolonged energy expenditure.