Final answer:
During long duration exercise, proteins provide about 5% of total energy needed by the body for cellular function and muscle repair.
Step-by-step explanation:
During long duration exercise, proteins can contribute significantly to overall energy transfer, providing about 5% of the total energy of total body requirement.
While carbohydrates and fats are the main sources for producing ATP (the cell's energy currency), proteins are mainly required for metabolic reactions that generate ATP and support muscle maintenance, growth, and repair. It is essential for athletes to consume adequate amounts of proteins to fulfill these functions, typically recommended at 1.2 to 2.0 g/kg/day.