Final answer:
Carbohydrates and lipids are the primary macronutrients used for energy during long-duration exercise. Carbohydrates are the main source of fuel, with intake recommendations ranging from 3-10 g/kg/day depending on exercise intensity. As exercise prolongs, the body shifts towards using lipids to preserve glycogen stores.
Step-by-step explanation:
During exercise of long duration, the macronutrients primarily used for energy are carbohydrates and lipids. Carbohydrates are vital as they are the main source of fuel for both the brain and muscle activity. The body stores carbohydrates as glycogen in the liver and muscle cells, but these stores are relatively limited. It is essential for athletes to consume a diet high in carbohydrates to increase their storage capacity. Athletes may need to intake about 3-10 g/kg/day of carbohydrates depending on the intensity and duration of the exercise.
As exercise continues and carbohydrate stores begin to deplete, the body increasingly relies on lipids for energy. This energy shift towards lipid utilization helps to preserve the remaining glycogen stores. Proteins also play a role, primarily serving as building blocks for body tissues, but may also be used for energy in prolonged exercise once carbohydrate and fat stores are diminished.