Final answer:
The primary energy system that supplies the body with ATP during longer durations of exercise is the Oxidative system.
Step-by-step explanation:
The primary energy system that supplies the body with ATP during longer durations of exercise is the Oxidative system. This system utilizes oxygen to break down carbohydrates, fats, and proteins in order to produce ATP. It is the most efficient energy system, but it requires a sufficient supply of oxygen and works best during aerobic exercise.
Learn more about Energy systems in the body