Final answer:
During prolonged exercise, the body switches from using glycogen to fat as an energy source, which helps sustain endurance rather than increasing lactic acid production which is associated with high-intensity, short-duration exercises.
Step-by-step explanation:
During prolonged exercise, when the body starts using fat instead of carbohydrates (CHO), there tends to be a shift in the energy production pathway. This shift is from glycogen utilization, which is the body's preferred source of energy during high-intensity activities, to more abundant fat stores. Using fat as a primary energy source is an effective way to preserve glycogen stores and can help sustain endurance during prolonged physical activities.
As prolonged exercise continues, glucose becomes more important as the intensity increases. Fat continues to fuel aerobic metabolism, but if glycogen (stored glucose) levels start to run low, this can lead to muscle fatigue. Adequate oxygen delivery and the body's ability to sustain aerobic metabolism are crucial for using fat as fuel. It is important to note that using fat for energy does not increase lactic acid production, as it occurs predominantly during anaerobic metabolism, which is associated with high-intensity, short-duration exercises.