Final answer:
During aerobic exercise, there is initially an increased utilization of carbohydrates, followed by enhanced fat metabolism as exercise continues, especially at low to moderate intensities.
Step-by-step explanation:
The fuel metabolism adaptations of aerobic exercise involve a complex interplay between carbohydrate and fat utilization. Initially, during periods of increased exertion, muscle glycogen is broken down to glucose, which is then used in glycolysis and the Krebs cycle to produce ATP. As the exercise continues, especially at low to moderate intensities, the shift towards increased fat metabolism occurs, becoming the predominant fuel source as muscle glycogen stores deplete. At this point, fatty acids are mobilized from adipose tissue to fuel aerobic exercise. A small amount of amino acids can also be used, particularly during long endurance activities.