Final answer:
During the steady state of extended exercise, the body primarily uses aerobic metabolism and fat metabolism as its energy sources. Fatty acids derived from fat reserves and a small amount of glucose are used to fuel the muscles during this type of exercise.
Step-by-step explanation:
During the steady state of extended exercise, the body primarily uses a combination of aerobic metabolism and fat metabolism to supply energy to the muscles. Aerobic metabolism is more efficient and produces larger amounts of ATP, making it the preferred energy source during low-intensity activities. Fatty acids derived from fat reserves in the body are the primary fuel source for steady-state exercise. Along with fatty acids, a small amount of glucose is also used during this type of exercise.