Answer:
This is true. As the intensity of exercise increases, the body relies more on fat as the primary fuel source for energy production. This is because fat is the most energy-dense source of fuel in the body, providing approximately 9 kcal per gram, compared to only 4 kcal per gram for carbohydrates. Additionally, the body's ability to oxidize fat increases at higher exercise intensities, allowing for a greater proportion of the fuel supply to come from fat. However, the body's ability to oxidize fat is limited, so at very high exercise intensities, carbohydrates become the primary fuel source.