Which fuel source is predominantly used during low-intensity exercise?

During low-intensity exercise, the body primarily relies on fats as its predominant energy source. This is due to the fact that fat oxidation provides a higher yield of energy compared to carbohydrates and proteins, particularly when exercise is sustained at lower intensities.

At lower levels of exertion, the energy demands of the body can be met efficiently by breaking down fat stores, which are abundant in the body. This process is more oxygen-efficient and is sustainable over longer periods, making it ideal during activities like walking, light jogging, or casual cycling.

In contrast, carbohydrates are typically utilized during higher-intensity activities where the demand for quick energy is greater. Proteins are generally not favored as a primary energy source for exercise, as they play a more essential role in muscle building and repair rather than in energy production. Cycling, while it represents a form of exercise, does not classify as a fuel source.

Thus, the correct identification of fats as the major fuel source for low-intensity exercise aligns with the physiological responses of the body to different exercise intensities.