What is the primary source of fuel for prolonged low-intensity exercise?

The primary source of fuel for prolonged low-intensity exercise is fats. During this type of exercise, the body relies on aerobic metabolism, which efficiently utilizes fat as a fuel source, especially when the exercise intensity is low. This is because fats provide a larger amount of energy (in the form of ATP) compared to carbohydrates or proteins when oxidized.

At lower intensities, the body is capable of sustaining prolonged activity primarily by burning fatty acids. These stored fats can be mobilized and transported to the muscles where they are metabolized to provide the necessary energy. Additionally, the availability of oxygen during low-intensity exercise further enhances the body's ability to utilize fat, as aerobic pathways generate energy without producing lactate, which can accumulate during higher intensity efforts.

Conversely, while amino acids and proteins can contribute to energy production, especially during extended periods of fasting or severe caloric restriction, they are not the body's preferred source of energy during low-intensity activities. Glucose, while important, tends to be more crucial during higher-intensity efforts where rapid energy is required, as it provides energy more quickly than fats. However, in the context of prolonged, low-intensity exercise, fats remain the predominant fuel source.