Which fuel is used most readily by the body during high-intensity physical activities?

During high-intensity physical activities, the body primarily utilizes carbohydrates as its main source of energy. Carbohydrates are quickly broken down into glucose, which can be used for immediate energy needs, particularly during activities that demand a significant amount of strength and endurance, such as firefighting. The rapid availability of glucose from carbohydrates supports activities that require explosive bursts of energy.

Other fuel sources, like amino acids, are generally used for energy during prolonged periods of low-intensity exercise or when carbohydrate stores are depleted. Saturated fats are slower to metabolize and primarily serve as a longer-term energy source during lower intensity activities. Starch is a form of carbohydrate, but in high-intensity situations, the body mainly relies on simple sugars rather than starches, which require additional processing. Thus, carbohydrates are indeed the most readily available and utilized fuel source during demanding physical exertion.