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

• A. Saturated fat
• B. Amino acids
• C. Starch
• D. Carbohydrates

Answer: (D)

Carbohydrates are the body's readily available fuel for high‑intensity effort because glucose can be released from glycogen and used quickly through glycolysis to produce ATP, even when speed is essential. Stored glycogen in muscles provides a fast local source of glucose that can fuel powerful bursts of activity. Fats, while energy-dense, take longer to mobilize and require more oxygen to yield ATP, making them less suitable for rapid, intense work. Amino acids mainly support tissue repair and can contribute energy only when carbohydrate supplies are low or during very prolonged activity. Starch is a dietary carbohydrate that must be digested to glucose, which is slower than using stored glycogen for immediate high‑intensity energy.