Which mechanistic explanation best links caffeine ingestion to delayed fatigue during prolonged endurance exercise?

• A. Caffeine increases insulin secretion leading to immediate replenishment of muscle glycogen during exercise so the athlete does not deplete carbohydrate stores
• B. Caffeine acts purely as a diuretic to reduce body mass rapidly prior to endurance competition, which directly improves oxygen delivery to working muscles
• C. Caffeine blocks creatine kinase activity which prevents ATP breakdown and therefore preserves energy availability for the later stages of an endurance event
• D. Caffeine reduces the perception of effort while increasing reliance on fat oxidation, thereby sparing muscle glycogen stores and delaying exhaustion during prolonged exercise

Answer: (D)