Which energy system is primarily utilized by a marathon runner during the race?

Marathon runners predominantly rely on the slow oxidative energy system during the race because this system is designed for endurance activities that require sustained energy over an extended period of time. The slow oxidative fibers, also known as type I muscle fibers, utilize aerobic metabolism to produce energy. This means they utilize oxygen to convert fats and carbohydrates into energy, which is ideal for the prolonged, steady effort seen in marathon running.

The slow oxidative system is efficient in generating energy over long durations, which aligns with the demands of a marathon that typically lasts several hours. It allows runners to maintain a steady pace without fatigue, which is crucial for completing a marathon effectively.

In contrast to this, the other energy systems are not as suited for the long duration and continuous effort required in a marathon setting. For example, anaerobic glycolysis and the creatine phosphate system primarily support short bursts of high-intensity activity and would deplete quickly, while the fast oxidative fibers, although more suited for speed and power, still do not endure for the extensive distance required in a marathon. Hence, the reliance on the slow oxidative system is integral to a marathon runner's performance.