What is the primary fuel source for a marathon?

The primary fuel source for a marathon is fat oxidation. During prolonged endurance activities like marathon running, the body predominantly relies on fat as a fuel source after the initial minutes of activity. Fat oxidation occurs in the mitochondria of cells, providing a sustainable source of energy for long-duration activities, especially once glycogen stores have diminished.

While carbohydrates are initially used as a quick source of energy, as the race continues and glycogen depletion occurs, the body increasingly turns to fat as a more abundant energy source. This transition is crucial for maintaining performance over the extended duration of a marathon, where the overall energy demand is high, but the pace allows for efficient fat utilization.

In contrast, anaerobic glycolysis is primarily used during short, intense bursts of activity, creatine phosphate serves as a very quick energy source for high-intensity, short-duration efforts, and while carbohydrate stores are significant, they deplete after several hours of endurance exercise. Therefore, understanding the role of fat oxidation is essential in the context of endurance sports like marathons.