Which energy system does a marathon runner rely on the most?

A marathon runner primarily relies on cellular respiration for energy during their long-distance race. This system utilizes oxygen to produce ATP, which is the energy currency of the body, and it is essential for endurance activities like marathon running. Cellular respiration includes both aerobic glycolysis and the Krebs cycle, allowing for sustained energy output over extended periods, such as the several hours it typically takes to complete a marathon.

In the case of marathon running, the body predominantly oxidizes carbohydrates and fats, generating energy efficiently while minimizing the accumulation of fatigue-causing byproducts. This is crucial for maintaining performance and endurance throughout the race.

The other energy systems, such as the ATP-PC system and the lactic acid system, are utilized for shorter bursts of activity and cannot support the prolonged demands of a marathon. The ATP-PC system provides quick energy for activities lasting up to about 10 seconds, while the lactic acid system kicks in during high-intensity efforts lasting from around 30 seconds to a few minutes. Neither can sustain the energy needs of a marathon runner, making cellular respiration the vital system for this kind of endurance sport.