Which energy system possesses the greatest capacity for ATP production?

The oxidative energy system possesses the greatest capacity for ATP production due to its reliance on aerobic metabolism, which allows for sustained energy output over longer periods. This system utilizes carbohydrates and fats and can generate a large amount of ATP when oxygen is available, making it highly efficient for activities that require prolonged endurance, such as running or cycling.

In contrast, the phosphagen system primarily provides immediate energy through the breakdown of phosphocreatine and is limited in duration, usually supporting high-intensity efforts lasting only a few seconds. The glycolytic energy system, while also capable of producing ATP quickly, does so anaerobically and leads to the accumulation of lactate, which can limit performance over time. The term "fuel reserve" refers more generally to the substrates available in the body for energy rather than a specific energy system, so it does not directly describe ATP production capacity. The oxidative system's ability to tap into larger fuel reserves and sustain energy production over extended durations is what makes it the best choice regarding ATP capacity.