ISSA Nutritionist Exam 2025 – 400 Free Practice Questions to Pass the Exam

The preferred energy source for intense exercise lasting less than 30 seconds is the ATP-Creatine phosphate system. During short bursts of high-intensity activity, such as sprinting or heavy lifting, the body relies primarily on this system to rapidly produce ATP, which is the energy currency of cells.

The ATP-Creatine phosphate system is capable of providing immediate energy because it does not require oxygen and uses stored ATP and creatine phosphate in muscles to regenerate ATP quickly. This allows for maximum muscle output for a brief duration, making it ideal for intense efforts that last a very short time.

In contrast, aerobic glucose oxidation and aerobic fatty acid oxidation involve processes that require more time to generate ATP and are better suited for prolonged, less intense activities. Lactic acid fermentation, while it plays a role in longer bursts (around 30 seconds to 2 minutes), is not the primary energy source for the very first moments of intense exertion and can lead to fatigue due to the accumulation of lactate.

Thus, the ATP-Creatine phosphate system is crucial for sustaining those initial seconds of high-intensity exercise, making it the correct choice for this question.