- The energy source that predominantly fuels brief, high-intensity muscle activity, such as a 100-meter sprint, is creatine phosphate.
- This is because creatine phosphate provides a rapid but short-lived supply of ATP, which is the primary energy carrier in muscle cells.

Here is why creatine phosphate is the main energy source in this scenario:
- During a 100-meter sprint, the muscle demands immediate and high amounts of energy within seconds.

- Creatine phosphate donates a phosphate group to ADP, quickly regenerating ATP without requiring oxygen, which is crucial for anaerobic conditions during maximal exertion.

- This system can sustain muscle contraction for approximately 10 seconds, perfectly suiting the duration of a 100-meter sprint.

- After the creatine phosphate stores are depleted, the muscle then relies more on anaerobic glycolysis for continued, but less immediate, energy production.

- Oxidative phosphorylation and fatty acid beta-oxidation generate much more ATP but at a slower rate and are more suited to prolonged, moderate-intensity activity rather than brief, explosive effort.

In summary, the creatine phosphate system acts as an immediate energy reserve to rapidly regenerate ATP, enabling muscles to perform brief, high-intensity tasks efficiently.

Reference: Guyton and Hall Textbook of Medical Physiology, 13th Edition, Chapter 65, Muscle Metabolism