The primary energy source utilized by muscles during short bursts of activity is adenosine triphosphate (ATP). ATP is produced rapidly during high-intensity exertion, primarily through anaerobic energy pathways. Creatine phosphate also plays a critical role in regenerating ATP. This source provides immediate energy for high-intensity activities, such as sprinting or weightlifting. However, ATP stores are limited and deplete quickly, necessitating a shift to other energy systems for sustained activity.