What is the primary energy substrate during the initial minutes of exercise?

During the initial minutes of exercise, the primary energy substrate comes from phosphocreatine. Phosphocreatine serves as a rapid source of energy that is utilized in the first stages of physical activity, particularly in high-intensity and short-duration exercises.

When exercise begins abruptly, the body's demand for ATP (adenosine triphosphate) rises sharply, and phosphocreatine readily donates a phosphate group to ADP (adenosine diphosphate) to regenerate ATP. This process occurs very quickly and allows for the immediate supply of energy necessary for muscular contractions.

As exercise continues beyond the first few minutes, the body transitions to using carbohydrates (primarily in the form of glycogen) and fats as more sustainable energy sources. However, in those crucial first moments, phosphocreatine stands out as the most readily available and efficient source of energy, making it the correct choice in this context.