Which molecule is known as the primary energy source for muscle contractions?

ATP, or adenosine triphosphate, is the primary energy source for muscle contractions. During physical activity, muscle fibers require energy to initiate and sustain contractions, and ATP serves as the immediate provider of this energy. When muscles contract, they break down ATP into adenosine diphosphate (ADP) and inorganic phosphate, releasing energy that powers the contraction process.

While glucose is indeed an important energy substrate and is metabolized to produce ATP, it does not serve as a direct energy source for muscle contractions. Instead, glucose undergoes glycolysis and cellular respiration to generate ATP. Creatine is another molecule that contributes to energy production by helping regenerate ATP from ADP in a faster way, but it is not the primary energy source itself. Lactate is a byproduct of anaerobic metabolism and can be used as fuel but is also not a direct energy source for contractions. The crucial role of ATP in directly fueling muscle contractions distinguishes it as the primary energy source in this context.