ISSA Strength and Conditioning Certification Practice Exam - Prep & Study Guide

The energy source required for the cross-bridge cycle is ATP hydrolysis. During muscle contraction, myosin heads bind to actin filaments to form cross-bridges, and this process is powered by the hydrolysis of ATP. When ATP is broken down into ADP and inorganic phosphate, it releases energy that is used to power the power stroke of myosin, pulling the actin filaments toward the center of the sarcomere, which ultimately leads to muscle contraction.

ATP binds to the myosin head, allowing it to detach from the actin filament, and then its hydrolysis occurs, providing the necessary energy for the myosin head to pivot and reattach to a new position on the actin filament to continue the cycle. This process is essential for sustaining muscle contractions during physical activity.

In contrast, creatine phosphate serves as a rapid source of energy for ATP regeneration, but it does not directly participate in the cross-bridge cycle itself. Glycogen acts as a storage form of glucose and can be broken down to provide glucose for ATP production, but it is ATP that directly fuels the cross-bridge cycle. Fatty acids are utilized primarily in aerobic metabolism for longer-term energy production but are not directly related to the immediate energy