What happens to ATP during muscle contraction?

• A. ATP is converted to ADP when the phosphate is released, providing energy.
• B. ATP is stored unchanged during contraction.
• C. ATP is converted into glycogen for energy storage.
• D. ATP is produced from ADP during contraction.

Answer: (A)

Muscle contraction relies on the energy released when ATP is hydrolyzed. In the process, ATP is converted to ADP and inorganic phosphate, and that release of chemical energy powers the myosin head to perform the power stroke and move the actin filaments. The energy needed for contraction comes from this hydrolysis, not from storing ATP unchanged or turning it into glycogen. After the stroke, ADP is released and regenerated ATP is produced again through cellular processes to prepare for the next cycle. This is why the statement that ATP is converted to ADP when the phosphate is released, providing energy, best describes what happens during contraction.