Final answer:
ATP molecules are present when a muscle is in a relaxed state according to the sliding filament theory.
Explanation:
According to the sliding filament theory, ATP (adenosine triphosphate) molecules are present when a muscle is in a relaxed state. ATP is essential for muscle contraction and relaxation as it provides the energy needed for the cross-bridge cycling process where myosin filaments walk along actin filaments, leading to muscle contraction.
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