Which statement best describes the energy source implicated in the completion of rigor mortis?

• A. Exsanguination
• B. Depletion of creatinine phosphate
• C. Depletion of glycogen
• D. Degradation of the z-line structure

Answer: (B)

Rigor mortis happens because ATP in muscles runs out after death, so the cross-bridges formed during contraction can no longer detach. The rapid ATP supply after death comes from the creatine phosphate pool, which donates a phosphate to ADP to regenerate ATP. When creatine phosphate is exhausted, ATP cannot be replenished, cross-bridges remain locked, and rigor is completed. So the energy source implicated in the completion is the depletion of creatine phosphate. Explanations of the other options don’t fit because they’re not the immediate energy reservoir driving the postmortem stiffening, whereas the process is fundamentally about the loss of creatine phosphate–generated ATP.