The body of a dead animal becomes very stiff in a condition called “rigor mortis”. which of the following is not a factor in the development of rigor mortis? calcium is released from calcium stores inside muscle cells. tropomyosin proteins do not block myosin binding sites along actin filaments. myosin heads remain bound to actin filaments after their power stroke. calcium binds to the troponin complex. lack of atp synthesis causes a failure of myosin heads to bind to actin filaments.