Flex is a Pre-Match Action, which is the exact Pre-Match Action that Zeus uses.
"READY": Robot raises arms from the side.
STAT SCREEN: Menacing standstill, while staring at the screen.
BEFORE MATCH: Robot raises arms and looks around the ring.
"BELL": Robot lowers arms and changes to fighting pose.
AFTER MATCH: Robot lightly pounds chest with right arm, then both arms, then does Zeus' signature move.