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Ronda Rousey busted her ass this weekend -- pounding the sand at the dunes in Malibu in a crazy workout session.

Question is ... is this comeback training or is she just staying in shape?

Ronda is currently taping "Battle of the Network Stars" (she's one of the team leaders) and part of her job is navigating the obstacle course. We saw her run the course last week -- she looked pretty good.

But now, with the UFC legend running the insanely challenging dunes at Malibu ... ya gotta wonder if there's even the slightest chance she's trying to get back into fighting shape.