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"Training for a new badass project," the mum-of-three wrote.
She went on to explain she had used her husband's fitness app and the expertise of British ultra-sea swimmer and adventurer Ross Edgley.
As well as pulling some seriously next-level moves in the gym, Elsa can be seen lifting weights, pulling a heavy sled and performing burpees between flipping a large tyre – all while Ross cheers her on.
In a second clip, Elsa can be seen crawling on all fours down the length of a house, while navigating a way around a black medicine ball as Ross shouts at her to do "one more".
It's not entirely clear what the new project is, but at the end of the second clip on Elsa's Instagram post, Ross' new book The Art Of Resilience slides across a table.
Ross is also currently training Hollywood star Chris up in NSW's Byron Bay, with an earlier post on the swimmer's Instagram account revealing the pair were completing monster workouts together.
"Civilise the mind … but make savage the body," he said on Sunday.
"Words CANNOT describe the strength & conditioning savagery that's going down in Byron Bay right now but I will state this …"
He continued: "In 2021 my brobarian of the barbell @chrishemsworth will bring a level of athletic conditioning to @marvel (and acting as a WHOLE) that's NEVER been seen before in the history of film-making."