Zac Efron I Know the Ropes

3/6/2016 6:18 AM PST BY TMZ STAFF

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Zac Efron was put through the paces Saturday, wearing his signature not-much-at-all.

Zac's in Miami filming the "Baywatch" movie and it looks like next stop was the ocean, because he's wearing a patriotic Speedo under his shorts.

He climbed a rope, navigated a tire obstacle course ... who are we kidding -- he's not wearing a shirt.