Movie musclemen Arnold Schwarzenegger and Sylvester Stallone quivered and caved after getting calls from a supermarket tabloid, a private investigator claims.

A National Enquirer reporter boasted that she got a one-on-one interview with Schwarzenegger, now the governor of California, after editors threatened to run a story on rumors that he slept with Brigitte Nielsen. The two co-starred in the 1985 leather-kilt epic “Red Sonja,” and Nielsen married Stallone five months after the film’s release.

Turns out the reporter herself was being recorded by a writer at The Globe, Jim Mitteager. “That’s how I got Schwarzenegger,” The Enquirer scribe crows on tape.

Stallone later had his own problems with the paper. The Enquirer reporter is heard to say that Stallone handed over personal information after the paper obtained nude photos of him taken from the set of “The Specialist,” a steamy thriller co-starring Sharon Stone.

The tapes were unearthed by investigator Paul Barresi for his book on life as a legman for notorious Hollywood P.I. Anthony Pellicano. Reps for Schwarzenegger and Stallone told us they did not recall such events.

Reps for The Enquirer declined to comment.