Bodybuilders are a peculiar bunch. They’re extraordinary physical specimens, driven to sculpt their legs, biceps, shoulders and glutes into chiseled masses of impenetrable muscle.

Point a camera at them, though — as writer-director Vlad Yudin does for the engaging documentary “Generation Iron” — and these intimidating mountains of taut flesh reveal themselves to be charismatic, funny, passionate and totally aware of the unusual nature of their chosen lifestyles.

As narrator Mickey Rourke puts it: “They’re in a freak show, with no circus tent to hide away in.”

Yudin’s film is a direct relative of the 1977 hit “Pumping Iron,” which introduced mainstream audiences to the Mr. Olympia bodybuilding competition and helped transform Arnold Schwarzenegger into a household name.

The former “Governator” is one of many professionals — from competitors and trainers to judges — profiled by Yudin as he captures the pain and gain associated with bodybuilding in 2013.

Ironically, there is fat to trim from Yudin’s enlightening doc.

By choosing to focus on seven men in the 2012 Mr. Olympia competition, “Iron” occasionally repeats its points; these men take similar steps down the path to victory.

But “Iron” opens a window to an exclusive club and gives valuable insight into a small, dedicated and proudly unique community.