Robert De Niro triggered a trend when he gained 50 pounds to play an over-the-hill championship boxer in “Raging Bull.”

The gambit helped land him an Oscar, and ever since then Hollywood actors have dramatically tampered with their bodies to earn credibility on the screen.

Christian Bale pushes these boundaries to the limit in “The Machinist.” Surpassing scrawny to the point of being virtually skeletal, Bale chronicles the physical degeneration of a sleep-deprived, unstable factory worker.

The normally muscular star subsisted on a daily diet of an apple and a can of tuna for months at a time, resulting in a loss of 60 pounds. To go from the athletic build he revealed in 2002’s “Reign of Fire” then drop to 120 pounds for this role, then bulk back up to play the titular superhero in this summer’s “Batman Begins” — let’s just say that can’t be good for the ticker.

The transformation is rather distracting during the initial moments of “The Machinist.” Fortunately, there’s a method to the madness, and the dark psychological drama starts to resonate as the audience is gradually able to piece together clues of what is really happening.

“If you were any thinner you wouldn’t exist,” Trevor Reznik (Bale) is told by a prostitute he frequently visits (Jennifer Jason Leigh).

Reznik’s days are spent toiling as an industrial machinist, where any lack of concentration can result in instant amputation. His nights include a trip to an airport lounge for coffee, pie and flirtatious conversations with a beautiful waitress (Aitana Sánchez-Gijón).

Christian Bale portrays a sleep-deprived, emaciated man haunted by visions of his past in The

The fact that he hasn’t slept in a year isn’t helping his sanity. He starts obsessing about a sinister co-worker named Ivan (John Sharian) who doesn’t seem to be visible to his fellow employees. He also begins an ongoing game of hangman with an unknown partner who leaves Post-it notes in his kitchen. Then the refrigerator starts to bleed.

Director Brad Anderson made the ultra-creepy “Session 9” a few years back, which involved an asbestos removal crew that endured unpleasant events while cleaning an abandoned mental hospital. Anderson again proves himself versed in establishing an oppressive environment. Reznik’s world is a desaturated haven of greenish-yellow light and grimy corridors.

The Machinist1/2 Find showtimes, trailers and more on the movie

The fact the movie is set in a coastal American city but shot in Spain adds to the otherworldly quality.

Even the staunchest supporters of Anderson’s “Session 9” don’t bother to defend its letdown ending, so he pushes hard to steer “The Machinist” toward a satisfying payoff. Together with writer Scott Kosar (who penned the remake of “The Texas Chainsaw Massacre”), the pair succeeds in keeping the plot moving and the horrors mounting. The most memorable of these involves Reznik accompanying a friend’s kid to a theme park ride dubbed Route 666. This scene works fine as an unsettling diversion, but it gains weight in retrospect once the outcome of the character’s experiences are disclosed.

Unlike the spate of post-“Sixth Sense” films that go for a knockout finale at the expense of logic, “The Machinist” never cheats its audience. Anderson leaves plenty of hints as to what provoked Reznik’s mental and physical condition.

Admittedly, the twists the filmmakers come up with might have more impact if viewers never watched “Fight Club” or “A Beautiful Mind.”

This bleak exercise in paranoia is somewhat thin on “entertainment value,” but it’s heavy enough on mood to warrant spending a few hours inside Reznik’s skin.