A woman’s undercover operation at a Chelsea workout club gives a whole new meaning to the term “gym rat.”

The luxury West 17th Street condo that houses the Brick CrossFit gym on its ground level sent the spy in posing as a customer to bust instructors violating a court order that barred them from dropping free weights on the floor and causing other bad vibrations.

A lawyer for The Steiner Building at 257 W. 17th St. dispatched their undercover agent into the gym four times between September and December 2016, allegedly catching instructors breaking the rules — and now they’re asking a judge to fine the facility “a substantial sum” for the violations.

“We were getting complaints. It just seemed like the easiest way to figure out what was going on down there was to send somebody,” the residents’ lawyer, R. Jay Ginsberg, told The Post.

So he hired resident Ariele Krantzow, 31, who he described as a “civilian, not a trainer,” to investigate the clean-and-jerks.

At a 7:45 p.m. weights-based CrossFit class led by an instructor named Josh, Krantzow “observed several individuals…standing at the weightlifting platforms and repeatedly using and then dropping weights from heights as high as their shoulders and head.”

She said the weights reached 325 pounds and caused “noticeable sound and vibration in the gym” when they smashed to the ground.

Those activities violated a 2015 settlement between the condo and the gym that barred workout warriors from a “clean and jerk” training regimen that involves lifting barbells above the head and then dropping them to the ground.

The exercise enthusiasts were also supposed to do the workouts over shock-absorbing materials called “rogue pads,”—which Krantzow said were noticeably absent.

The racket from the gym had gotten so bad in the past that a Manhattan judge shut the place down in 2015 for causing “a daily assault on the quiet enjoyment of their apartments.”

That restarted over the past year with residents griping that the “thunderous” noises have woken them from sleep at 6 a.m. and rattled their furniture at night.

Jeffrey A. Kaplan, attorney for the gym, said his client is not violating the settlement and suggested that the residents were the ones running afoul of the agreement.

“There was nothing in there about sending in spies,” Kaplan quipped.

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