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GRUNT & CENTER

He just can’t help the grunting.

Nor can he help shouting “Woo-woo!” or “Great song!” or “Good burn,” or – inexplicably, “You go, girl!”

That’s what a spin-class workout is all about, hedge-fund manager Stuart Sugarman testified yesterday, taking the stand as the victim in the bizarre case of an Upper East Side gym assault.

“These are words that would get me charged up and really come out automatically,” Sugarman, 48, told a jury, describing the prologue to a brutal spin-class smackdown that jangled his vertebrae and landed him in the hospital for 10 days.

“I try to get into the zone,” he explained of what both sides called his “vocalizations.”

Manhattan prosecutors say that because of his annoying hooting and bellowing, Sugarman was brutally tipped up and off his exercise bike last summer by an irate stockbroker.

His antagonist, Christopher Carter, had been sitting two bikes down at an Equinox gym at 85th Street and Third Avenue and was ticked off by the distractions.

Sugarman, 48, spent most of yesterday telling jurors of his ordeal at the hands of belligerent broker Carter, 44.

Carter is fighting a possible year in jail on the misdemeanor charges by arguing that Sugarman provoked the incident.

Along the way, jurors got a glimpse into the wacky, intense world of “spinning,” described by Sugarman and two others who were in that day’s class in almost religious terms.

Adherents try to achieve an ecstatic trance state – or get “in the zone.” The lights are dimmed, music throbs, and the instructor leads the class in call and response – “Are you ready? I can’t hear you!”

“There are times when 50 people will respond in harmony,” the spin instructor on that August day, Mark Selden, told jurors.

Both sides agree that Sugarman was loud – even Selden testified that Sugarman is the loudest “spinner” he’s ever heard in some 1,700 workouts.

“Isn’t it true that the frequency and volume of your vocalizations were the loudest in the class?” defense lawyer Michael Farkas asked Sugarman. “I try to get into it, yes,” he answered.

But opinions differed yesterday on what happened as the hedge-funder’s howling drove the berserk broker off his bike.

“He yelled at me to shut the ‘F’ up,” Sugarman told jurors.

“What was your response to that,” asked prosecutor Brigid Harrington.

“Like, at that point, my reaction was, like, ‘You’re kidding me, right?’ ” Sugarman answered, insisting that he himself never cursed, never flipped the broker the bird, and did absolutely nothing provocative.

This, despite cop testimony that Sugarman admitted giving Carter the finger and cursing, and testimony by another “spinner” that when Carter shouted, “Shut up,” Sugarman taunted, “Make me.”

Sugarman insisted he said nothing worse than “You don’t have to be such a baby.”

“Then I hear him say, ‘Did you call me an effin’ baby?’ Then he got off his bike and charged me like a football player would charge a training sled, and proceeded to lift my bike and I. The bike is about 150 pounds and I’m more than 200 pounds. He lifted the whole thing up and threw it and lifted it against the wall.

“He was looking up at me,” Sugarman remembered. “And he held me up over his head. He looked at me and very loudly said, ‘F’ you. And then he dropped me.”

Afterward, “He looked as though he was proud of himself.”

Immediately, Sugarman insisted, the pain in his neck was “excruciating” and “searing.”

But why did Sugarman continue the workout until the end of class for at least another 20 minutes before asking for an ambulance, asked the defense lawyer.

“I was trying to be macho,” he explained. “A football player plays through pain.”

laura.italiano@nypost.com