There is a lesson to be learned from the trial of Christopher Carter, who is charged with the misdemeanor assault of a fellow cyclist in his gym’s spinning class: Some gym members should skip the group class and work out on their own.

On a summer night last year, the Studio Cycling Room at the Equinox Fitness Club on 85th Street and Third Avenue became the scene of a crime, prosecutors say, after two men, each ill-suited for group exercise in his own way, clashed over the appropriateness of making noise during a strenuous workout.

For Stuart Sugarman, 48, any amount of noise goes. From the witness stand in Manhattan Criminal Court yesterday, Mr. Sugarman told a jury about grunting during a good workout and releasing exclamations of “you go girl,” and “great song.”

“Are you psyched?” an assistant district attorney, Brigid Harrington, asked Mr. Sugarman, in an effort to explore his mind-set during spinning class.

“I am,” Mr. Sugarman said.

The evidence suggests that Mr. Carter, a stockbroker, preferred a quieter workout than Mr. Sugarman was prepared to allow his fellow cyclists. Mr. Carter wasn’t the only one who wished Mr. Sugarman would quiet down. Even the prosecution’s first witness, Sherri Sandel, who pedaled next to Mr. Sugarman, said she found his constant noises annoying.

Still, Dr. Sandel said she was frightened at how Mr. Carter responded to the annoyance. First he cursed at Mr. Sugarman. Then he got off his bicycle to go talk with a class instructor about getting Mr. Sugarman to quiet down. Finally, Dr. Sandel testified, Mr. Carter went over to Mr. Sugarman’s bike and lifted the front end off the ground, then dropped it back down, with Mr. Sugarman atop it all the while.

“Had you ever seen anyone act so aggressively in spin class before?” Ms. Harrington, the prosecutor, asked.

“No,” Dr. Sandel testified.

Mr. Sugarman said he hit the wall behind him hard when Mr. Carter lifted up his bike. Although he continued to pedal throughout the remaining half-hour of the class, Mr. Sugarman said his body grew numb.

“I was in shock,” Mr. Sugarman said. “I was in searing pain but I didn’t know what to do.”

He continued a little later: “The class is mostly women and it’s pretty embarrassing for a guy who is athletic to have this happen to him.”

Mr. Carter, who faces as much as a year in prison if convicted, did not testify yesterday.

After class, Mr. Sugarman called both the police and an ambulance to the gym. He stayed at Lenox Hill Hospital for the next two weeks undergoing surgery there for his injuries. He has since had to give up sports, he said.

One of the doctors he saw at the hospital, coincidentally, was well-acquainted with the cause of his injury: Dr. Sandel, his spinning partner, prepped him for surgery.

“He seemed to be in a lot of pain,” Dr. Sandel said of Mr. Sugarman.