LAS VEGAS — Mixed martial arts fighter Georges St-Pierre wasn't cheating with petroleum jelly when a trainer rubbed his shoulders and upper back between rounds of an Ultimate Fighting Championship bout, representatives for the middleweight said.

St-Pierre's cornermen, responding to a request by fighter B.J. Penn for an investigation by Nevada athletic regulators, said they did nothing illegal to affect the outcome of the Jan. 31 championship fight between St-Pierre and Penn in Las Vegas.

They said cornerman Philip Nurse rubbed St-Pierre's back between rounds as part of a breathing exercise to calm the fighter.

In a Wednesday letter to the Nevada State Athletic Commission, Nurse and lead cornerman Greg Jackson called the request for a probe "nothing more than Mr. Penn's desperate attempt to protect his reputation and commercial value after being totally dominated by a superior athlete."

Commission executive Keith Kizer told The Associated Press Thursday that the commission will take up the request on March 17. Disciplinary possibilities include a warning, fines or suspension.

A lawyer for Penn did not immediately return a phone call seeking comment.

St-Pierre dominated the fight and won after a doctor stopped the bout in the fifth round. But Penn's lawyer complained to the commission three days later about the slippery substance on St-Pierre's shoulders and upper back.

Nevada regulators are concerned whether the jelly could have prevented Penn — who is known for Brazilian jiujitsu — from performing grappling moves on St-Pierre.

In mixed martial arts fights, petroleum jelly is allowed to be used on the face, but nowhere else on the body.

Nurse said he never considered applying the substance anywhere except St-Pierre's face. He said he applied some jelly to the back of one of his hands, then used his fingertips to rub the jelly on the fighter's face — and nowhere else.

"I was not aware of, nor did I intentionally leave any of the lubricant on my hands when I began to conduct the breathing and relaxation technique on Georges," Nurse said in his letter. "Under the watchful eye of commission officials, in front of the cameras and the crowds, it would have been ludicrous for me to have 'greased' our fighter's back."

As part of their response, St-Pierre's representatives sent a video to the commission demonstrating Nurse using the technique on St-Pierre, but not from the Jan. 31 fight.

The video shows Nurse rubbing St-Pierre's chest and back in between rounds during two fights in 2008. It also shows a different trainer using the technique on St-Pierre before the fight in question, with St-Pierre wearing a shirt.