San Francisco ? Barry Bonds’ personal trainer was back in jail Monday, where he’ll stay until he agrees to testify before a federal grand jury investigating the Giants slugger.

Greg Anderson, found in contempt of court for his refusal to talk, could remain behind bars for more than a year while the grand jury investigates Bonds for perjury and tax evasion.

“Sometimes sitting in the cooler for a long time may have a therapeutic affect and may change his mind,” U.S. District Judge William Alsup said during the rancorous, hourlong hearing, after which authorities whisked Anderson into custody.

“Maybe in 16 months he will change his mind,” Alsup said, referring to the remainder of the grand jury’s term.

Anderson, who has appeared five times before two federal grand juries without answering pertinent questions, also was held in contempt of court for two weeks last month but was released when that grand jury’s term expired.

Mark Geragos, the trainer’s attorney, said he would appeal the judge’s order.

The name of New York Yankees outfielder Gary Sheffield re-surfaced during Monday’s hearing as an angry Alsup recited the questions Anderson refused to answer before the grand jury.

The questions included whether Anderson injected Bonds with steroids and “whether Anderson knows Barry Bonds or Gary Sheffield.”

Prosecutor Matthew Parrella told the judge the government also was investigating unnamed athletes associated with Anderson and said there was a “mountain of evidence” to form the basis of the questions asked of Anderson. Parrella said the evidence included documents seized at Anderson’s house in the BALCO investigation and from “testimony of other witnesses.”

The trainer already has served three months in prison and three months of home detention after pleading guilty to steroid distribution and money laundering in the investigation of the Bay Area Laboratory Co-Operative, which allegedly supplied Bonds and other elite athletes with performance-enhancing drugs.

On Monday, Alsup rejected Geragos’ plea that testifying before the grand jury would violate a deal Anderson struck last December to plead guilty in the BALCO case. Geragos said Anderson specifically stated he would not cooperate with the government as part of the deal.

At issue is whether Bonds lied under oath when he told the grand jury investigating BALCO in 2003 that he did not knowingly use steroids and that Anderson gave him what he believed to be flaxseed oil and arthritic balm.