"Kimberly Bell, a former mistress of Barry Bonds, is expected to take the witness stand in the slugger's perjury trial Monday and give graphic testimony about changes she observed in the slugger's body at the peak of his home run prowess.

The government's pre-trial filings say that Bell, who posed nude for Playboy in November 2007, will testify that beginning in 2000 she observed Bonds with "bloating, acne on the shoulders and back, hair loss and testicle shrinkage" - all documented side-effects of steroid abuse. Bell is also expected to say Bonds told her about his steroid use and suffered from steroid-fueled rages.

Her testimony will likely be subject to vigorous cross-examination from the attorneys defending Bonds from charges that he lied to a grand jury investigating the BALCO doping ring in 2003 when he said he didn't use steroids or human growth hormone.

Bonds attorney, Allen Ruby, has already attacked Bell's credibility in the week-old trial, devoting part of his opening statement to painting Bell as embittered by her breakup with Bonds, who gave her money for payments on a house in Arizona.

Other witnesses the government plans to bring to the stand this week include IRS agents Mike Wilson and Ana Geter, former Giants trainer Stan Conte, and the team's equipment manager, Mike Murphy, who prosecutors have indicated will testify that Bonds' cap size grew while he was with the team."