Isaacs was running the workout facility at the complex and had offered to train the woman, who was a tenant in the building, according to LAPD Det. Geoff Tovares. Issacs allegedly assaulted her in his office some time during the training.
He is a professional trainer who advertises weekend training retreats and training to help actors get in shape for their roles. His client list includes Clint Eastwood, Kurt Russell, Goldie Hawn, and Lance Armstrong.
The Los Angeles County District Attorney's Office has filed felony charges against Isaacs, who is free on $250,000 bail.
Investigators said Isaacs had used a similar approach with a woman several years ago.
"It's very similar, where he had offered to do some training with this other woman and took advantage of her," said Tovares.
Isaacs pleaded guilty to a misdemeanor in that case.
Detectives believe there may be other women he victimized who have been afraid to come forward. Anyone who believes they were assaulted by Isaacs or who has any information about an assault was asked to contact the LAPD sex crimes division at (213) 473-0447.