Trainer Tracy Anderson takes the concept of "tough love" to a whole new level.

Even the beautiful people don't get a free pass when it comes time for Anderson to whip her clients into shape: just ask Tracy Anderson Method devotee Gwyneth Paltrow.

PHOTOS: Gwyneth Paltrow through the years

After the 2006 birth of son Moses, her second child with hubby Chris Martin, Paltrow, 40, says she had an incredibly tough time shedding the baby weight.

"With my daughter [Apple, 8] it had been easier, but this time, no matter what I did, I felt stuck," Paltrow tells the January issue of Redbook (on newsstands December 18). "I couldn't shift the weight. But I met Tracy and she was this force from the second I met her."

PHOTOS: Gwyneth's amazing bikini body

During her initial evaluation with the fitness guru, "She pulled my pants off," the GOOP founder recalls. "I'll never forget it. She was like, 'Oh, my God, wow, I am just so surprised, because you look so good in clothes. I wasn't expecting this."

Despite the initial humiliation, the Oscar winner stuck with Anderson -- and says the expert's no-holds-barred approach paid off.

"[Working out with Tracy] did such wonders for my life, my confidence, my sex life, everything," Paltrow raves.

PHOTOS: Her surprise BFFs

Anderson agrees that her methods may be a little unorthodox, but her clients see incredible -- and love-life boosting -- results.

"When you feel your best, you're more confident in bed," Anderson explains. "It's not lights-out, under-the-covers sex. It's more like, 'Take a look at this!'"

This article originally appeared on Gwyneth Paltrow: Tracy Anderson "Pulled My Pants Off" When We First Met