Planet Fitness co-founder Mike Grondahl has stepped down as CEO of the company, replaced by partner Chris Rondeau, according to the company. Grondahl will continue as a member of the board of directors.

The announcement came Thursday as part of the company's official notification that Planet Fitness, Newington, NH, has partnered with private equity firm TSG Consumer Partners. Terms of the deal were not disclosed.

Mike Grondahl told Club Industry last November that the deal with TSG Consumer Partners was completed and that he, Rondeau and brother Marc Grondahl, also a partner, would retain 25 percent ownership of the company.

"I believe that now is the time to make this change as TSG works with our team on plans for the future," Grondahl said in a statement Thursday. "What Planet Fitness has accomplished is truly amazing. The future of the company is extremely bright. Chris Rondeau is the right man at the right time to oversee the company's continued growth."

Rondeau joined Planet Fitness in 1993 and has been a partner in the business since 2003, serving as head of operations.

"I'm very excited about our growth ahead and honored to be following in Michael's footsteps as CEO," Rondeau said in a statement. "He's been a great mentor and partner and a good friend. I look forward to working directly with TSG as we look to expand the brand. With more than 100 projected club openings in 2013, the future couldn't be brighter. Our company is stronger now than ever."

Planet Fitness, which opened its 600th club last month in Michigan, says it has 618 clubs and 3.8 million members. It currently is a sponsor for NBC's "The Biggest Loser."

TSG Consumer Partners, which has offices in San Francisco and New York, has more than $2.9 billion in equity capital under management. Past and present partner companies include vitaminwater, Smart Balance, PopChips, Muscle Milk and Yard House.

"We are excited about the appointment of Chris Rondeau as CEO and are looking forward to Michael's continued insights as a member of the board," TSG Managing Director Pierre LeComte said in a statement.