The original founder of 24 Hour Fitness, Mark Mastrov, is returning as owner and executive chair. 

Mastrov has partnered with private equity firm, LongRange Capital, to acquire the US chain and support the company's executive leadership team, led by president and CEO, Karl Sanft. 

Industry veteran, Mastrov grew the chain to 420 clubs and 4.5 million members, before selling it for $US1.6 billion in 2005.

In 2009, he led the purchase of Crunch Fitness with Jim Rowley and expanded it to 550 owned and franchised clubs before Leonard Green took a majority stake in 2025. He also founded UFC Gym.

"Mark founded and built 24 Hour Fitness into the powerhouse brand it is today, and the organisation is inspired and energised by his return," said Sanft. "With the business stronger than ever and our investments aligned with what members value most, this is the perfect time to welcome him back. Together with LongRange Capital, we're ready to accelerate our growth story."

24 Hour Fitness employs around 7,000 team members and is in the top three company-owned fitness clubs in the country. Over the past two years, an extensive remodel programme has been rolled out and a premium suite of offerings introduced, including Recovery24. 

New initiatives, partnerships and global expansion plans will be announced throughout 2026.

Bob Berlin, founder and managing partner of LongRange Capital, says: "24 Hour Fitness has an iconic legacy and significant opportunity ahead, and we're excited to partner with Mark, Karl, and the exceptional team at 24 Hour Fitness during this next phase of growth."

24 Hour Fitness offers premium strength and cardio equipment, turf zones, free weights, functional training areas, studio and cycle classes, personal training and a digital offering.

The company had a challenging pandemic, going into Chapter 11 bankruptcy in 2020 and shedding US$1.2 billion of debt when it reemergered in December of that year with new owners Cyrus Capital Partners, Sculptor Capital and Monarch Alternative Capital.

The three regrew the business, which had been slimmed down in the US, with locations in Singapore, China and Hong Kong being closed.

Mastrov now intends to accelerate global growth and it's thought may venture into franchising. All 24-Hour Fitness locations are currently owner-operated.

Mastrov has had a long career in the fitness industry with his New Evolution Ventures business, building multuple businese – some with celebrities, such as  Shaq O'Neal and Madonna. The latter ultimately wound down. He is acknowldeged as a pioneering entrepreneur in the sector.