24 Hour Fitness Makes Mark Mastrov Interim CEO as Karl Sanft Departs

The change comes less than a year after Mastrov reacquired the gym chain he founded and scaled into one of the world’s biggest

Karl Sanft is out as president and CEO of 24 Hour Fitness, eight months after he steered the gym chain through a sale to founder Mark Mastrov, who is now stepping into the job himself on an interim basis.

“We can confirm that Karl Sanft is no longer with the company,” the chain told ATN in a statement, thanking him for his leadership and wishing him well.

It gave no reason for the exit and said it remains focused on members and staff of its roughly 240 clubs.

Mastrov, who founded 24 Hour Fitness in 1980s, reacquired the operator in January in partnership with private-equity firm LongRange Capital,

In a LinkedIn post, Sanft called his tenure an honor and seemingly referenced Mastrov’s return as a successful transaction that positioned the business for its next chapter. He added that his ties to the brand began more than 30 years ago as a member.

“It’s a company that has meant a great deal to me personally and professionally, and it always will,” he wrote.

Sanft’s exit is one of many this year. In just eight months, 2026 has already reset the leadership of much of the gym industry.

Crunch Fitness promoted president Chequan Lewis to CEO in June, moving longtime chief Jim Rowley to executive chairman. Vasa Fitness brought in former Portillo’s chief Michael Osanloo in March, as Rich Nelsen retired after eight years. 

Gold’s Gym named Brad Reynolds its sole CEO in July, scrapping a co-CEO model, PureGym elevated chief financial officer Alex Wood to CEO and Les Mills has named Jason Paris its new chief executive, who will take over in October.

Mastrov grew 24 Hour Fitness from one club into a 420-location chain with 4.5 million members before selling it in 2005 in a deal valued at more than $1.6 billion. He later helped lead Crunch Fitness and UFC Gym.