24 Hour Fitness Founder Mark Mastrov Steps In as Interim CEO

Karl Sanft is no longer CEO of 24 Hour Fitness. Founder and executive chair Mark Mastrov will serve as interim CEO.

24 Hour Fitness said in a statement to Club Solutions, “We can confirm that Karl Sanft is no longer with the company. We are grateful for his leadership and contributions during his tenure, and we wish him all the best in his future endeavors. 24 Hour Fitness founder and executive chair Mark Mastrov will serve as interim CEO. 24 Hour Fitness remains focused on serving our members and supporting our team members across the organization.”

Mastrov returned to the company as owner and executive chair following an acquisition completed in partnership with LongRange Capital in January 2026.

Sanft was named president and CEO of 24 Hour Fitness in June 2022 after serving as interim CEO once Tony Ueber stepped down in December 2021. Sanft wrote the following on his LinkedIn page on August 19, 2026:

“Serving as president and CEO of 24 Hour Fitness these past many years has been an honor. I’ve had the privilege of helping guide the company through some incredibly challenging and transformative times, culminating in a successful transaction earlier this year that positioned the business for its next chapter.

I’m incredibly grateful for the leaders and team members I’ve had the opportunity to work alongside. Their resilience, passion, and commitment to helping people improve their lives through fitness have been inspiring.

My relationship with 24 Hour Fitness began more than 30 years ago as a member, long before I ever imagined I would have the opportunity to lead this great brand. It’s a company that has meant a great deal to me personally and professionally, and it always will.

I’m proud of what we accomplished together, grateful for the relationships built along the way, and excited to see what the future holds for 24 Hour Fitness.”