"Follow your passion" is pretty standard advice for entrepreneurs. Dick Costolo is adhering to it in his post-Twitter life.

Seven months after he stepped down as CEO of the social-messaging service, Costolo on Monday  revealed that he's launching a new company: "a software platform that reimagines the path to personal fitness." His partner in the new venture is Bryan Oki, former director of a Bay Area CrossFit gym and most recently co-founder of a health and wellness consultancy called Fitify.

"This platform will go beyond measurement to motivate and drive improvement and make the road to personal transformation fun and social," Costolo said in a note he posted to Twitter. "For wellness professionals, from fitness coaches to physical therapists and nutritionists and more, our platform will be the easiest and most flexible way to extend expertise and guidance by orders of magnitude."

Even by the standards of the Bay Area, where every other executive you meet is a competitive cyclist or dedicated rock climber, Costolo qualifies as a fitness fanatic. At age 52, he's built less like a technology executive than like a slugging left fielder. When I interviewed him last year for the cover of our March 2015 issue, he told me his punishing workout routine--alternating sessions of CrossFit and SoulCycle on weekdays and biking in the Marin County hills on the weekends--was integral to his ability to run a large, fast-changing organization.

"Everybody in the company's working a very large number of hours on any given week, and doing things like this gives you the energy to grind through all that and not be completely worn down and unhealthy," he said.

Costolo used to run distances, but found it didn't provide enough of a mental break from his job, so he switched to higher-intensity pursuits. "The positive aspect of the workouts that I do is my mind is 100 percent solely cleared during that workout, because I can't think about anything. There are no random thoughts and distractions coming into my mind when I'm doing some crazy...workout in CrossFit, or cycling up Mount Tam on Eldridge Grade, and trying to go as fast as I can in granny-gear. Your mind is totally clear. You're like, 'I gotta get up without falling off the edge of this bike.'"

Costolo is also a big proponent of bringing employees together in fitness classes to promote bonding, especially among those who might not have a chance to interact at work. "It's one thing to hear it from the head of the department and it's another thing to see these people during an hour within the work environment but not doing actual work and know, 'Oh yeah, I know that person in engineering. They were great, they were super helpful in that weight-lifting thing we were doing,' or whatever it was. It humanizes these other departments and helps people realize, 'Yeah, there are lots of people working really hard in these other organizations that we don't even know anything about.'"