What’s the fastest growing segment of health club members? It’s baby boomers. Membership at health clubs among adults 55 and older rose to 10 million from 1.5 back in 1987. “For the first time, we have a cohort of people who are just getting ready to retire and have an expectation of being physically active,” said Wojtek J. Chodzko-Zajko, an exercise scientist and expert in fitness at the University of Illinois at Urbana-Champaign.”