Steve Bogard's cholesterol was way up. His heart rate jumped with high exertion. Though not overweight, he wasn't in great shape.

Fast-forward 10 years.

The 56-year-old regulatory scientist at Eli Lilly and Co. recently went on a weeklong scuba-diving trip with whale sharks in Honduras and ran the Boston Marathon. Come July, he's competing in his first half-Ironman — 1.2-mile swim, 56-mile bike ride and 13.1-mile run — after doing shorter triathlons in recent years.

"I feel like I am pushing back Father Time," Bogard says. "This is the best shape I've been in in my life."

While Bogard's physical exploits are greater than the adventures of many his age, he has a lot of company among 43- to 61-year-old baby boomers — the fastest-growing segment of the health-conscious crowd. Fitness experts say more boomers are realizing they need a regimen of cardio, strength, flexibility and balance training to enjoy a long, healthy retirement.

Some prefer exercising on their own or joining teams. Others prefer help available at gyms or clubs. The International Health, Racquet & Sportsclub Association reports the number of members over age 55 in its 4,000 clubs climbed from 7.3 million to 7.9 million from 2000 to 2005.

Boomer classes also are popping up at gyms: In Indianapolis, there is Boomer Tai Chi for Arthritis and Boomer Low Impact Aerobics at the National Institute for Fitness and Sport, and the dance-aerobic F.I.T. 50 class at the Westview Healthplex Sports Complex, for example.

"Our baby boomers aren't letting themselves get to the point where they're out of shape," says Amy Rickelman, Westview's group fitness director. "Whenever they see the first changes to their bodies, they come in."

It's not just for stretching or water aerobics, although those are good options. They're taking more intense classes, such as spinning (cycling) and strength-building weight training.

"They come in to improve on their health, not just to lose weight," Rickelman says.

Deanna Dean-Webster, 48, an Indianapolis attorney, is one of them. She and her husband, David, 49, work out at Westview five or six times a week. She works with a personal trainer once a week and uses the treadmill or elliptical trainer.

She's noticed many positive side effects: more energy, tighter arms, abs and buttocks, and a better mood.

Perhaps the best upshot? The couple can be active with their two sons and daughter, with whom they play tennis, kayak and scuba dive. They even mountain-biked and zip-lined during a recent Alaskan cruise.

As boomers age, fitness industry experts are telling facilities to focus on the diverse needs of that age group, says Heather Benesh, NIFS program director.

This means offering classes to help people with arthritis and balance problems, such as tai chi, and low-impact aerobics, such as NIFS' Body Vive with low-weighted balls, tubes and weights.

And if boomers think they can ease up on exercising as they age, the American College of Sports Medicine and the American Heart Association beg to differ. Recently revised recommendations from the two groups say that daily fitness levels for all healthy adults ages 18 to 64 look the same: moderately intense cardio exercise 30 minutes daily five days a week, or vigorously intense cardio 20 minutes a day three days a week, plus eight to 10 strength-training exercises, 10-15 repetitions each, two to three times a week, as well as balance exercises

Former world-class long-distance swimmer Diana Nyad, who co-owns an online fitness program for women over 40 (www.BravaBody.com), says women are too often fixated on weight loss.

"They don't understand that yoga, Pilates, stretching, weight-lifting are what help you keep supple and young," says Nyad, 58. "That's what helps you feel better and you'll be able to do cardio exercising better, too."