WHAT YOU DO: Work with ambitious athletes looking to get in peak form. This requires being tech-savvy enough to, say, analyze 3-D images of muscle movement, but most coaches insist on working with their clients in the real world. "I can be manic-depressive guy if I don't get my sun dose," says six-time Ironman champ–turned–triathlon coach Dave Scott, who spends mornings leading group runs or swim sessions.

WHY NOW: Membership at USA Triathlon has increased 531 percent in 15 years, adding nearly 80,000 multisport athletes, and there are now more than 300 domestic adventure races every year, up from two in 1995. The newbies can afford trainers, too: 35 percent of new cyclists own bikes worth $4,000.

THE NUMBERS: Hourly rates range from $70 to $300; a certified trainer charging $100 per hour can easily bring in $200,000 a year.

BREAKING IN: Develop a background in exercise physiology, kinesiology, or nutrition, and get schooled at any level via the national governing body of your sport, like USA Triathlon (usatriathlon.org). The two-year program at the National Coaching Institute Calgary (canadiansportcentre.com) is the only college of its kind in North America.