How yoga and Pilates are used therapeutically supports [Ralph La Forge]'s beliefs. Yoga therapy is incorporated in rehab programs for diseases and chronic conditions to help manage symptoms and improve quality of life. Pilates in a physical therapy setting helps people bounce back from injuries.

When it comes to structure, "Pilates is done in sets and reps, and yoga is not," says Leigh Crews, a Georgia-based yoga instructor and former Reebok program developer in yoga and Pilates. "Pilates is a very ordered and structured way to exercise. So people need to figure out if they want an instructor counting reps and leading them through a very organized series of exercises, or something a little more free-form. Yoga does have a built-in structure, but it isn't built so much around numbers."

Some instructors notice that certain personality types are drawn to yoga or Pilates. "If someone is more comfortable being in a contemplative state, or at least with an inwardly directed focus, they'd probably gravitate more to yoga," says Elizabeth Larkam, a San Francisco Pilates instructor and spokeswoman for the American Council on Exercise. "If someone is more accustomed to looking outward and addressing external stimuli, then they probably would be more at ease with Pilates."