Hard to The Core; Increasing the strength of the torso isn't a fitness fad, it's one key to healthier aging--and can even help active folks stay injury-free.

Byline: Peg Tyre and Jennifer Barrett

David Burnes was on a walking tour of Madrid last fall when the low-grade discomfort he'd been feeling in his back for weeks morphed into molar-grinding pain. Burnes, 50, realized he needed serious medical attention and cut his trip short. Back in the United States, he was diagnosed with a ruptured disc and, after rejecting surgery, was sent for intensive physical therapy. Burnes, the CEO of a Massachusetts software firm, was unimpressed at first by the stretching, crunches and leg lifts he had to do. "It seemed like the stuff girls do," says Burnes, who biked, skied and worked out with weights before his back problems slowed him down. But after 20 minutes of sweating and grunting, Burnes had a revelation. "These instructors," he admits with a laugh, "were kicking my butt."

Actually, they were strengthening his core muscles. And what Burnes and millions of other boomers are discovering is that a strong torso, though hard-earned, is essential for long-term…