INSIDE THE TYPICAL Foghat-themed weight room you'll find two typical users: bronzed apes getting ripped by hogging the bench, leg sled, and mirrors; and past-their-prime athletes hoping to cut an old squash injury off at the pass with a lazy machine circuit. Too bad. Not only are such routines mind- and soul-numbing, but because they're derived from bodybuilding—a dubious athletic niche that treats muscles as trophies rather than team members—both are fundamentally flawed. For the kind of usable musculature that may not seal the deal on ElimiDate but will sharpen your prowess on the trail, slopes, or river, it's time to embrace functional training, an approach to lifting that mimics movements actually involved in sports.

"You need to train in patterns that reflect life," says Paul Chek, the country's best-known functional-fitness evangelist. Chek developed many of the movement's tenets at his eponymous training center in Encinitas, California. Rather than isolating individual muscles, functional exercises follow the three basic motions of athletics (rotational, side-to-side, and front-to-back) to recruit entire muscle groups, and put you on your feet rather than a padded bench. When you're forced to maintain your balance while moving weight, you strengthen your core, an oft-neglected muscle group comprising your glutes, lower back, and abdominals. A solid core is vital for transferring power from lower body to upper body—like when lifting a 60-pound pack onto your back—or vice versa. "If your core is deficient," says Chek, "your arms and legs have nothing to anchor to."

Much to the weight-machine industry's chagrin, functional training has become more than the pet theory of a handful of personal trainers. The National Academy of Sports Medicine recently developed a functional-training certification program. And prior to the last two Olympics, U.S. athletes were using functional regimens to prepare for everything from triathlon to alpine skiing. "Ninety percent of our training involves movements that mimic sport," says Dana Healy, director of conditioning at the U.S. Olympic Training Center in Colorado Springs. "It makes more sense—how does a Nautilus curl transfer over to everyday activity?"

This month, in part two of our Shape of Your Life program, as you continue to build your endurance foundation, we'll introduce a functional-strength regimen for the gym. You'll start with only one set (studies show that one set, done right, has the same benefits as two). You'll put equal emphasis on the down portions of each lift, developing your muscles to descend, not just climb, a mountain. And when you plateau, you'll lift less weight for a day before attempting more—a periodization strategy you can think of as "step back and leap."

All this should be welcome news. By lifting less weight in a smarter fashion, functional training won't tap your endurance resources the way traditional approaches can. (Yes, you will be doing aerobic endurance work in month two). Most of the exercises you'll perform can be adapted; almost anything done on two feet, for example, can be done on one. This should help prevent workout boredom. And most important, you'll nurture real muscular movement for the field—not just the mirror. Which is the only kind of strength you'll ever need.