Barrier #1: You skip workouts due to "unforeseen conflicts."
Breakthrough: Exercise in the morning.
Consider these two benefits of a daybreak sweat session: You'll jump-start your resting metabolic rate, helping you burn more calories throughout the day; and you'll be less likely to have family, a job, or other obligations derail your workout. "The number-one excuse people have for not working out is time." says Rob Skinner, director of sports nutrition for the Georgia Tech Athletic Association. "Well, everybody has time early in the morning, and that way you get it done."

Barrier #2: You can't rely on yourself for motivation.
Breakthrough: Find a partner.
According to a 1999 weight-loss study undertaken jointly by the Universities of Minnesota and Pittsburgh, those who exercised with friends rather than alone boosted their chances of sticking with a program. Working out with a buddy adds accountability and provides a lift when you're not on top of your game. "I find it essential to have good training partners," says Roland Green, the 2001 overall World Cup mountain-bike champion. "To train by yourself, it becomes tough to maintain quality. But if you're in a group, someone is always feeling good that can push the pace."

Barrier #3: You get tired of the same old routine.
Breakthrough: Vary the place—and the way—you work out.
Sure, your lakeshore running trail is heartwarming for the first month. But then comes that fateful morning when the wildlife seems not quite as friendly, the water not so shimmery. "Every day of the week I ride and run a different route," says Tim Deboom, last year's Ironman World Champion. "It makes it impossible to get bored during my training." Take it from Tim, arguably the most highly motivated human on the planet: Mix up your workout venues and aerobic activities. Been trail running? Try road biking. You're a cyclist? Start swimming.

Barrier #4: You don't make it an adventure.
Breakthrough: Establish a goal beyond the weight room.
This week, dream up a giant fitness goal for October—a weeklong mountaineering trip in the Cascades, say, or your first trail marathon in Colorado—and post it on your refrigerator. By that time, the SYL plan will have you firing on all cylinders—and no glance in the locker-room mirror will motivate you like a looming, butt-kicking physical challenge.