OLD WAY
Rack up 3 sets of 8 to 12 reps every time you strength-train.

NEW THINK
Vary the sets, reps, and weight each session.

While the old approach will sculpt muscles, doing it day in, day out can get boring for you and your body. "Any time you add variety to your exercise program, you create a new way for muscles to adapt," says Len Kravitz, Ph.D., coordinator of the exercise science program at the University of New Mexico. And as they adapt, they get stronger. A number of studies have shown that periodized exercise programs—those in which you vary the sets, reps, weight, and/or rest times from workout to workout or week to week—yield better results than regular resistance-training routines, in which you usually change only the weight as you progress. To create your own plan that challenges your muscles in a new way every day, use the chart below.