"The key to adding mass to any large muscle group, such as the chest, is varying the type of stress you put on it," says Michael Y. Seril, N.S.C.A.-C.P.T., owner of Michael Seril Fitness, a personal-training company in Orange County, California. "Try combining these two movements into one exercise," he says. It's sort of a "press-fly." The bonus: You'll save time, because you'll be doing more work with less rest between exercises.

Lie faceup on a bench, holding dumbbells with an underhand grip at the sides of your chest.

Press the weights straight up and rotate them until your palms are facing each other.

Keeping your elbows slightly bent, lower the dumbbells outward in an arc until they're at chest height.

Use your chest to pull them back up, following the same route in reverse. Lower the weights back to the starting position. That's one repetition. Perform three or four sets of eight to 12 repetitions.