The New Fitness Rules

When Should You Do Ab Exercises?

Old school: Save toning your abs for last.

New rule: Engage your core throughout your workout.

Cranking out crunches after a workout is so last millennium. "The core's biggest job is to provide a solid foundation for your extremities to work off of, so about 70 percent of your core training should be geared to strengthening the abdominals and lower back as stabilizers," says trainer Joe Dowdell, owner of Peak Performance gym in New York City. That means doing more exercises that require you to stiffen your core as you work against resistance -- such as doing planks or trying to keep your body from rotating as you pull a resistance band. "Exercises that strengthen the abdominal walls not only improve performance but also help reduce injuries," notes Stuart McGill, PhD, a professor of spine biomechanics at the University of Waterloo. To fill that remaining 30 percent of ab time, Dowdell recommends alternating in a few moves, like cable wood chops or medicine ball rotational throws, that work your core in a more integrated manner rather than just isolating its muscles with various crunches.