If you think about apples when you hear "core,"you're missing the ball. The core of the body, which contains the abdominal and spinal muscles, is the body's center for strength and stability. If your core is weak, your overall strength is compromised. If you can't maintain proper posture and position while exercising, you limit your ability to progress, and you risk injury.

Fortunately, it's easy to integrate exercises designed to fortify your core with other strength moves. By working multiple muscles at once, you can get a lot of work done in a little time. And you won't skimp on results.

The following workout, which should take you less than 15 minutes, integrates core training with exercises for the biceps and triceps. If you have more time, combine these exercises with last month's workout for the hips, back, butt, and thighs.

Gin Miller, creator of step aerobics, is a Reebok Master Trainer. She can be reached via our Web site or hers , www.ginmiller.com.