Create an image of a strength and fitness in your head. The first thing that springs to mind is probably an arm curled, biceps bulging with barely restrained power, but a more realistic and useful symbol might be a flat stomach.

The abdominal muscle group is literally the center of the body, making up the middle of what those in the exercise business call "the core," those muscles attached directly to the spine: the shoulders, the hip flexors and the abs--the transverse abdominis (TA), the rectus abdominis and the internal and external abdominal obliques.

It's their location at the center of the body that makes ab strength so important to good health, says exercise physiologist Connie Chamberlain.

"If your abdominal muscles are strong--the deeper layers-- your posture is more efficient," she said. "It helps with speed, helps with quickness, helps with balance and definitely injury prevention."

For the athlete, weekend or otherwise, abdominal strength means greater overall strength and efficiency on the field; for older adults it aids balance, which can mean avoiding injuries and falls; and for everyone in general, ab strength improves appearance with better posture.

"We live in such a ‘forward' world--computers, kids, groceries, whatever--you end up in a forward posture over time," said Chamberlain.

Lack of core strength and control means added pressure on the spine, which is forced to hold up the body when the muscles can't. The spine, though overtaxed, seems loose, the pelvis slumps forward and the body ends up in what Chamberlain calls a "lazy stance." Core strength counteracts this and can even help maintain the space between the bones of the spine, loss of which is a major cause of shrinking due to age.

"You look tall. You look slim--strong from the inside out," said Chamberlain. "Definitely a younger look."

Lisa Klein, one-time personal trainer at Gold's Gym, Venice and now co-owner of Pilates Plus, agrees abdominal and core conditioning definitely improves appearance.

"It makes your stomach look smaller," she said. "The TA's what defines the waist."

Here's the bad news: to make that six-pack pop takes something more than just exercise.

"To make them show up, it's a body-fat issue," said Klein, who encourages her clients to perform cardio-vascular exercise and practice good nutrition along with strengthening. "You have to think about what your goal is. Are we talking about strength or being able to see [the abs]. That's two different things. Certainly you get better results with diet and cardio."

Klein, whose personal training experience includes work on movie sets such as Titanic, recommends following the American Heart Association's recommended minimum 25-30 minutes of cardio-vascular exercise daily.

Besides a routine of strengthening exercises that improve functionality, Klein also encourages ab-friendly behavior all day. At the Pilates Plus office, employees use chairs built around exercise balls to help maintain posture. In the car, Klein keeps the seat in an upright position that forces her to sit up straight with her head and shoulders directly in line above her spine. At the gym, she does as many exercises as possible using her core muscles for support, such as dumbbell chest presses done on an exercise ball instead of a bench.

"Why use a bench when you can be the bench?" Klein asked.

Try Klein's total ab workout in just three exercises.