Want to look slimmer without doing any "real" work? How about getting rid of back and neck pain? It all starts with one simple thing: posture. We talked with a few posture experts, and here's what they had to say:

Why is good posture so important?

Nothing ages you faster than a stooped posture. A strong, straight spine portrays youth and vigor, says Janice Novak, author of "Posture, Get It Straight!" (www.ImproveYourPosture.com). Slumping decreases your chest measurement, narrows your shoulders and can decrease your height by up to 2 inches.

And finally, posture is the single most important factor in the health of your back and joints. According to the National Institutes of Health, poor posture and body mechanics are the No. 1 cause of back and neck pain.

What are the main culprits responsible for our terrible posture?

As we age and work in sedentary jobs, there is a tendency for our heads to go forward, our shoulders to round and our bodies to slump from performing tasks in the same poor postures every day, says Marilyn Moffat, a professor at New York University and author of Age-Defying Fitness (Peachtree, 2006).

Basically, we sit too much. If we're not sitting in front of the computer, we're sitting in front of the TV, putting continuous pressure on our lower back muscles and disks.

How should you sit?

"You want to maintain the natural curves of your spine. Your head should be centered over your shoulders, not dropped forward. The upper back should not be curving forward. The front of the rib cage should be lifted slightly. Sit squarely on your bottom (walk your bottom to the back of your chair). This helps maintain natural spinal curves and gets your pelvis in a neutral position," says Novak.

What effect does posture have on back, neck and joint pain?

"When the spine is properly aligned, the muscle groups that support it are in balance and the body moves with ease and comfort," says Novak. "Poor posture causes some muscles to overwork while others just get weaker and weaker, setting up a vicious cycle."

How do you know if you have bad posture?

Moffat suggests this quick test: "Stand with your entire back against the wall. Try to place your hand, with fingers straight and in a horizontal position, in the small of your neck. How many fit? The fewer fingers that fit in that space, the better your posture is. If you can fit more than three fingers, you have poor forward head posture."

Novak recommends enlisting the help of a friend to see if your spine and joints align. From a side view:

• Your ear, shoulder, hip, knee and ankle are in a straight line.

• Your head is directly on top of your shoulders.

• Your upper back is fairly straight.

• Your shoulder blades are lying flat against your back.

• Your shoulders are straight and relaxed.

• Your pelvis is in a neutral position, belly is not hanging out.

• Your knees are unlocked.

What can we do to improve our posture?

In her book, Novak offers a "One Minute To Better Posture" technique that helps people stand straighter instantly:

• Stand with feet hip-width apart. Your knees should be soft, not locked.

• Pull in your abdominal muscles as if you're zipping up a tight pair of pants.

• Lift the front of your rib cage up as if there were a string connected from your breastbone to the ceiling, pulling you up.

• Gently, pull shoulder blades back, toward your spine, and then gently press them down, as if you wanted to tuck them into your back pockets.

• Hold the position for a few moments, trying to relax into it, breathing normally. Then relax and go through the steps again.

Charles Stuart Platkin is a nutrition and public-health advocate, and author of "Breaking the FAT Pattern" (Plume, 2006). Sign up for the free Diet Detective newsletter at www.dietdetective.com.