Good posture is in a slump. Our days at work and school are filled with non-ergonomic tasks and habits—staring at computers, lugging heavy shoulder bags, and cradling the phone in the crick of our necks. Now our backs are paying the price. According to a Duke University study, back pain is costing the country $90 billion a year.

Beyond back pain, bad posture can aggravate other problems like joint degeneration and osteoarthritis. "Bad alignment predisposes you to joint and muscle stress, which may lead to back pain and arthritis," says Shirley Sahrmann, professor of physical therapy at the Washington University School of Medicine in St. Louis.

Here's how it works—or doesn't work: Sitting at a badly arranged workspace, for example, tilts the torso forward, placing extra tension on the spine and causing it to curve. Your muscles then adjust to this newfound position. From there, chest muscles shorten and abdominal muscles weaken, while back muscles stretch and overextend. Also, this posture can compress and contribute to the breakdown of cartilage between your vertebrae. Over time, this can contribute to osteoarthritis. In short, "our bodies weren't designed to sit all day," says Tammy Bohne, a chiropractor in New York City.

To combat this rampant slouching, straightening one's back should be simple enough. But according to John Christman, standing straight is not enough. You must build, stretch, and retrain your muscles to counteract slouching. Christman, who has a Ph.D. in biophysiology, has developed an exercise program that strengthens and stretches muscles for better body alignment. "Posture is not about the vertebrae being knocked out of alignment. It's about muscle strength and you have to do the work."

Christman and Bohne offer a few tips for the slouch in all of us. First, find out if your posture is at risk by asking these questions:

1. By the end of the workday, are your neck and shoulders more tired than the rest of your body?
2. Are your shoulder muscles significantly more developed than the rest of your body? Do they feel rock hard?
3. Does a neck and shoulders massage give you tremendous relief?

If you answered yes to any of these questions, your posture may need help.

• Maintain a slight tension at your belly button, pulling it toward your back. This tightens the abdominal muscles to support your rib cage.
• Stretch your chest. Face a wall and lift one arm up at a right angle against the wall, turn your body away while your arm is still against the wall and feel the stretch across your chest. Hold for a few moments and switch sides.
• Stretch your hamstrings. Sitting shortens these muscles, causing tension in the lower back and weakened abdominal muscles.
• Strengthen your back muscles. Hold your arms in front of you, with your hands in loose fists. Pull back and squeeze the shoulder blades together.

Sometimes it's the little things that count. According to Bohne, most people are not aware of proper ergonomics.

• Be aware of your posture. The more familiar you are with proper alignment, the easier it is to maintain.
• Don't overload yourself with a heavy bag worn over one shoulder. Find a good fitting, double-strapped backpack and don't overload it.
• Avoid high-heeled shoes.
• Get a firm mattress and sleep on your side or back.
• Invest in an ergonomic chair.
• Don't cradle the phone receiver between your neck and shoulder.
• Your computer screen should be at a 15-degree angle.
• Take a break from your desk every hour or two and move around.